Nuclear Magnetic Resonance Spectrometry P. L. Corio, S. L. Smith, and 1. R. W a u o n , Department of Chemistry, University of Kentucky, Lexington, Ky. 40506
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covers the published literature from July 1969 to July 1971. A conservative estimate places the number of abstracts initially screened in excess of 7000, and it is certain that this number does not include all magnetic resonance papers related in some manner to chemical questions. The figure cited for the 2-year period leads to an average of 10 publications per day, and, since one worthwhile publication would require one or two days for its assimilation, it became evident that many articles would have to be omitted. This presented no difficulty for a large fraction of the articles, as many of them describe routine or peripheral applications of magnetic resonance. Over 3000 articles remained after obvious eliminations, an amount still too large to manage in the revidw. A second and considerably more difficult screening was required. Undoubtedly, this screening eliminated articles that should have been included, and retained articles that could have been eliminated. We beg the indulgence of those authors whose work was omitted by accident or as the result of fatigue generated by an extremely tedious task. The final number of references is well over 1000, which precluded any detailed review. Indeed, if the magnetic resonance literature continues to increase, reviews of this type will be' quite impracticable, even when the work is evenly divided among several authors. It is expected, therefore, that the most important feature of such general reviews will be citations of specialized reviews, monographs, and texts. These citations are given in the first section, which includes references to the general aspects of magnetic resonance. The second and third sections describe references relating to more specific areas of chemistry. Some overlap between these rather arbitrary divisions was unavoidable. HIS REVIEW
BOOKS AND REVIEWS
Several monographs and texts have appeared ( I A - 7 A ) which are concerned with basic reference material; two of them ( I A , 5 A ) are available in paperback editions. Specialized treatments of the analysis of high resolution N M R spectra ( 8 A ) , NMR of boron hydrides and related compounds (IOA), pulse and Fourier transform NMR ( I I A ) ,
magnetic relaxation (IdA), the nuclear Overhausa effect (ISA),and the N M R spectra of macromolecules ( I Q A ) have been issued. A compilation ( 9 A ) of 19F N M R data published from 1951 to mid-1967 has also appeared. Since the preceding review in this series (16A) other reviews have appeared discussing the N M R of organic charge-transfer complexes (16 A ) , organometallic exchange reactions (16A), water in hydrate Crystals ( 1 8 A ) , electrolyte solutions (16A), magnetic materials (16A), INDOR techniques in high-resolution N M R ( 1 7 A ) , magnetic non-equivalence related to symmetry considerations and restricted molecular motion ( I Y A ) , conformational analysis of cyclic compounds ( I Y A ) , nuclear spin-spin coupling (18A), spin-spin coupling between phosphorus nuclei (18A),nitrogen NMR ( 1 8 A ) , the narrowing of N M R spectra of solids by high-speed rotation (19A) and pulsed N M R in solids (19A). A number of chapters surveying the applications of N M R to chemistry have been included in spectroscopy texts (8OAH A ) ; these references have not been previously cited but may be of value to the reader looking for introductory material and applications to inorganic chemistry. Reviews of solvent effects in proton N M R (dQA),boron-11 N M R ( 2 9 A ) , N M R of carbohydrates and related compounds ( d Q A ) , ENDOR in liquids (dQA),proton and nitrogen N M R (dQA), conformational analysis by N M R (SOA), fluorine-19 N M R (SOA), N M R of steriods and general reviews of proton N M R (%)A, 9 1 A ) have appeared. Line shapes (SdA), anisotropic rotation of molecules in liquids by N M R quadrupolar relaxation (%A), pulsed-Fourier transform spectrometers ( S A ), spectrometers for multiple-pulse N M R ( S S A ) , N M R in helium three ( M A ) , hydrogen bonding ( S d A , S 4 A ) , paramagnetic complexes and related compounds (S5A3 8 A ) , applications of the intramolecular nuclear Overhauser effect in structural organic chemistry (SQA), long range spin-spin coupling (4OA), solvation numbers of ions ( 4 1 A ) , solvent composition and chemical phenomena (&'A, 4 S A ) , redistribution reactions ( 4 4 A ) , sulfur compounds ( 4 5 A ) and nitrogen-14 NMR ( 4 6 A ) have been reviewed. NMR studies of organolithium compounds ( 4 7 A ) and organo-
metallic compounds of the transition metals (488-61 A ) have been summarized. Double resonance techniques @ $ A ) , applications of NMR to kinetics ( 5 S A ) , petroleum substances ( 5 4 A ) and determinations of conformational barriers ( 5 5 A ) and restricted rotation in amides ( 5 6 A ) , the chemical shift ( 5 7 A ) and electronic effects induced by methyl substituents on N M R spectra ( 6 8 A ) , N M R spectra of alkenes ( 5 9 A ) , and biological applications of carbon-13 and nitrogen N M R spectra (60A) have been reported. A variety of applications of N M R spectroscopy to pharmaceutical problems ( 6 I A 4 7 A ) have been discussed. Reviews concerning the NMR spectra of carbonium ions (68A-7OA) and ion pairs (71A ) have appeared. N M R spectra of metals ( 7 8 A ) , relaxation in solids (7SA7 6 A ) , chlorine, bromine and iodine N M R ( 7 7 A ) , and aluminum-27 N M R of aluminum complexes ( 7 8 A ) have been reported. I n addition to the above reviews, a number of symposiumtype volumes (79A-86A) have appeared. A few other reviews are cited in the following sections. CHEMICAL SHIFTS
Chemical shifts studies have, as in the past, been dominated by experimental studies. One interesting theoretical observation is the possibility of field dependent shieldings ( 8 6 A ) which, though quite small for most molecules, could be observed in special cases a t very high field strengths. Approximate calculations indicate that the correction to the field-independent shielding constant for fields -60 kilogauss may range from several parts in 1O1O to 1 part in lo4. Among the more interesting experimental studies are the studies of chemical shift anisotropies in solids and liquids. The principal components of the shielding tensor in 19F powder spectrum of fluoranil were obtained by the multiple pulse dipolar narrowing method ( 8 7 A ) . The same technique applied to liquids permits an effective scaling of the chemical shift parameters in the averaged hamiltonian ( 8 8 A ) . This technique could be a useful complement to standard methods of spectral analysis. Investigations of chemical shift anisotropies as observed in the nematic phase have been reported for
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‘H and ‘OF in several halogen derivatives of methane, ethane, and benzene (894-91 A ) , Three studies have investigated the effect of an electric field on shifts of in sev‘H (98A), 2H (93A), and of eral nitriles (94A). Three other studies examined deuterium isotope effects (95A-97A), the latter reporting an abnormally large isotope effect for the bridge hydrogen in the enol tautomer of 2,4-pentanedione, Two silicon derivatives, one water soluble, have been synthesized (98A, 99A) and suggested as new reference standards for ‘H. The ‘H and IgFshifts in 1,ldifluorethylene were studied as a function of the density (100A). The temperature and pressure dependence of the ‘9F shifts of S i F d , CFI, and SFs in the gas phase were also reported (101A ) . An enormous of number of publications reported correlation studies between chemical shifts and various parameters. It is extremely difficult to make any reasonable assessment concerning the significance of these correlations. One study of solvent shifts, however, makes a factor analysis of the experiments and suggests that only 3 factors are required to reproduce the data (10ZA). Interest in the theoretical calculation of chemical shifts continues to run high, but the results, while certainly useful in supporting qualitative ideas concerning chemical shifts, are not as satisfying as might be desired. Calculations have been carried out for nitrogen compounds (103A-I06A), first row binary fluorides (107A), halo(109A-111A), methanes (108A), and ‘H in conjugated hydrocarbons (118-4, 118A) and vinyl ethers ( f l 4 A ) . The original Ramsey theory was applied to ClHz (116-4) and HartreeFock calculations were applied to ‘H shifts in HzO, NHs, CH,, and CHJ? (116A). A more general study was directed toward the theoretical calculation of first and second-order electric and magnetic properties using Gaussian-type orbitals in self-consistent MO calculations (117A).
lac
SPIN-SPIN COUPLING CONSTANTS
The status of theoretical calculations of spin-spin coupling constants is roughly comparable to that of shielding constants. A number of calculations have been carried through by a variety of methods (1l8A-1 &A), and although the results are often in reasonable agreement with experiment, it is difficult to resist the thought such agreement is frequently the result of input parameters rather than computational output. A calculation of P D in the H D molecule by the use of gaussian orbitals (14%A),which may be extended to more complex molecules, gave a value in 408R
excellent agreement with the experimental value of 42.7 & 0.5 HI. There have been hundreds of papers in the past two years reporting experimental studies of coupling constants. Investigations that have provided complete spectral analyses are mentioned in the following section. Noted here are several studies with a common theme, namely long range couplings (143A161A), signs of coupling constants (168A-l76A), and geminal and vicinal Couplings (177A-191A). SPECTRAL ANALYSIS
The application of computers in the analysis of spectra continues to be of interest (191A-800A). Iterative methods for energy levels (191A, 198A), structural data from liquid crystals (193A), magnetic equivalence factoring (196A), and the use of small digital computers have been discussed (199A). The mechanics of spectral analysis has been discussed in several papers (801A811A), including discussions of the socalled “direct method” using super operators (801A), some subtleties in ABX spectra (808A, 803A), spectra of A B X m systems (8O4A), ambiguities in the analysis of N M R spectra (106A),a paper on notation fpr various types of spin systems (.906A), magnetic equivalence in nonrigid systems (807A), and the use of double quantum transitions in spectral analysis (208A-81lA). Complete analyses have been reported for 1,2,4-trifluorobenaene (818A),cyclopropene (813A3, ethylphosphonates (814 A ) , napthalene (826A, 815 A ) , anthracene (815A), endo-bi-cyclo [2.1.0]pentan-2-01, cyclobutanol, and 1,3dibromocyclobutane (816A), a,a,a-trifluorotoluene (817A), monosubstituted benzenes (818A, 819A), oxetanes (280A, 8.91A ) , 1,1,2,%tetrafluoroethane (IbBA), butadienes (883A, 884A), thiepin 1,ldioxide (885A), pyrrole (887A), trimethylene selenide (888A), hexafluoro1,a-butadiene (829A), tricyclopropylborane (83OA), phenols (83lA), dibenzothiophene (838A), peri dialkyl napthalenes ( $ S A ) , and pentafluorothiophenol (834A). References dealing with specific types of systems include the systems AaB @MA), AiBz (836A), A3Bz (837A, 238A), ABCD (839A),ABCDE (84OA), ABMRX ( $ @ A ) , AA’X and AA’B (248A) [AXnli (243A, 244A), [AMXnlz (845A), AA’BB‘ (846A) AA’BB’X (847A), AA’BB‘BX (848A),and AA’A”A”’XX’ (249A). MULTIPLE RESONANCE AND MULTIPLE QUANTUM TRANSITIONS
Multiple resonance techniques remain among the most useful for determining the magnitudes and signs of spinspin coupling constants (850A-880A).
