Downloaded by UNIV OF CAMBRIDGE on September 2, 2015 | http://pubs.acs.org Publication Date: October 1, 1979 | doi: 10.1021/j100483a020
ESR-ENDOR Study of a-D-Giucopyranose
may suggest that the magnitudes for both k , and the lifetime of adsorbed H,TPP are not significantly different from those of the solid film. We assume, therefore, that Tad is equal to a T~ of 0.31 ns. Furthermore, CP is approximated as 0.30, which is the average value for two cases. Under these assumptions, the value of k, is evaluated as k , = 7.5 X lo9 sd. We have, therefore, obtained two quantities, k , and K , which characterize the chargeinjection reaction at the interface between HzTPP and Sn02. Two possible mechanisms have been suggested for the charge-injection reaction at semiconductorsurfaces: direct injection (electron transfer) and indirect injection (energy transfer via surface states).l,12 The distance dependence of k,, or a, should give us useful information on the mechanism concerned, since k, is considered to have a different dependence on the distance for the two mechanisms.lJ3 Our results shown in Figure 4 are, however, simply qualitative,6 so we cannot distinguish which mechanism best describes the H2TPP/Sn02system from results obtained in this study. The determination of the mechanism concerned requires more sophisticated experimental studies, including more accurate measurement of the distance dependence of the reaction rate. Microscopic understanding of the rate constants obtained will be made possible by detailed information on adsorption structure, on energetic correlation adsorption, and on
The Journal of Physical Chemistry, Vol. 83, No. 20, 1979 2643
atomic and electronic structures of the surface, and these are future problems.
Acknowledgment. This work was supported by a Science Research Grant from the Ministry of Education. The authors thank Professor K. Yoshihara for his continuous encouragement and Dr. J. Hougen for his English corrections.
References and Notes (1) (2) (3) (4) (5) (6)
(7) (8) (9) (10) (11) (12) (13)
H. Meier, Photochem. Photobiol., 18, 219 (1972). E. Lendvay, J. Phys. Chem., 89, 738 (1965). K. Tanimura, T. Kawai, and T. Sakata, to be published. See, e.g., K. M. Smith, Ed., “Prophyrins and Metaiioporphyrins”, Eisevier, Amsterdam, 1975. P. G. Seyboid and M. Gouterman, J. Mol. Spectrosc., 31, 1 (1969). The value of the distance determined may not have good reliability, since it is difficult to control a distance of several angstroms in the evaporated KCI fllm. An island structure of the KCI film may result in an apparent increase of the distance at which the relative yield recovers to unity. The results shown in Figure 4 are, therefore, considered to give an upper limit for the magnitude of the distance dependence of @. F. J. Kampas and M. Gouterman, J . Lumin., 14, 121 (1976). K. Tanirnura, T. Kawai, T. Sakata, N. Nakashima, and K. Yoshihara, unpublished. E. 9. Fieisher, C. H. Miiier, and L. E. Webb, J. Am. Chem. Soc., 88, 2342 (1964). E. Ciementi and M. Kasha, J. Chem. Phys., 27, 956 (1957). W, White and P. G.Seybold, J. Phys. Chem., 81, 2035 (1977). J. Lagowski, H. C. Gatos, and C. L. Baiestra, J . Appl. Phys.. 49, 2821 (1978). H. Kuhn, J. Chem. Phys., 53, 101 (1970).
ESR-ENDOR Study of a-D-Glucopyranose Single Crystals X Irradiated at 12 and 77 K K. P. Madden” and W. A. Bernhard Department of Radiation Bioiogy and Biophysics, School of Medicine and Dentistry, The University of Rochester, Rochester, New York 14642 (Received April 16, 1979) Publication costs assisted by the National Science Foundation and the U.S. Department of Energy
Single crystals of anhydrous a-D-glucopyranoseX irradiated at 12 and 77 K contain four free-radical species: two secondary alkoxy radicals centered at 0-2, a primary hydroxyalkyl radical centered at (2-6, and a secondary hydroxyalkyl radical centered at C-3. Structural considerations are discussed, and the radicals compared with four radicals found in single crystals of a-D-glucopyranosideX irradiated under similar conditions.