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Noise decoupling of H-F couplings was used in a study of trifluorochlorocyclobutanes (96OA) and the’Fourier transform method was used in conjunction with a double resonance study of acetaldehyde (868A). A double resonance method was described (8598) that detected in its natural abundance in the solid state. A method for calculating frequency shifts in double resonance experiments when the usual perturbation method fails (861A) reported that the shift is linear in [HI( rather HI2. Papers dealing with complete (ISBA) and selective (868A) decoupling of spinspin couplings have also been published. The theory of multiple quantum transitions has been discussed in several papers (880A-886A). The use of second quantization in the treatment of multiple resonance experiments and multiple quantum transitions has been described in three papers (880A, 330A338A). The halothiophenes were analyzed by means of double and triple quantum transitions (886A). CIDNP, SPIN ECHOES, FOURIER TRANSFORM METHODS
Chemically induced dynamic nuclear polarization (CIDNP) has been used to study a number of radical reactions (687A-384A). Studies have been made concerning the effect of difTusion (887A, 898A), the polariBation induced in the absence of a magnetic field (888A),and Bloch-Seigert shifts (890A). The technique has been applied to thermal (8948) and photochemical reactions (896A,897A),to reactions involving (301A-305A) , (309A, SI8A), and 1gF (3.93i-l) nuclei, and in the study of rea tions of Grignard reagents with alkyl alides (317A). The interpretation of observed polarizations is discussed in several papers (887A, 289A, 891A-.993A, S08A, 311A, S l I A , S14A316A). There have been relatively few papers dealing with chemical applications of the spin echo technique (386A-389A). Modulation of Carr-Purcell trains in homonuclear A.BX, systems have been discussed in two papers (385A, 366A), and a third (387A) discusses the CarrPurcell method in study the spin-spin relaxation of individual lines of high resolution spectra. Ionic motions in ND4PF6 were studied by the pulse method (388A),and the final paper discusses the modulation of the echo envelope arising from the transverse spinspin interactions (389A). Transform methods have been mainly concerned with the Fourier transformation (334A-S41A), but one paper also describes automatic phase correction by means of a (numerical) Hilbert transformation (333.4) . Sensitivity and signal enhancement by Fourier methods have been described (334A, %SA),
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along with several applications to biological systems (337A,338A). A pulsed Fourier transform spectrometer for studying molecules in dilute aqueous solutions has been described (336A), and two other papers discuss the theory of Fourier transform spectroscopy and available commercial instruments (348A, 343A) . RELAXATION
Among relaxation studies (344A379A), those of particular chemical interest include line broadening by molecular reorientation (344A), the measurement of longitudinal and transverse relaxation times for individual components of high-resolution spectra (348A, 349A), a study of the thermodynamics of spin systems in the rotating frame (362A), nonexponential relaxation (354A-356A), spin-lattice relaxation in periodically perturbed systems (367A) the thermodynamics of saturation (372A) and an analysis of the spintemperature hypothesis (373A). Experimental studies have described the measurement of relaxation times by adiabatic fast passages (347A), the scalar couplings in HCl and HBr (363A, 366A) , and relaxation in hydrogen gas (369A). Several papers treating line shapes and line shape analysis have also been published (361A, 376A-S79A), and random matrix analysis has been used to analyze the high resolution line shape of a cyclic tetramer of propylene oxide. An exact statistical mechanical analysis of an impurity on a linear array of spins was carried out (37OA), with results that did not agree with those predicted by the Bloch equations.
SOLIDS AND SURFACES
Magnetic resonance studies of molecular reorientations and phase transitions have been reported for a number of compounds (419A-461 A ) . A general discussion of molecular motions in organic crystals, including the narrowing of signals by sample rotation, has been presented (419A). Specific cases of molecular motions studied include HaO+ in perchloric acid monohydrate (.&OA, M I A ) , Hz0 in potassium oxalate monohydrate ( 4 M A ) and in sodium bromide dihydrate (493A), the tnt-butyl groups in hexamethylethane (4948), the methyl groups in ketones (496A), NHI in liquid and solid ammonia (496A, 49?’A), CF4 in solid carbon tetrafluoride (498A), NH,+ and NDd+ in ammonium iodide (499A) and in ammonium sulfate (43OA). Other solid states studies discuss the orientation of H20 molecules in Rochelle salt (431A) and in ferrous sulfate heptahydrate (43BA). Deuterium resonance studies have been carried out for (ND4)*BeF4 (433A), lithium hydrazinium sulfate (434A), and a single crystal of deuterated malonic acid (4364). Spin decoupling in the determination of chemical shifts in solids has been discussed (436A), along with a discussion of the absence of chemical shift anistropy in particular cases (437A). Studies of surfaces have been almost exclusively concerned with molecules adsorbed on catalytic materials. Discussions of somewhat general nature are given in several publications (469A466A). Specific studies include ion exchange resins (467A, 468A), silicaalumina (4698, 460A), silica gel (461A467A) , and zeolites (468A-477A).
CHEMICAL EXCHANGE
Nuclear magnetic resonance has been applied to the study of numerous exchange reactions, especially proton exchange (380A-389A). Other studies include hydrogen and deuterium exchange (390A-39BA) , ligand exchange in dimethyl sulfoxide complexes (393A), and in halides of methyl germanium and methyl phosphorus (394A) Restricted motions in nitrogen compounds (396A397A, @ S A ) and in halotoluene derivatives (398A) have been examined, along with a study of competitive reactions (399A) and determinations of activation energies of fast exchange reactions (4OOA). The influence of exchange has been studied in connection with relaxation (41OA, 41 1A ) and double resonance (401A, 4OBA). The analysis of exchange phenomena is usually based upon modified Bloch equations ( @ / ; A , 414A, 415A) or the density matrix (406A-409Al 418A). Applications of the moment method (4lZA, 416A) and the Anderson exchange model have also been published (427A)* I
INSTRUMENTATION
Instrumental developments of chemical interest include a synthesizer based spectrometer (478A), a pulsed spectrometer for studying molecular motions in solids (479A). The design and use of spectrometers for studies in low and high-field experiments have also been described (48OA-489A). Several methods and devices have been described for improving sensitivity in magnetic resonance (483A), in lacresonance (484A),and in pulsed NMR (486A, 486A). An inexpensive integrator for transient signals (487A),and a spin echo attachment adaptable to an HA-100 high-resolution spectrometer have also been described (4884). Other devices and techniques include a method for measuring line splittings less than 1.0 mHz (489A), methods for relaxation time measurements (490A, 491A), the elimination of rf inhomogeniety in relaxation time measurements (@,%?A), and descriptions of gas turbines for rotational narrowing in solids (493A). A modification of the pulsed gradient
method for diffusion studies has been reported (494A), and a high pressure sample cell capable of withstanding pressures up to 2 kilobars has been described (496A). A number of techniques and apparatus have been reported for use in temperature studies (496A-603A). Two of these describe the use of N M R spectra to record temperatures in the range -35.5 to +92.2 O C (4964) and in the range 175330 O K (497A). NMR IN ORGANIC CHEMISTRY
Boron. Boron-11 and proton N M R spectra have been reported for n-nonaborane( 15) (1B ) , ethoxydecaborane(l4) (BB),the product of the deprotonation of tetraborane(l0) by ammonia (SB), pentaborane(l1) (@), pentaborane(9) derivatives (6B), tetraborane(lO), pentabornane(l1) , hexaborane(l0) and hexaborane(l1) (6B). The 220 MHe proton N M R spectrum of decaborane and its derivatives have been examined (7B) in several solvents. A ring current model has been employed (8B) to correlate boron and terminal proton chemical shifts in decaborane(l4) with some success. Boron-11 and P M R spectra of polyhedral arsa- and stibacarbadododecaborane(l1) derivatives and related cage fragments (9B), monocarbahexaborane(7) (IOB),0-, m-, and p-carboranes and their B-halo derivatives (11B)and (&!-methylcarbahexaborane(7)) manganese tricarbonyl (1BB) have been reported. Boron-1 1-proton coupling has been observed (13B) in the triborohydride ion a t low temperatures. “Thermal” decoupling and apparent rapid intramolecular exchange in (C6Hs),PCuBH4 has been examined (14B) as a function of temperature. The high diamagnetism of a number of 8-alkyl and 8-alkoxyboroxins have been discussed (16B) in relation with the N M R spectra. Linewidths of 400-1000 Hz and chemical shifts were recorded (26B)for a series of cyclic boron esters of benzeneboronic acid and various dialkylaminoboronic acids. Chemical shifts of the cyclic esters were diagnostic of ring size. The spectra of a number bis(trifluoromethy1)phosof boron phinites (17 B ) , addition compounds of trialkylphosphines with bromo- and bromochloroboranes (18B), aminophosphine adducts with borine and monoethylborane (19 B ) have been described. P M R spectra indicating H-D exchange occurs between Si and B sites is reported @OB) for methyl- and silylphosphine interactions with diborane-he and -de. The spectra of liquid and gaseous boron trifluoride have been recorded (91.B) as a function of temperature and the boron relaxation times measured. The free energy of activation for intramolecular reorientation in diethyl ke-
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tone-boron trifluoride adduct has been estimated (MB) to be 8 kcal mole-'. Boron-I 1 and chlorine-35 magnetic relaxation measurements (b3B) have been employed to determine the anisotropy of rotational relaxation in liquid boron trichloride. Boron-11 NMR studies of redistribution equilibria among boron trihalides in methylcyclohexane and 1,l-dichloroethane (b4B) and of dimethyl ether adducts of boron trihalides in methylene chloride solutions (86B) have been described. The boron-ll NMR spectra of a trigonal boron cation (86B), trimethylamine adducts of boron trihalides (87B) and mixed boron trihalides (88B) have been discussed. The P M R spectra of substituted 1,3,2-diazaborcyclopentane, 1,3,2-diazaborcyclohexane and 1,3,2diazaborcyclopheptane indicate (b9B) a planar structure for the fiveand six-membered heterocycles. The spectra of dimethylpolyboranes (30B) and aminoboranes and borates (SIB) have been examined. PMR data for trialkyl-, hexaalkyl-, and trichloroborazines (%B) indicate that aromatic character is relatively insensitive to substitution whereas the proton and boron-11 N M R spectra of a variety of monosubstituted borazines have been interpreted (3SB) in terms of resonance effects on *-electron delocalization. Phosphorus. The phosphorus-31 magnetic resonance spectra of white phosphorus and solutions of white phosphorus in phosphorus(II1) bromide and organic solvents (S4B) and about 140 miscellaneous phosphorus compounds (S6B) have been reported. Spin-rotation interaction and the absolute shielding of the phosphorus nucleus in phosphoryl fluoride (96B), long-range 'JP-0-C-C-H coupling constants in 1 , 3 , 2 dioxaphosphorinanes (37B), indirect spin coupling constants in phosphorusfluorine compounds (38B), and solvent effects on the coupling constants of bis(trifluoromethy1)phosphine (S9B) have been examined. Phosphorus-31 and fluorine-19 magnetic resonance data have been described for a variety of phosphorus-fluorine compounds (4OB). The products of the reactions of phosphorus pentachloride with aliphatic nitriles (41B), phosphine oxides with phosphoryl and thiophosphoryl halides (48B), Zchloroethanol with methylphosphoryl chloride (4SB), acetyl chloride with orthophosphoric acid (44B), and hydrogen halides with dimethylaminophosphonitriles (46B) have been characterized using proton and phosphorus-31 magnetic resonance spectrometry. Studies of the trimethyl phosphite-trimethyl phosphate-phosphorus pentoxide system (46B), inorganic phosphates in strongly acidic solvents (47B), compounds containing P-0-P bonds (48B), the P-N-P skeleton (49B), alkali metal dihydrogen phos410R
phines in dimethylformamide @OB), menthyl methylphosphinate (61B), metal dithiophosphates (6bB), chlorod i m e t hylaminocyclotetraphosphazatetraenes (63B), phosphazenes (64B), spirobitriazotriphosphorine (66B),phosphorus ylids (66B), P,Pdimethyl-PI,Pl-diphenyl diphosphine disulfide (67B), and a number of phosphines (68B) have been reported. The NMR spectra of the diarsinophosphine, [(CH~)ZASIZPCF~, (69B) and organogermyl-, stannyl, and -plumbylphosphines (60B) and phosphine complexes of indium(II1) halides (61B) have been reported. A general review of the phosphorus-31 NMR spectra of coordination compounds has appeared (6bB). Articles have also appeared describing the spectra of zero-valent nickel(I1) complexes (63B), rhodium (63B, 64B), iridium (66B) palladium (64B, 66B) and platinum (64B, 67B) complexes with phosphorus ligands, particularly phosphines. Chromium (68B-78B) molybdenum (69B-72B) and tungsten (69B-7SB) phosphine carbonyl complexes have also received special attention and attempts (69B, 70B, 73B) have been made to interpret chemical shifts and various spin coupling con&ants in terms of *-bonding. Arsenic-Silicon-Germanium. Proton NMR studies of methylmonohaloarsines in equilibrium with methylamine and halogen sources (74B) cyclopolyarsines (76B), permethylpolyarsines (76B), cacodyl oxide and aresenosomethane in various organic solvents (77B) and organotin arsines (78B) have been described. Silylamines (79B), silylphosphines (80B, 81B), trimethyl-, trifluoro-, trichloro- (8bB, 83B) and triphenylsilyl derivatives (84B) of a number of functional groups have been characterized. The barriers to pyramidal inversion in some silyl phosphines have been estimated to be about 19 kcal/mole using NMR temperature dependence data (81B). The transmission of electronic effects through silicon apparently takes place via the sigma electron framework (84B). Pentafluorophenyl group IV compounds (86B, 86B), mixed group IV-group VI hydrides (87B) and silicon-germanium hydrides (88B), silylgermyl sulfide and selenide (89B), equilibria between cyclic disilthianes and trisilthianes (90B), lJ2,2-trifluoroethylidene derivatives of compounds containing Si-H and Si-halogen bonds (91B),alkylsilanes in strong acid media (98B), 1,3-dihydro-N-alkyl (aryl) disilazanes (93B), trialkoxysilanes (94B), partially fluorinated derivatives of disiloxane (96B), vinyl and allyl derivatives of group IV elements (96B), indenyltrimethyl-group IV compounds (97B) and some silicon and germanium phthalocyanines (98B) have been characterized using NMR spectroscopy.
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Proton N M R spectra have been reported for digermanyl halides and germylsilane (99B),polymethyl derivatives of digermane (1a)B) , trigermyl amine (101B),digermyl selenide and associated germanium-selenium hydride systems (IOIB), germyl isocyanate (103B), germyl-iridium carbonyl complexes (104B) and dichlorobis(j3-diketonato) complexes of germanium(1V) (106B). NMR studies of the latter compounds demonstrate the existence of both cis and trans complexes (106B). Nitrogen-14. A number of nitrogen-14 magnetic resonance studies are of particular interest. The nitrogen-14 NMR spectra of nitrogen oxides (106B, 107B), fluorides, oxyhalides (106B), nitryl halides, and nitro compounds (107B) have been recorded. Cyanates and isocyanates have also been investigated (108B) as have metal fulminates and nitrosyl compounds (109B) and cobalt(II1) complexes (110B). McGarvey and Pearlman (111B) have discussed the nitrogen-I4 N M R of paramagnetic complexes and studies of paramagnetic iron(II1)-cyanide complexes (112B) and amine adducts of nickel(I1) acetylacetonate (11SB) have been reported. Fluorine. Fluorine-I9 magnetic resonance studies of tetrakis(fluorophosphine)- and mixed fluorophosphine carbonyl complexes of nickel(0) (11423), thiophosphinyl fluoride compounds (116B), fluorophenylphosphine and arsine oxides (116B), 2-fluoro-2,2'spirobi [1,3,Zbenzo-dioxaphosphole] (117B), phosphoryl, thionyl, and sulfuryl fluorides (118B), hydrides of pentacoordinated phosphorus (119B) and the hydridopentafluorophosphate anion (12OB) have been published. Complexes of arsenic and antimony pentafluoride (121B), cis-Sba FM-and higher polyanions (188B), fluorosulfenates and fluorothiosulfinates (12SB),N fluorosulfinylamines (124B), derivatives of trimeric sulfanuric fluoride (126B), polyfluorosulfuric acid (186B), 1,2difluordisulfane 1,2-difluoride (187B), chlorofluorination products of sulfur(IV) fluorides (128B), peroxydisulfuryl difluoride (129B), the trifluorosulfur(V1) oxide cation (1SOB)and chloryl hexafluoroarsenate and chloryl fluoride (1S1B) have been characterized by fluorine-I9 NMR spectrometry. NMR studies of solutions of xenon tetrafluoride in iodine pentafluoride (132B), the xenon dioxide difluoride-xenon oxide tetrafluoride system (133B), xenon tetrafluoride (lS4B), (fluoropheny1)-stannanes, -germanes and -silanes (136B), fluorodisilanes (136B), germanium fluoride in aqueous solutions (137B),fluoroberyllates in aqueous solutions (138B), ethyl 3-(bromomercuri)perfluorobutanoate (139B), fluorine-substituted organomercury compounds (140B), aluminum (141B), gallium (142B) and
scandium (I&B) fluoride complexes in aqueous solution and metal chelates of thenoyltrifiuoroacetone ( 1 a B ) have been described. Tin(1V) fluoride compounds have received (l&B) a great deal of attention. N M R data has been provided for solutions of niobium penta,fluorosilicate fluoride in alcohols (146B) salts in solution (147B), tetrafluorooxovanadate(V) ion (148B), solutions of fluoro complexes of molybdenum and tungsten (1@B), tantalum(V) chloridefluorides (160B),fluoroalkylplatinum compounds (161B), fluorine-containing arenechromium tricarbonyl complexes (168B), and sigma-phenyl transition metal complexes (163B). The spin densities of a series of fluorinated phenoxy radicals have been determined (164B) from the shifts of N M R lines. Molecular motions near the solid-solid transition in metal hexafluorides have been investigated (166B)using fluorine-19 magnetic resonance and relaxation measurements. Solvation. Considerable effort continues to be expended on the determination of solvation numbers of ions in aqueous (166B-168B) , nonaqueous (16SB-166B) , and mixed solvent systems (166B-17OB). I n addition to reviews mentioned earlier, a discussion of selective solvation of ions in mixed solvents has been published (171B ) . A plethora of NMR data has been accumulated for solutions of diamagnetic salts in water (178B-l78B) , nonaqueous and mixed solvent systems (179B184B). The interpretation of such data frequently involves unadulterated speculation but some progress toward the elucidation of solution processes has been made via studies of molal ion shifts (186B, 186B) and reorientational correlation times (187B). The coordination of the proton of nitric acid in alkali nitrate eutectics has also been investigated (188B). Diamagnetic Complexes. The use of N M R for distinguishing geometric isomers of cobalt(II1) (189B), palladium(I1) (190B) and rhodium(II1) (191B) complexes has been discussed. The N M R spectra of acetylacetonates of titanium(1V) (198B) and magnesium (193B) have been reported, the relation of ring-proton chemical shifts to structure in chelated 2,Ppentanedionato complexes explored (194B) and electric field effects examined (196B, 196B). When electric field effects are significant, there is a linear relation (196B) between proton and carbon-13 N M R shifts and the corresponding coupling constant for both the methyl and methine groups. The stability of sodium diethyldithiocarbamate in aqueous solution (197B), sodium alkanesulfonates (198B), complexing of sodium ions in myelinated nerve (199B) , pyridine bases with iodine monochloride (8OOB), chlorine-35 chemical shifts and line
shapes of liquid inorganic Chlorides (NlB), adducts of boron trifhoride with several pentafluorides (909B), alkyl(oxinato)tin(IV) complexes (903B), tin(1V) diselenocarbamate compounds (904B), heterocyclic amine complexes of bis (N ,N 'diethy ldithiocarbamato) zinc (906B), N,N,N',N'-tetraalkylthiuram disulfides and their complexes with zinc, cadmium, and mercury (806B), silver and magnesium complexes of 1,5dimethyltetrazole and 1,4bis(lzinc methyl-5tetrazolyl) butane (907B), complexes of l,l,l-tris(dimethylaminomethy1)ethane (808B) and tin(IV), antimonyfl), and titanium(1V) complexes with psubstituted N , N d i methylbenzamides (809B) have been characterized using N M R spectrometry. A proton resonance investigation of equilibria, solute structures, and transamination in the aqueous systems pyridoxamine-pyquvatzinc (11) and -aluminum(III) has been reported (810B). This study provides additional definition of the course of nonenzymatic transamination and supports the proposed mechanism of this reaction. Conformational analysis of cobalt(111) complexes, particularly with ethylenediamine and propylenediamine ligands, has been extensively discussed (811B-8f7B) as has the use of N M R spectrometry for the assignment of absolute configurations (818B, 819 B ) . The transmission of electronic effects in ethylbis(dimethylg1yoximato)cobalt(111) (880B)and cobalt(II1) bis(acety1tone)ethylenediimine complexes (821B ) as monitored by N M R has been described. The second coordination sphere of tris(calaninato)cobalt(III) in aqueous solution has been examined (888B) using proton magnetic resonance. Complexes of cobalt(II1) with triethylenetetramine - N methyl - S alanine (883B), trimethylenediaminetetraacetate (884B), alanine (886B), ethylenediamine-NIN 'diacetate (886B), dimethylglyoxime (887B), o-phenylenebis(dimethy1arsine) (888B),ammonia (899B) and corrins (BOB) have been reported. The quasiaromaticity of thioPdiketonates and pdiketonates of cobalt(II1) have been compared (831B). Fluoride (838B), ammine (833B), alkyl sulfoxide (834B), propylenediamine (836B),N-substituted ethylenediamine (236B)and amide (837B) complexes of platinum have been characterized using N M R spectrometry. Copper-63,65 and rhenium-185,187 magnetic resonance spectra were employed to characterize cyanocuprate(1) (838B) and perrhenate (839B) solutions, respectively. Pentaammineruthenium complexes of acrylonitrile (84OB), dinitrogen complexes of osmium(I1) ( 8 4 l B ) , zirconium and hafnium acetylacetonates (84SB), EDTA complexes of lanthanides (843B) and numerous complexes containing the uranyl(1V) ion
-
(9&B, 9&B) and uranium(1V) (946B) have been characterized. The solvation of the uranyl(1V) ion in hydrochloric acid solutions in water-dimethylsulfoxide-acetone mixtures has been examined (846B). Organometallic Compounds. The large chemical shifts of hydrogen atoms bound to metals are characteristic of metal hydride complexes. Rhenium (847B) osmium (848B), and platinum (949B) hydrido complexes have been reported and the hydride chemical shifts compared with similar compounds. Proton N M R studies of dimethylberyllium adduct species in dimethylsulfide solution (860B) organosilicon acetylacetonates (861B ), alkyl (868B), and allyl aluminum (863B) species, alkoxy aluminum compounds (864B), aluminum pyridoxylidene (aminoacidato) complexes (866B), di-substituted ketimino-aluminum species (866B), methylgallium (867B) and the dimethylindium(111) ion (868B) have been reported. Silver(1) ion complexes with olefins (86923) and l13,5-trinitrobenzene (MOB) have been characterized. The proton NMR spectra of diallylmercury (861B ) , cyclopentadienylmercury (868B), indenylmercury (263B), and methylmercury (864B)complexes are reported. Proton N M R studies have been ppblished concerning a variety of organotin complexes (866B-270B), correlations with tin-1 19 Mossbauer isomer shifts found (%66B), and discussions of p r d r bonding (866B) presented. The synthesis and interpretation of the N M R spectrum of triphenyltin hydride has been described (87lB) for an undergraduate laboratory experiment. The proton N M R spectra of a number of organotitanium species (878B), chromium substituted dicarbonyls (873B), and tricarbonyls (874B), molybdenum carbonyls (876B), manganese carbonyl complexes (876B), substituted ferrocenes (877B), a-ferrocenylcarbonium ions (878B), pentadienyliron complexes (879B),olefin (880B)and *-allyl (881B) carbonyl complexes, and dimeric 2,6,7trioxa - 1,4 - diphosphabicyclo[2.2.2]octane carbonyl iron compounds (888B) have been reported. Ruthenium carbonyl carboxylates (8833) and triphenyl phosphine and phosphite complexes (884B), cobalt carbonyls containing metal-metal bonds (886B), and coordinated acetylene (886B), rhodium allene (887B) and tetraphenylborate (888B), perhaloaryl- (889B) and rindenylnickel (890B) compounds and numerous palladium (891B) and platinum (898B) complexes have been characterized using N M R spectrometry. The proton N M R studies of the spectra and ligand substitution reactions of methyl- and trimethylgold complexes have been published (893B). Chromium (894B),iron (896B) and platinum (896B) carbene complexes have also
ANALYTICAL CHEMISTRY, VOL. 44, NO. 5, APRIL 1972
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received considerable attention. By far the most illuminating application of N M R spectrometry to organometallic chemistry has been characterization of the conformational (997B) and fluxional (998B, 999B)behavior of organometallic complexes. Paramagnetic Complexes. The NMR spectra of paramagnetic species have been the subject of a number of reviews (cited above) and a book, published by Academic Press, is expected during 1972. The isotropic hyperfine shifts of paramagnetic complexes in solution arise from the interactions of unpaired electrons and nuclei. These interactions are of two types: c o n t a c t which may be interpreted in terms of the electronic structure of the species being investigated-and dipolar or pseudocontact-which may be interpreted in terms of the geometric structure of the molecules under investigation. Radical ions (SOOB) and solutions of alkali metals in ammonia (301B)have been examined but here the concern is primarily with transition metal complexes in solution. Isotropic paramagnetic shifts of NMR spectra may be employed (3OBB) to determine magnetic susceptibility in addition to providing structural information. LaMar (303B) has shown that the carbon-13 nuclear Overhauser enhancement in proton decoupled NMR spectra is reduced by paramagnetic ions as well as that the orbital ground state symmetry of metal complexes can be obtained from variable temperature NMR data (3O4B). Horrocks (303B) has discussed the evaluation of dipolar contributions to isotropic shifts while Kurland and McGarvey (306B) have examined the calculation of Fermi contact and dipolar terms. McGarvey (307B) has also considered the theory of the isotropic NMR shifts in trigonal cobalt(I1) complexes. The significance of nonzero intercepts in the temperature dependence of isotropic N M R shifts of paramagnetic complexes has been investigated (308B)and a number of possible sources of the anomalies proposed. A discussion of hyperfine coupling in fluoride and cyanide complexes has been presented (309B). Hunt (31OB) has reviewed the study of water-exchange kinetics in labile aquo and substituted aquo transition metal ions of means of oxygen-17 NMR studies. Studies of ion-pairing of iron(III), chromium(II1) (311B) and anionic lanthanide (312B) complexes have been reported. Studies of titanium(II1) chlorideacetonitrile complexes ( d l S B ) , vanadyl(IV) complexes (314B), chromium(II1) (316B),chromium(I1) (316B, 317B) and iron (111) (317 B , 31 8 B ) complexes have been described. Solvent orientation (315B) in the second coordination sphere, hindered methyl rotation in sub412 R
stituted o-phenanthroliie-chromium(I1) (316B)and low-spin d6 diimiie complexes ( 3 1 8 4 have been examined. The PMR spectra of ferrous hexafluorosilicate hexahydrate (319B)at 4.2 O K , iron(I1) amine (3SQB)and dimeric iron(111) complexes with o-phenanthroline W B ) and Schiff-base (39SB) ligands have been reported. A nitrogen-14 NMR study of acetonitrile exchange from the first coordination sphere of manganese(I1) (393B)has appeared as well as proton relaxation time measurementa (384B)of manganese(I1) ion pairs in aqueous solutions. Data for rhenium, osmium, and iridium arsine and phosphine (3,96B,396B)complexes have been presented. For some rhenium(II1) complexes, temperature studies support a second-order Van Vleck mechanism for the paramagnetism and an anisotropic susceptibility effect on the chemical shifts (SB6B). A wide variety of studies of adducts of nickel(I1) and cobalt(I1) acetylacetonates (3nB-337B) have been reported. LaMar (397B) showed that shifts for acetylacetone protons in the nickel(I1) complexes are virtually independent of the coordinating solvent. While the isotropic shifts for the nickel(11) complexes arise from a Fermi contact mechanism, the shifts of the cobalt(11) complexes represent both contact and dipolar interactions. Studies of nitrone, imine (328B), aniline (BXQB), piperidine, quinuclidine (399B), 4methylpiperidine (33OB), tropinone (331B),substituted aziridine, propylene oxide (331B),triphenylphosphine (333B, 334B) and ferrocenyldiphenylphosphine (336B) adducts have been reported. Spin delocalization in the dipyridine adducts of heteroatom-substituted bis(acetylacetonato)nickel(II) complexes has also been characterized (336B). The rate of optical inversion of the 4,7dimethyl-1,lO-phenanthroline of bis(acetylacetonato)cobalt(II) has been estimated (337B) to be less than 1 0 4 sec. Proton N M R studies of cobalt(I1) chloride-pyridine (338B) and picoline (339B) and cobalt(I1) aminopolycarboxylate (&OB) and borabenzene (341B) complexes have been reported. Oxygen-17 and chlorine-35 N M R spectra of cobalt(I1) in aqueous hydrochloric acid (342B) and oxygen-17 and nitrogen-14 NMR spectra of cobalt(I1) thiocyanate solutions (343B) have been employed to elucidate ligand substitution processes. Comparative studies of cobalt(I1) and nickel(I1) complexes of 1,3-bidentate Schiff bases (344B), bipyridine-N,N’dioxide (346B), fluoride ion (346B), diphenylsulfoxide (347B) and benzamide (348B) have been reported. NMR studies of spin delocalization of nickel(I1) complexes with Schiff bases (349B-S64B), methanol (366B),ethanol (366B),aminopolycarboxylates (367B-
ANALYTICAL CHEMISTRY, VOL. 44, NO. 5, APRIL 1972
360B), triazene l s x i d e (361B),macrocyclic nitrogen donors (369B),3-(Nsubstituted amino)methylenecamphorates (363B), phosphines (364B), 2 , s diaminobutane (366B) stilbenediamine (S66B),ethylenediamines (367B) and substituted pyridines (368B) have been reported. Heterocyclic (S69B,370B) and aliphatic amine adducts (369B) of a number of bis(0,O’dialkyldithiophosphato)nickel(II), Ni(Rdtp),, complexes have been characterized using NMR spectrometry. Primary amines and sterically unhindered heterocyclic amines form six-coordinate tram-octahedral adducts with Ni(R-dtp)2 complexes (369B)whereas secondary (370B) and sterically hindered heterocyclic amines (369B) form approximately square pyramidal five-coordinate adducts. By obtaining the NMR spectra of Ni(R-dtp)t complexes in neat amines, it is possible to observe the N-H proton contact shifts-the N-H proton resonance signals are susceptible to severe broadening and cannot be observed in dilute solutions. Proton and phosphorus-31 NMR spectra have been reported for the hexamethylphosphoramide adducts of a number of Ni(Rdtp), complexes ( 3 7 l B ) . Positive and negative spin densities were observed for protons and phosphorus, respectively. The experimental results for nickel(I1) complexes have been the subject of several theoretical interpretations ( 3 7 1 4 . INDO and modified McLachlan-type molecular orbital calculations apparently provide the best models for the interpretation of the electronic structures. Proton NMR studies of 4-methylpyridine and 4-methylpyridine N-oxide (372B) and N,N-dimethylformarnide (373B) adducts of copper(I1) ,&diketonates and bis(2-ethylhexy1)phosphoric acid complexes of copper(I1) (374B) have been reported. For copper(I1) complexes, the isotropic shifts are normally small (372B) but the NMR line broadening can be taken as a measure of complex stability (373B). The addition of a paramagnetic complex to a solution of a phosphoryl solvent results in a spin-decoupling of the phosphorus in the proton NMR spectrum (371B , 374B). Frankel (376B) has given a quantitative account of this “chernical-exchange” spindecoupling. This decoupling is dependent upon adduct formation and is also observed in many phosphine complexes (376B) of transition metals. NMR spectrometry has been used to probe the electronic structures of bisarene (377B, 378B) complexes, particularly vanadium species (377B-380B). A wide variety of paramagnetic organometallic actinide complexes have also been thoroughly characterized (381B ). The NMR spectra of paramagnetic proteins have been reviewed (382B). A
variety of studies of iron(II1) porphyrins (989B),binding of iron(II1) to conalbumin and siderophilin (984B),transferrin (S86B), manganese-activated arginine kinase (986B),nickel(I1) mesoporphyrin IX (987B), perturbation of the P M R spectrum of lysozyme by cobaltous ions (3884, manganese(I1) and copper(I1) interactions with histidine (989B)and biotin and biotin derivatives (%OB) have been reported. The interaction of cobalt(I1) with imidazole ( N I B , JSdB) and nucleosides (99dB) has been characterized. Although the amount of literature concerned with the N M R spectra of paramagnetic complexes is increasing year by year, much fundamental work remains to be undertaken. The characterization of the chemical shifts and relaxation times of all the nuclei in selected complexes, e.g. Mn(O=P [N(CHa)2]3)r2+ (manganese-55, oxygen-17, phosphorus-31, nitrogen-14 or -15, carbon-13, and hydrogen-1), are particularly desirable in order that reliable models for electron epindelocalization in paramagnetic complexes may be constructed. The availability of molecules for which the structures and spin densities of the various Ptoms are known is fundamental to I he understanding of the various interactions present in paramagnetic complexes. N M R Shift Reagents. The overlap of proton reson.mces in complex molecules renders the evaluation of chemical shifts and coupling constants difficult. Solvent shifts, INDOR or spin-decoupling experiments, formation of derivatives, cleuterium substitution, and use of higher frequencies can all be employed with varying success to resolve complex spectra. Since 1969, when Hinckley (89SB) demonstrated that large isotropic shifts are produced for the proton resonances of cholesterol when it is placed in solutions of the dipyridinate of tris(dipivaloy1methanato)europium (111), Eu (dpm) 3 (py) 2, .a great deal of interest have been shown in lanthanide "shift reagents" for the simplification of the N M R spectra of complex molecules. One of the most striking examples of the use of lanthanide shift reagents is the first-mder proton N M R spectrum of n-hexanol published by Sanders and Williams (S94B). The ability of paramagnetic rare earth complexes to induce large changes in chemical shifts with relatively small line broadening effects has led to a large (SQSB-476B) number of applications of these reagents in a short time. The cited references are by no means all of the papers which have appeared following Hinckley's original finding (S9SB), Considering the present space limitations, not all of the applications could be discussed even in a perfunctory manner. Fortunately, several reviews of the applications of lanthanide shift reagents
are scheduled to appear during 1972. Already one review, in a chemical s u p ply house bulletin (476B),has appeared. Available evidence suggests that the origin of the large isotropic shifts produced with lanthanide shift reagents is associated with adduct formation by the lanthanide chelate with the molecule of interest. The interaction of species in solution to yield NMR spectra resolution is not really new since it has been known for years that hydrogen bonding (477B) can produce such a result. However, with lanthanide shift reagents, large upfield or downfield shifts in resonance positions are produced upon complex formation. A recent survey of lanthanide shift reagents (478B) (which also serves as a useful starting place to find the literature) gives rather convincing evidence that the observed shifts are dipolar in origin. Although the bulk of shift reagent work involves paramagnetic lanthanide chelates, a few papers have also concerned themselves with the use of cobalt(11) and nickel(I1) (41OB, 479B-481 B ) chelates. Generally, the paramagnetic broadening produced by these complexes imposes rather severe restrictions on their use. In addition to spectral clarification, the lanthanide shift reagents have a variety of analytical applications, e.g., the analysis of mixtures of alcohols (488B). It is expected that the analytical applications will undergo considerable development in the near future. For those readers undertaking the preparation of shift reagents, the papers by Selbin, Ahmad, and Bhacca (48SB) and Lyle and Witts (484B) should be consulted. Other Nuclei. Halogen N M R ( I C ) and the aluminum-27 N M R of organoaluminum compounds ( 8 0 have been reviewed. Deuteron magnetic resonance of deuterohydrocarbons (SC), acetates and lactic acid (4C), derivatives of tram4tert-butylcyclohexanol (6C)and several paramagnetic transition metal acetylacetonates (6C) have been reported in addition to the deuteron N M R of deuterium oxide in the presence of salts and in hydrated collagen fibers (7C). Lithium-7 magnetic resonance has been reported for ethylenelithium acrylate polymers ( 8 0 alkyl- ( 9 0 and aryl-lithium ( 1 0 0 , lithium carbonate, oxide, and chromite (IOC) and the mineral eucryptite (1%'). The proton and beryllium-9 N M R spectra of a number of alkylberyllium compounds ( I S C ) in solution have been described. Papers have appeared describing oxygen-17 NMR of acetophenones ( 1 4 3 , aliphatic nitro compounds and their anions (16C), various phases of water ( 1 6 0 and water-ammonia solutions (17 0 and aqueous solutions contain-
ing hydrated vanadium(I1) and chromium(II1) (ISC). The spin-spin coupling constants J("Mn-I7O) (= 190 f 25 radians/sec) in MnOl- and J(18C-170) (= 140 25 radians/sec) a t 25' were determined ( 1 9 0 by comparing their experimental N M R spectra with computer simulated spectra. Sulfur-33 magnetic resonance for thiophene ($OC), selenium-77 resonance in organoselenium compounds (81C), and tellurium chemical shifts for solid (22C) and liquid (230 tellurium have been reported. Sodium-23 magnetic resonance has been discussed for aqueous solutions of halide salts (24c), aminocarboxylate complexes (86C), and single crystals of sodium nitrite (26C)and sodium periodate ( 8 7 0 . Measurements of cesium resonance have been made for the liquid cesium-oxygen system (88c) and cesium ions in solutions (89C). Calcium-43 relaxation times have been measured (SOC) for aqueous adenosinetriphosphate solutions. These results indicate that calcium-43 magnetic resonance will be useful for the study of biologically significant compounds. Aluminum-27 magnetic resonance has been reportvd for a variety of octahedral and tetrahedral complexes in solution ( S I C ) and for ruby and spinel lattices (SBC). Chlorine-35 magnetic resonance studies of the ionization of perchloric acid in aqueous solution (SSC), fluorohalodinitromethanes (SIC), organophosphorus compounds containing a P-C1 bond (S6C), cobalt(I1) carbonic anhydrases ( 3 6 0 , liquid chlorine and aqueous chlorine solutions (S7C), zinc carbonic anhydrase (S8C), zinc nucleotide diphosphote complexes (SQC),lithium chloride solutions in methanol-water mixtures (doc), aqueous solutions of alkali halides ( 4 I C ) , concentrated lithium chloride solutions (48C), Escherichia coli alkaline phosphatase (bSC), and CsCoCls and CsMnCla (44C) have been reported. The nuclear quadrupole relaxation of bromine-79 in aqueous solutions of mono-, di-, and trialkylammonium bromides in aqueous solution has been studied (46C). The ratio of the nuclear gI factors of bromine-79 and bromine-81 have been accurately determined (46C) using NMR. Xenon-129 magnetic resonance has been reported for mixtures of xenon and other gases (47C), xenon near the critical point (48C) and xenon difluoride and tetrafluoride solutions in liquid NOF 3HF (49C). A chromium-53 magnetic resonance study of the chromate-dichromate equilibrium (603,manganese-55 studies of manganese oxide (61C), manganese decacarbonyl (68C), rubidium trifluoromanganate (630,permanganate solutions ( 6 4 0 and manganese(II1) in a single crystal of manganese ferrite (66C),cobalt-59 studies of cobalt(II1) complexes (66C) and cadmium-1 11 and -113 resonances in chromium chalco-
*
e
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genide spinels (6712) have been described. Magnetic double resonance studies of tin-119 chemical shifts in organotin compounds (680, antimony-123 resonance in NaSbFs (690, niobium-93 N M R in lithium niobate crystals ( 6 0 0 , rhodium-103 resonance in complexes (610 and europium-151 and -153 resonance in solids (680have also been reported. Analytical Applications. General reviews (1D,9D) of the analytical applications of NMR spectrometry have appeared in addition to reviews concerned with the determination of water , pesticides (4D), barbituin coal (SO) rates (60)and various pharmaceutical products (6D,7D). A small general purpose computer for use with a high resolution N M R spectrometer for quantitative analytical chemistry (8D)and the effect of o p erating conditions on the accuracy of spectral measurements (9D)have been discussed. Applications to the determination of isotope distribution (fOD), ~ K B H for + aliphatic ketones ( l l D ) , organosilicon compounds containing SiF bonds (IdD),barbiturates (ISD), hallucinogenic drugs (140) , DDT-type pesticides (16D),carbamate pesticides (16D), 2,4-dichlorophenol in dichlorophenol isomers (17D), toxic solvents in paints, varnish removers, and sewage solvents (18D), detergents (19D), gasand water in benzeneolines ($?OD), sulfonic acid (91D)have been described. The use of hexafluoroacetone as an N M R reagent (bBD),J(P-C-H) coupling constants for the identification of cyclic phosphines ( d S D ) , application of N M R to semicontinuous reaction monitoring (B4D), submicrodetermination of functional groups by time-averaged N M R (86D),and automatic moisture measurements of lignites (96D)have been reported. The N M R spectra of the enantiomers of a given a-amino acid methyl ester differ appreciably in optically active 2,2,2trifluorophenylethanol solvent. This spectral nonequivalence is widely applicable (27D) to the absolute determination of the optical purities of a number of amino acids and the correlation of the absolute configurations of nonsubstituted glycines. Many products obtained by electrophilic aromatic substitution reactions in 3,3'-bithienyls are easily converted to carboxylic methyl esters whose structure can be determined by proton NMR spectrometry (280). This method might also be valid for other biaryl systems. Time-averaged NMR spectrometry has been applied (890) to the quantitative determination of dicyclopentadiene, 1,4-hexadiene, and ethylidene-norbornene in samples of ethylene - propylene - diene rubbers. The development and application of 414R
rare earth shift reagents is discussed elsewhere in this review. Liquid Crystals. The use of liquid crystals in N M R spectrometry has been the subject of a number of reviews (IE4E). Difficulties in the interpretation of the NMR spectra of oriented molecules have been discussed (6E,6E). B. P. Dailey and his group have shown ( 7 4 that the analysis of the spectra of suitable nematic liquid crystal solutions offers a convenient method for the determination of nuclear quadrupole coupling constants for molecules in the liquid state. Details of the rholecular structures of cyclobutane in the nematic phase of p,p'-bis(n-hexy1oxy)azoxybenzene (8.9 add allene in the same solvent (9E)have been reported. The results agree favorably with electron diffraction data. A number of relaxation time measurements (IOE) in liquid crystals have been reported. The NMR spectra of tetrafluoro-l,3dithietane in a lyotropic mesophaae ( I I E ) , sodium fluoride in a synthetic smectite (IbE), mesophases of vinyl oleate (1SE)and ethanol in lyotropic mesophases (14E) have been described. B. P. Dailey and his group have extensively examined (16E-19E)the chemical shift anisotropy of a variety of molecules in liquid crystal solvents. Calculations and experimental data are detailed in the cited papers. The spectra of truns-l,2dicyanoethylene (bOE), benzofurazan oxide ( g I E ) , partially deuterated acetonitrile (WE)phenylacetylene (2SE) ethyl fluoride (24E), &-1,2dichloroethylene, furan, thiophene, and benzene ( M E ) , fluorobenzene compounds (ME),anisylidene p-aminophenylacetate (b7E), (28E), deuteriomethane phosphine (,%?E), trichloro- and tribromobenzene (SOE), spiropentane (SfE ) , ethylene (SBE), dimethylmercury ( S S E ) , o-terphenyl (84E), 1,l-difiuoroethylene (S6E),cis-l,2difiuoroethylene and vinyl fluoride (S6E), 1,4naphthoquinone (S7E), lJ-dichloroethanes (S8E), 2,6dichlorotoluene (S9E), o-chlorotoluene (4OE), bullvalene (41E ) , methyl and methylene halides (4dE) and r-cyclopentadienyl-tungsten hydride (@E) in various nematic phases have been described. Poly (7-benz yl-cglutamate) solutions have been examined using nitrogen-14, chlorine-35 and spin-echo techniques (44E-46E). The nitrogen14 NMR spectrum in the nematic phase and linewidth in the isotropic phase of p-azoxyanisole have been reported (47E). The linewidth, A, in the isotropic phase follows the relation Aa(TT * )l I 2 where T* is a temperature slightly below the nematic-isotropic transition. This is interpreted in terms of the local order fluctuations expected in the vicinity of a weakly lsborder transition. Polymers. Reviews of the applications of NMR spectrometry to the study
ANALYTICAL CHEMISTRY, VOL. 44, NO. 5, APRIL 1972
of polymers (IF), biopolymers (BF), polymer configuration and conformation (3F) and molecular relaxation mechanisms in *polymers (4F) have ap peared. The direct spectra of "C in natural abundance have been reported for (6F) poly(viny1 methyl ether), polystyrene (isotactic and atactic), poly(methy1 methacrylate), polypropylene (isotatic and atactic) and (6F) 1,4-polybutadienes and l,.l-polyisoprenes. The diacrimination of configurational sequences (6F) is at least equal to that possible in proton spectra a t 220 MHz. Motional narrowing was observed (6F) to 'be adequate to obtain high-resolution spectra, with proton decoupling, of bulk samples of cM-l,4polybutadiene and cis- and trans-l,4-polyisoprene. A variety of studies a t 220 MHz have been reported for polypropylenes (7F9F),ethylene-vinyl formate copolymers (IOF), poly(methy1 methacrylate) (11F),poly(viny1 chloride) (IIF),propylenes-ethylene copolymers (ISF),and poly(a-methylstyrene) (14F). Proton spectra of a number of polymers a t 60, 100, and 220 MHz were compared ( I 6F) and spectra obtained with a 220 MHz superconducting solenoid spectrometer approached first order, permitting more detailed information to be obtained and, in most cases, eliminating the necessity of spin-decoupling experiments in stereoconfiguration determinations. Techniques for the determination of polymer composition of rubber vulcanizates (16F) and for the rapid and efficient removal of viscous polymer solutions from NMR sample tubes (17F) have been described. Proton NMR studies of poly-cprolines (18F),copolypeptides of cproline with 7-benzyl cglutamate (19F),temperature denaturation of single-chain polyadenylic acid @OF), anionic graft polymerization of propylene oxide on starch (81F) and poly-c and POlY-DG alanine in helix-random coil-interconverting media (2bF) have been reported. Micelle formation in the sodium caprylate-caprylic acid-water system (2SP), heptafluorobutyric acid (24F) and polyoxyethylenated dioctylphenol and hexaoxyethylene glycol-water solutions (B6F) have been examined. Pulsed NMR studies ( M F ) of poly(tetrafluoroethylene) (Teflon) have demonstrated that a phase transition occurs a t +6 OC. A study of solid poly(oxymethylene) (d7F) between - 170 and 100 OC indicated that even in an ideally crystalline state, polymer mole cules are engaged in a complicated oscillation of large magnitude. The temperature dependence of the proton relaxation time of solid isotactic polypropylene (,98F)was measured a t 4, 30,44, and 86 MHz and over the range 100-430 OK. The relaxation was quantitatively discussed in terms of two jump models with
distributions of correlation times for chain and methyl group motion within the amorphous and crystalline regions. Magnetic relaxation has also been studied in polyisoprene (99F),polyethylenesalt solutions @OF) , polyethylene @IF), polystyrene and poly(vinylpyrro1idinone) solutions (39F), benzene in solutions of syndiotactic poly(methy1 methacrylate) (MF),bisphenol A polycarbonate, butyl rubber, and their composites (34F), poly(ethy1ene terephthalate) (36F) and polymers containing pphenylene units (36F). The Bell Telephone Laboratory group (37F) has published relaxation data for a wide variety of polymers. The high resolution N M R spectra of vinyl chloride-etbylene copolymers obtained by trialkylboron catalyst showed (38F) that copolymer composition could be determined from the resonance peak area. The monomer reactivity ratios thus obtained were in good agreement with those determined from elemental analysis results. N M R analysis of chlorinated poly(viny1 chloride) (39F) showed that chlorination does not take place in the crystalline regions of the polymer and that chlorination can be influenced by the steric configuration of the chain. Stereochemical equilibrium and configurational statistics in oligomers of poly(viny1 chloride) (4OF) and polystyrene (41F) have been reported. The chemical shift contribution of the magnetic anistropy effects due to side chain carbonyl groups has been calculated (49F) for methylene and a-methyl protons of isotactic poly(methy1 methacrylate) using 51 and d helical chain models. The 51 models explain the observed values better than the & model. High resolution P M R data for poly(vinyl formal) and its model compounds (43F), poly(N-vinylacetamide) and dimeric model compounds (&F), poly(vinyl chloride)-&@dz (46F) poly(propene-24, sulfide) (46F) and isobutylene-chlorotrihoroethylene copolymers (47F) have been reported. Approximate relations between the chepical nonhomogeneity (expressed by mean square deviation of the local composition from the average value) and the concentrations of monomer sequences, such as diads, triads, etc., have been derived (48F). The conformational analysis of polymers, stereochemistry, and sequence distribution of copolymers have been the subject of a number of papers (49F-64F). Polymerization of coordinated monomers, e.g., methyl methacrylate complexes with boron trifluoride, tin(1V) chloride and aluminum chloride (66F)and acrylonitrile, methacrylonitrile, and methyl methyacrylate with zinc chloride (66F, 67F) with styrene, has been examined and NMR has been employed in conjunction with ESR and ultraviolet spectrometry to elucidate and characterize the various species
formed. These latter studies emphasize the necessity for examining systems of interest using more than one spectrometric technique. ORGANIC, BIOLOGICAL, SOLVENT PHENOMENA
Detailed second order analyses of complex organic compounds have a p peared with increasing frequency. Examples of three-membered ring systems include cyclopropanes (1G) and epihalohydrins (8G, 3G). Cyclobutanes (4G), cyclopentadiene trimers (6@, and homoadamantane (6G) are representative of studies involving middle sized and bridged ring systems. The pyrrole spectrum has been analyzed extensively including *4N (7G) and 15N (8G) spectra or decoupling experiments. Large numbers of mono- (9G)di- (IOG) and trisubstituted benzenes ( I I G ) have been analyzed as have various heterocycles such as pyridone-2 (I9G), benzodioxin and benzodithin (ISG), azaindoles (14G), and various substituted pyridines and their conjugate acids (16G). Monosubstituted naphthalenes (16G) condensed benzonoid hydrocarbons (17G) and dibenzacridine (18G) are examples of well analyzed polycyclic aromatic compounds. The complete analysis of the octafluorostyrene spectrum (19G) and of tri(2pyridyl)phosphine (9OG) are representative of the increasingly common appearance of detailed analyses of nonproton spectra or of multinuclear studies. Much effort has been expended in elucidating the effect of various substituent groups on the chemical shift and coupling constants of adjacent protons. For aliphatic compounds such studies include substituent electronegativity and magnetic anisotropy effects on proton shifts in tert-butyl groups (91G), methylene ring protons in steroids (MG), various substituted ethylenes ( H G , 94G) and simple esters (96G). Both substituent effects on cyclopropyl protons (96G) and the cyclopropyl group as a substituent (97G) have been examined. Intramolecular van der Waals (dispersion) interactions have been invoked to explain the effect of Nsubstitutents in aziridines (9886). Studies of 5,6-dicarboxy-2-norbornene derivatives (99G) are representative of investigations of substituent effects and stereochemistry. I n a reversal of the usual substituent effect studies the additivity of alkyl group effects on ‘9F spectra in adamantanes is reported (3OG). Among the aliphatic heterocycles, the substituent effect in 1,3-dioxanes has been studied extensively (31G-153G) as have the analogous sulfur (33G) and nitrogen (34G) compounds. Unusual among the many reports of studies of particular functional groups are reports of the substituent effect of
various phosphorous containing functional groups on aliphatic protons (36M7G). By far the largest number of substituent effect studies have used benzenoid systems. Certainly the most startling reports of substituent group effects involve the deuterium isotope effect on ‘OF shifts in fluorobenzenes (98G, 99G). I n cases involving hyperconjugation @-shiftsas large as 22 ppm have been observed (SQG)! Among other uncommon substituent groups which have been examined are 1x2and 1x4 effects on ‘OF shifts (4OG) and the polysulfide group effect on protons (41G). Along more conventional lines, the thiourea group in aryl methyl thioureas has been assigned a Schoolery constant of 2.6 ppm for the methyl group shift and an ortho and meta substituent effect of -0.03 ppm (4BG). Anomalous chemical shifts in nitrosobenzenes are attributed to the nitroso group magnetic anisotropy (49G). The substituent effect of a variety of silicon and germanium containing functional groups has also been elucidated (44G-46G). The effect of phosphorous containing functional groups on proton shifts in furan, thiophene, and pyrrole has been reported (47G). Of particular utility are additive substituent relationships which permit assignment of functional group positions in polysubstituted benzenes (48G). Considerable attention has focused on the mechanism whereby substituents affect chemical shifts. Inductive, resonance, electric field, and steric mechanisms have been reported for substituent effects on benzene ring proton shifts (49G-67G). Analogous studies report similar results for 19F shifts in benzenoid systems (68G46G). Particularly interesting are examples of metalloid substituent effects involving d,-p, bonding (666, 66G). The transmission of substituent effects through aromatic rings or other functional groups has received considerable attention. I n the simplest cases, substituent effects on methyl groups in substituted methyl benzenes (670) or aliphatic C-H shifts in benzylic protons (68G-7OG) have been reported. Studies of 14N shifts in substituted anilines (71G) and shifts in substituted phenylphosphonic acids ( V G ) are characteristic of the increasing use of “other nuclei” in organic magnetic resonance. Longer range effects involving transmission of substituent effects through a benzene ring and amides (73G), a m groups (74G), sulfide, sulfoxides, and sulfones (76G-77G), cyclopropanes (78G), and oxirane rings (79G) have been reported. Particularily interesting is a two-way study of transmission effects of substituents across the azomethine group in benzylidine anilines showing different effects depending on whether the substituent is located on
ANALYTICAL CHEMISTRY, VOL. 44, NO. 5, A P R I L 1972
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the aniline ring or the benzylidine ring (800 * Efforts to correlate chemical shifts and coupling constants with empirically or semiempirically calculated parameters, usually LCAO-MO approaches, have met with varying success. Recent efforts include studies of cyclic and acyclic olefins, dienes and trienes (81G, 82G), and a variety of benzenoid compounds ( 8 3 G 8 7 G ) as well as nonalternate aromatic hydrocarbons and ions (87G). Among heterocyclic systems substituted thiophenes and furans have been studied using both simple Huckel and CNDO approaches (886, 89G). Pyridines, quinolines and quinoxalines (90G, 91G), pyrimidines (990,phenanthrolines (93G), various tricyclic heteroaromatics ( 9 4 0 , cyanines and oxonols (96G) and pyrylium salts (96G) also show various correlations between calculated parameters and their chemical shifts or coupling constants. Bond fixation in cyclic unsaturated systems has been studied in methyl arenes (97G), fluoranthrene (98G) and a variety of heterocycles (99G-108G). The llB spectra criteria for aromaticity of 10,Q-borazaronaphthalene represents another application of “other nuclei” in the organic field (108G). Ring current effects have been evaluated in methyl arenes (103G) and a variety of condensed benzenoid hydrocarbons, particularily in attempts to evaluate the McWeeny theory (lOdG, 106G). Calculations of ring current effects in fluoranthene (loSG) suggest that fivemembered rings exhibit only ca. 5% of the effect attributable to benzene rings. Prophyrins ( 1 0 7 0 , fluorene, dibenzofuran, and carbazole (108G) and 1methylphosphole (1090 have all been examined for ring current effects. Annulenes have received their usual share of attention (llOG, 1 1 1 0 . Of particular interest is the reported observation of a paramagnetic ring current in the dianion of trans-15,lgdialkyldihydropyrenes. Contrary to the usual observations, the interior protons shift downfield by 25 ppm while the exterior protons shift upfield by 12 ppm. Direct observation of carbonium ions constitutes one of the most significant applications of NMR techniques in recent years. Recent investigations report the observation of tert-amyl cation (113G) from alkyl halides and AIBra. Protonation of various oxygen and sulfur (thio- and thiono-) systems ( l l 4 G 116G) yielded spectra of aliphatic cations. Investigations of trithienylmethyl carbonium ions ( l l 7 G ) and alkyl: and aryl- halocarbonium ions (118G) have appeared. Classical systems retain their interest as demonstrated by spectral studies of allyl (1190 cyclopropenyl (120G, 121G) and cyclopropyl-carbinyl cations (122G). Cyclobutyl (123G) and cyclobutenyl
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ANALYTICAL CHEMISTRY, VOL.
(184Gl cations have been studied. The norbornyl cation continues to receive extensive study (1~6Gl30Oc). Carbonium ion spectra have been used to elucidate hydride transfer mechanisms (131G, 138G) and a variety of rearrangement reactions (133G136G). Such studies are so common that we now find studies of chirality of cations (186G). Carbanions have begun to receive almost as much attention as carbonium ions. A variety of studies, frequently a t low temperature, of various saturated, unsaturated, and aromatic carbanions have appeared ( 1 3 7 G 1 4 6 G ) . A few investigations have focused on the effect of the cation OR the NMR spectrum of carbanions (1‘46Gl49G). Use of I4N, and l6N spectroscopy to study nitro carbanions is a further illustration of “other nuclei’’ applications in organic chemistry ( 1 6 0 G 1 6 8 G ) . Proton NMR has been used to investigate a variety of other ions containing positive oxygen (163G, 164G), sulfur (166G), nitrogen (166G, 167G) and phosphorus (168G). The effects of protonation of nitrogenous heterocyclic aromatics and aromatic amines have been reported (169G-164G), as have studies of protonation of amides ( 166G168G), thion- and dithio esters (169G), thienyl carbonyl compounds (17 0 G ) , and phosphones (171G). As noted earlier, it is impossible to list all the literature examined. A representative sampling of general organic applications of high resolution magnetic resonance spectroscopy might include studies of polycondensed aromatic compounds (17BG-176G) ; a variety of nitrogenous heterocyclic aromatics (177G-19OG) including applications of 15N spectroscopy (191G193G); natural products such as alkaloids ( l 9 4 G ) , coumarins (196G, 196G) and steroids (197G, 198G); other heteroatom systems containing Se (199G-206G), Ge (200G-206G), Sn (206G) and As (206G); and organometallics containing Cu or T1 (207G, 808G) and various metal cyclopentadienides (209G-211G). Although coupling constants have been covered above, we should mention the wide spread observation and application of long-range coupling constants as typified by reports involving bicyclobutanes (218G), various saturated and unsaturated aliphatic compounds (213G-d16G), polycyclic phosphorous containing materials (217G, 218G) and aromatic compounds (219G-226G). Particularly interesting are long-range couplings involving *lP (217 G ) and ‘9F(824G-226G). Additional examples of organic applications include studies of Cope rearrangements in semibullvalenes (227G) and bond shifts in cyclooctatetrane ($286). Conformational and stereochemical
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problems continue to constitute significant applications of high resolution magnetic resonance spectrometry. New techniques include correlations between the ratio of vicinal proton couplings and dihedral angles for six-membered rings (229@, conversion of 1,2-diols to dioxalanes which permits determination of stereochemistry without having both possible isomers present (23OG) and the use of SO2 complexes with nitrogen to study inversion phenomena ($31G ). Evidence for the inapplicability of the chemical shift method for conformational analysis of quaternary salts of piperidines has appeared (232G). Further examples of structural and conformational assignments from acetylation shifts (833G, 234G) are greatly enhanced by utilization of the much larger ‘9F chemical shifts from trifluoroacetyl derivatives (836G-243G). Investigations of rotational barriers and conformational preferences continue to represent major applications of NMR techniques. Rotation about single bonds between spa hybridized carbons in substituted ethanes (244G249G), propanes (860G) and butanes (261G-263G) have been studied as have rotations about C-C single bonds between sp* hybridized carbons in vinylcyclopropanes (264G, 266G), vinylethylene oxide (266G),butadiene (267G) and diimines (268G). Rotations about C-C single bonds of halomethyl groups on benzene rings (259G-262G) and various other substituent groups on aromatic rings (263G-868G) have been studied. Rotational barriers for C-C double bonds have also been investigated (269G, 27OG). Rotational barriers in amides (271G-282G), thionamides (283G-286G) and benzamides (286G-288G) have been studied exhaustively. Conformational studies of substituted acetaldehydes (289G-Z9iG), cyclopropyl ketones (292G), and acetyl and formyl substituted furans, thiophines and pyrroles (893G-297G) represent further examples of studies focused on C-C single bond rotations, Utilization of NMR techniques to study rotational phenomena is limited only by the imagination of the investigator as evidenced by studies of rotation about single bonds between C-0 (298G-300G), C-N (301G-306G), P-N (306G, 307G), B-N (308G, 309G), S-N (JlOG, 311G) and N-N (312G314G). Ionic species have received their share of attention concerning both rotation (316G) and ring conformation (316G-Sl8G). Conformational studies of small rings include cyclobutanes (919G), and a variety of five-membered rings including furans (380G, 321G), cyclic carbonates (328G), dioxolanes (323G) and their sulfur and germanium analogs (324G, 326G), phospholanes (386G, 327G), and numerous sugars and sugar derivatives (328G-332G).
The conformational preference of various groups in six-membered rings (333G-337G) received attention. Conformational studies of cyclohexanes (338G-346G) , cyclohexenes (346G, 347G),and cyclohexanones (5.4886-361 G), or their derivatives (36SG) continue. Six-membered carbocyclic rings in dihydronaphthalenes (363G),decalins (364G, 366G), 9,lO-dihydroanthracenes (366G369G) and 9,lO-dihydrophenanthrene (360G) also were examined. Conformational investigations of heterocyclic sixmembered rings included piperidines (36lG-366G) and other nitrogen heterocycles (367G, 368G), pyrans (3696372G), vast numbers of l,&dioxanes (373G-386G) , cyclic sulfites (387G3896), phosphorinanes (390G-393G) , and miscellaneous other compounds (394G-396G). Seven-membered (39740lG), eight-membered (408G, 40SG) and larger rings (404G, 406G) have also been studied. Examples of conformational studies of more complex ring systems include a variety of bridgehead nitrogen systems (4O6G-41 I G ) , various bicyclo systems (413G-417G) and several cyclophanes (418G-4SSG). Nitrogen inversion in substituted hydrazines (424G-427G), imines (498G), amines (429G-43lG) and several ring systems (432G-438G) continues to be of interest. Phosphorous inversion in phosphines (439G, 440G) has also been studied. The intimate relationship between stereochemical problems and concepts, and N M R spectrometry continues to develop. Utilization of N M R to determine enantiomeric composition of alcohols and amines by derivatizing such compounds with a-methoxy-a-trifluoromethylphenylacetic acid is reported as being generally applicable (441G). Studies of achiral acid-achiral amine systems (44SG) and use of achiral solvents (443G) expand the application of NMR to the determination of enantiomer distributions. Symmetry or asymmetry and its affect on N M R parameters is emphasized by reports of intrensic diastere otopism in a variety of systems (444G447G). Examples of magnetic nonequivalence abound as typified by the reported chemical shift difference of 4.08 ppm for the methylene protons in a complex dinapthothiocin (448G), Various examples of “double magnetic nonequivalence” have also appeared (449G461 G). Nonequivalence attributable to asymmetry at phosphorus (46SG, 463G) and pseudorotation in phosphoranes (464G-466G) represent further examples of the NMR-stereochemistry relationship. A pleasing resurgence of biochemical and biological applications of nuclear magnetic resonance techniques is apparent. Some problems have appeared,
notably the report t h a t the common water soluble reference compound 2,2dimethyl 2 - silapentane - 5 - sulfonate (DSS) acts as an activator of carboxypeptidase A (4670). However, generally beneficial results such as the use of the I9F shift in trifluoroacetic acid solutions of polypeptides as a probe of helix-random coil transformations (4686) promise greater utilization in the future. Particularily significant is the widespread nature of biochemical applications of NMR. A sampling of general applications includes conformational studies of acetylcholine analogs (469G), investigations of tocopherols (460G-&ZG), and utilization of IH spectra of fully deuterated or partially deuterated proteins (463G-466G). Vitamins have received fair attention. Pyridoxal systems (466G-468G) ,vitamin Blz (469G), and ascorbic acid (470G) have been studied for several viewpoints. Other diverse materials examined include mycobactins (47lG), cytochrome c (478G), xanthones (473G), heme A (of cytochrome c) (474G), porphyrins and chlorins (476G), numerous fatty acids (476G-480G) , phospholipids (481G ) and lipoproteins
-
(48W*
I n the carbohydrate area large numbers of monosaccharides (483G-.496G), mostly methyl or acetyl derivatives (483G-490G) have been examined to determine conformations. I n a few interesting cases 16N spectroscopy has -been used to study amino sugars (496G, 497G). Disaccharides (4986, 4996) and polysaccharides (600G-606G) have also been studied. Simple amino acids have been studied to determine conformations under different conditions (607G),in the presence of metal ions (608G, 609G), or as salt solutions in various solvents (610G). Conformational studies of dipeptides (611 G616G) and polypeptides (616G-621 G) are prevalent. I n one case, 220 MHz spectra of a polypeptide allowed assignment of over 215 specific resonances implying the possibility of sequence determinations or specific interaction site determinations (6SSG). Utilization of a variety of N M R techniques has led to the complete assignment of the actinomycin D spectrum (623G). Exchange reactions (6S4G1 686G) and complex formation with metal ions (6S6G) or phospholipids (6876) have also been studied. I n all cases these studies on small systems provide model data for investigations of large naturally occurring proteins. N M R is now commonly used to investigate primary and secondary structure in many naturally occurring peptides and proteins (628G-646G). Binding of various substrates, inhibitors, and activators to proteins is frequently examined (646G-660G) as is the interaction between proteins and metal ions (661G-668G). Utilization of thal-
lium-205 resonance represents an unusual example of such studies (6696). Various metal containing globins have also received attention (67OG-6766). Of particular value for N M R investigations involving nucleic acids and their components are precise calculations of the intermolecular ring current effects attributable to purines, pyrimidines, and flavines (677G). Conformations and interactions of nucleosides (6786680G) have been studies including an application of 18CN M R (6806). Metal ion interactions with adenosine triphosphate have been investigated (681G). Examination of dinucleotides (68966860) provides basic information applicable to studies of larger materials such as transfer RNA (6866-6886) and DNA (689G) which have also r e ceived attention. Phosphorus-31 N M R spectrometry is proving of increasing value in studies of biological materials. Distinction between lipid phosphates and phosphonates (690G), conformation studies of dinucleotides (69lG), examination of nucleoside phosphorothioates (69SG), and investigations of adenine nucleotides (6930) and ion complexing therewith (694G) represent recent applications to small molecules. Among large m o l e cules 81PN M R has been used to study enzyme catalyzed hydrolsyis of polyphosphates (6960) and the chemical nature of phosphorus in caseins (696G). Of particular interest in the biological area are applications of *8Na(697G) and ‘9K (6986, 6990) N M R to the study of binding and transport of these ions. Bromine81 resonance has also been used to follow anionic surfactant binding (600G). Carbon-13 continues to grow in importance and breadth of application. Much effort in this area is still directed to generating the data base that is required before routine applications can proceed. Coupling constants between 18C and hydrogen over one (601G), two (60SG), three (603G) or more (604G) bonds have been reported. Couplings between 18C and other nuclei such as IgF, 11B, 199Hg and Sn over one or more bonds (606G) and one bond coupling constants involving 14N (606G) and rhodium-103 (607G) also received attention. Chemical shift data (and various correlations or the lack thereof with structural or electronic parameters) continue to constitute the bulk of I8C N M R work. Among aliphatic compounds papers have appeared covering cyclopropanes (608G, 609G), simple aliphatic and olefinic compounds (610G614G), alcohols (616G, 616G), carbonyl compounds (617G-621 G), dioxanes (682G),piperidines (683G),and a variety of bicyclic compounds (624G-627G). Aromatic compounds which have been studied include substituted benzenes
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(698G-630G), nonalternate hydrocarbons (631G, 6JBG) , numerous nitrogenous heterocycles (633G-639G) and several sulfur containing materials (640G-649G). Biologically important materials such as terpenes (643G-6’46G), steroids (646G) , alkaloids and nitrogenous materials (647G, 648G), amino acids and peptides (6&9G-651G), sugars (66BG-656G), nucleosides (657G-669G) and nucleotides (660G) have also been investigated. Inorganic materials studied by lac N M R include carboranes (661G), metal complexes (669G-S64G), metal hydride carbonyl complexes (6650) , halonium salts (666G) , and group IV (667G) and group V compounds (6686). Applications of NMR are increasing. Carbonium (669G-676G) and carbanions (676G) have received the most attention. Studies of conformational effects on lacshifts and couplings and utilization of I3C N M R to investigate conformational problems have both appeared (677G-680G). Magnetic nonequivalence has been demonstrated (681G-683G). Intermolecular interaction energies (684G), polymer structural studies (685G), and correlations between lac (and 1 7 0 ) shifts and UV spectral transition energies represent further examples of the broad range of problems t o which IaC N M R is being applied. Practically all high resolution N M R spectra are obtained with liquid samples. Hence, the effects of solvents on N M R parameters and conversely the use of variations in N M R parameters to study phenomena of the liquid state provide a bewildering variety of literature. Central to all such studies is the development of a technique to obtain reference independent solvent shifts (687G) and new methods for utilizing external reference techniques (688G). Hydrogen bonding between alcohols and nitriles has been shown to provide a means whereby H-C-0-H coupling may be observed (6896). The super acid system [antimony pentafluoride-fluorosulfuric acid (sulfur dioxide)] has been studied (690G). Kitrogen-14 resonance has been used to investigate solvation of electrons in liquid ammonia (691G). Nitrogen-15 spectrometry has been used to examine intermolecular interactions (other than H-bonding) (6926). The average segmental motion of polyethylene glycol was found to depend on the amount of water present (69SG). Solvent effects on IaC (69CG), I g F (696G), and 170 (696G) shifts have been reported. The proton shift of dilute H20 solutions in dioxane-CDCl3 shifts downfield by 0.3 ppm when l60is replaced with ‘*O (697G). A number of papers report development of theoretical models to explain solvent effects on N M R parameters (698G-708G). Others report examples
lac
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of specific observations such as reaction field (7OQG-711G) and dispersion (7lBG, 713G) effects on chemical shifts. The most numerous of these studies report aromatic solvent induced shifts (ASIS) for solutes dissolved in benzene (714G733G) or occasionally in pyridine (734G736G). Less well recognized, but continually increasing are examples of solvent dependence of coupling constants (737G-748G). The p H dependence of NMR parameters has also been studied (749G-751 G). Among applications of N M R to investigations of liquid state phenomena are found studies of ion solvation (76BG761G) including utilization of W a and ?Li spectrometry to study those ions (76BG). Hydroxyl proton shifts have been used t o investigate various hydrogen bonding systems (763G-767G). Selfassociation of alcohols (768G-772G) and other materials (773G, 774G) has been investigated. Intermolecular hydrogen bonding complexes between different materials have been followed by proton (775G-777G), lac (778G) and l5N (779G, 780G) resonance. Non-hydrogen bonding complexes have also received attention (781G-783G). Such diverse topics as electrolytic dissociation (784G), solution thermodynamics (785G-789G) , solution (liquid) structure (790G-792G) , and micelle systems (793G-796G) provide further examples of the wide spread applicability and utilization of N M R techniques. LITERATURE CITED
GENERAL (1A) R. Lynden-Bell and R. K. Harris, “Nuclear Magnetic Resonance SDectroscopy,” Appl&on-Century-Croft‘s, New York, N.Y., 1971. (2A) P. Diehl, E . Fluck, and R. Kosfeld, Ed., “NMR: Basic Principles and Progress,” Springer-Verlag, New York, N.Y.. 1970. Vols. I and 11. (3A) B’. I. Ionin and B. A. Ershov, “NMR Spectroscopy in Organic Chemistry,” Plenum Press, New York, X.Y., 1970, 2nd ed. (4AI L. M. Jackman and S. Sternhell. “Applications of Nuclear Magnetic Resonance Spectroscopy in Organic Chemistry,” Pergamon Press, New York, N.Y., 1969, 2nd ed. (5A) W. W. Pandler, “Nuclear Magnetic Resonance,” Allyn and Bacon, Inc., Boston, Mass., 1971. (6A) R. T. Schumacher, “Introduction to Magnetic Resonance,” UT.A. Benjamin, Inc., New York, N.Y., 1970. (7A) H. Strehlow, “Nuclear Magnetic Resonance and Chemical Structure,]’ Steinkopff, Darmstadt, Germany, 1968, 2nd ed. (8A) R. J. Abraham, “Analysis of High Resolution NMR Spectra,” Elsevier, New York, N.Y., 1971. (9A) C. H. Dungan and J. R. Van Wazer, “Compilation of Reported 19F XMR Chemical Shifts: 1961 to Mid-1967,” Wiley-Interscience, New York, N.Y., 1970. (10A) G. R. Eaton and W. N. Lipscomb, “NMR Studies of B o y Hydrides and Related Compounds, W. A. Benjamin, Inc., New York, N.Y., 1969. ~
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(11A) T. C. Farrar and E. D. Becker, “Pulse and Fourier Transform NMR,” Academic Press, New York, N.Y., 1971. (12A) C. P. Poole, Jr., and H. A. Farach, “Relaxation in Magnetic Resonance,” Academic Press, New York, N.Y., 1971. (13A) J. H. Noggle and R. E. Schirme? “The Nuclear Overhauser Effect, Academic Press, New York, N.Y., 1971. (14A) F. A. Bovey, “High,, Resolution NMR of Macromolecules, Academic Press, New York, X.Y., 1971; I. Ya. Slonim and A. N. Lyubimov, “The NMR of Polymers,” Plenum Press, New York, N.Y., 1970. (15A) J. P. Heeschen, ANAL.CHEM.,42, 418R-451R (1970). (16A) Progr. N M R Spectrosc., 4 (1969). (17A) Zbid., 5 (1969). (18A) Zbid., 6 (1971). (19A) Ibid., 8 (1971). (20A) R. M. Golding, in “Physical Chemistrv.” H. Evrinn. Ed.. Academic Press, New- York, N. 1970, Vol. 4. (21A) E. F. hIooney, in “Spectrosco y,” D. R. Browning, - Ed., hlcGraw-kill, London, 1969. (22A) R. 31. Golding, “Applied Wave Mechanics,” D. Van Nostrand Co., New York, N.Y., Chap. 8. (23A) A. Chakravorty, in,,“Spectroscopy in Inorganic Chemistry, C. N. R. Rao and J. R. Ferraro, Ed., Academic Press, New York, N.Y., 1970, Vol. I, p 248. (24AI D. R. Eaton. in “Phvsical Methods in ’ Advanced Inorganic: Chemistry,” H. A. 0. Hill and P. Day, Ed., Interscience Publishers, New York, N.Y., 1968. (25A) P. J. McCarthy in “Spectroscopy and Structure of Metal Chelate Compounds,” K. Nakamoto and P. J. McCarthy, Ed., J. Wiley and Sons, New York, N.Y., 1968. (26A) C. J. Hawkins, “Absolute Configuration of Xetal Complexes,” WileyInterscience, New York, N.Y., 1971. (27A) R. Chang, “Basic Principles of Spectroscopy,” McGraw-Hill, New York, N.Y., 1971. (28A) E. F. H. Brittain, W. 0. George, and C. H. J. Wells. “Introduction to Molecular Spectroscopy, Academic Press, New York, N.Y., 1970. (29A) Ann. Rev. S M R Spectrosc., 2 (1969). (30A) Ann. Rept. ,VMR Spectrosc., 3 (1970). (31A) J. Feeney, Ann. Rept. Progr. Chem., 65 (Sect. A), 63-81 (1968) (Publ. 1969). (32A) Advan. Magn. Resonance, 4 (1970). (33A) Ibid., 5 (1971). (34A) S. V. Vinogradov and R. H. Linnell, “Hydrogen Bonding,” Van Nostrand Reinhold Co., New York, N.Y., 1971, Chap. 4; A. I. Brodskii, V. D. Pokhodenko, and V. S. Kuts, Usp. Khim., 39, 753 (1970); C. N. R. Rao and A. S. N. Murthy, Develop. Appl. Spectrosc., 7B, 54 (1968) (Publ. 1970). (35A) G. A. Webb, Ann. Repts. iVMR Smctrosc.. 3 . 211 (1970). (36A) D. E. Leyden, Cr>tical Rev. Anal. Chem., 2,383 (1971). (37A) H. J , Keller and K. E. Schwarzhans, Angew. Chem., Znt. Ed. Engl., 9, 196 (1970); K. E. Schwarzhans, i b i d . , D 946. (38A) B. Stalinski, Metody Badaw. Chem. Koordynacyjnej, 181-208 (1967); J. W. Dawson and L. 32. Venanzi, Trans. S .Y . Acad. Sci., 32, 304 (1970). (39A) G. E. Bacher- and T. Schaefer, Chem. Rev., 71, 617 (1971). (40A) RI. Barfield and B. Chakrabarti, i b i d . , 69, 757 (1969); K. D. Bartle, D. W. Jones and R. S. Jlatthews, Rev. Pure Appl. Chem., 19, 191 (1969).
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