Introduction Our laboratory has recently engaged in a study of the radiation chemistry of simple sugars in the solid state. The information gained from these systems helps to elucidate the radiation chemistry of carbohydrates and to predict possible free-radical alterations induced in the deoxyribose moiety of DNA. In a recent paper,l four major free-radical species have been identified in single crystals of amethyl-D-glucopyranoside(aMeGlu) X irradiated at 77 K. aMeGlu is a methylated derivative of anhydrous a - ~ glucopyranose (aGlu), shown in Figure 1. In this present work, four free-radical species in aGlu have been identified, allowing for a comparison of the free-radical processes and products occurring in these two systems. Glucose has been studied with ESR in various phases (polycrystalline, frozen solutions, syrups) by a number of investigators.2-8 In these systems, it is often difficult to obtain unambigous assignments since one cannot readily
distinguish between a number of similar radical species. Study of simpler single crystal spectra provides more definitive information on the interactions of the unpaired electron with the glucosyl radical environment. The resolution of the ESR data has, for several radicals in this work, been enhanced with ENDOR information. The accuracy of these data is sufficient to allow the comparison of free radicals in aGlu with the closely related aMeGlu system.
Experimental Section Anhydrous a-D-glucose was obtained from Fisher Scientific, and used without further purification. Crystals of aGlu were grown by preparing a saturated aqueous solution, followed by seeding and slow cooling. The entire process of crystal growth occurred above 55 “C, so that the anhydrous form of the crystal would be p r o d ~ c e d . ~ Crystals thus grown were found to be orthorhombic, of
0022-365417912083-2643$01.0010 0 1979 American Chemical Soclety
2644
The Journal of Physical Chemistty, Vol. 83, No. 20, 1979
K. P. Madden and W. A. Bernhard
OH I
aGLUC
H- C r H I I
n
r
k
bH
I
OH I
H- C,-H
otMeGLUC
Downloaded by UNIV OF CAMBRIDGE on September 2, 2015 | http://pubs.acs.org Publication Date: October 1, 1979 | doi: 10.1021/j100483a020
I
k
bH
Figure 1. Structures of a-D-glucopyranose and a-methyl-D-glUCOpyranoside.
space group P212121, with four molecules per unit cell. Crystals were also grown from deuterium oxide, to convert OH groups to OD. The starting material was recrystallized several times from deuterium oxide to dilute out the light protons. aGlu-6,6-d2was obtained from Stohler Isotope Chemicals and used without further purification. Crystals were aligned along their axes by using the Buerger precession method, and were transferred to a copper pedestal for X band studies (ESR and ENDOR). The total error in this process is known to be less than 0 . 5 O . Irradiations were performed at 77 and 12 K, using 50-kV X rays at a dose rate of 1.5 Mrd h-l for 2.5 h. ESR studies were done with a Varian E-12 spectrometer, using a modified version of the cryotip cavity developed by Weil et al.1° ENDOR studies were performed in the cryotip cavity, with the addition of a loop of wire to produce an intense magnetic field perpendicular to the static magnetic field, Ho, and the microwave magnetic field, H1. The electronics and method of data collection used in the ENDOR experiment were described in ref 11. Both ESR and ENDOR data were recorded in planes perpendicular to the three crystallographic axes at 10" intervals in each plane. G tensors for the oxygen-centered species were calculated with a non-linear least-squares method. Raw data for g factor evaluation were ESR spectra, with the magnetic field values taken from the spectrometer, and the klystron frequency monitored by a Hewlett-Packard Model 52451, frequency counter with 5257A transfer oscillator. Final calibration of the g factors was performed by peak of the species I11 (see below) comparing the ,g powder spectrum with a DPPH marker. Hyperfine coupling tensors from ENDOR data were derived by using a two-step technique of trial tensor generation by Schonland's method,12 followed by a non-linear leastsquares fit to the actual ENDOR data.13 After determination of hyperfine coupling tensors for each radical species, the principal axes were compared with possible radical loci in the undamaged molecule with a modified version of the X-ray crystallography program 0RFEE3.l4 The atomic positions used were from the neutron diffraction study of Brown and Levy, which lo-
IV
I
I1
4
I
U
Flgure 2. 77 K X-band first-derivative ESR spectra of aGlu with H, parallel to ( b ) (top) and H, parallel to ( c ) (bottom). Lines for species I, 11, 111, and I V are shown.
cated the hydrogen positions to 0.006 A.16
Results, Analysis, and Free-Radical Models The ESR spectra along crystallographic axes (Figure 2) indicate the presence of four free-radical structures. Species I. This species is the major product in crystals
YH
P-C.
I
-C
0
H
OH
I grown from D20 or H20. It is characterized by a nearly isotropic g factor and three hyperfine couplings (hfc): one typical of an a proton, one typical of a 0 proton, and a small coupling ranging from 21 MHz along the a axis to -0 MHz along the c axis. The latter hfc collapses upon deuteration of the labile protons in the crystal. Table I contains the hfc tensors and Figure 2 illustrates the fit between the data and curves predicted by the tensors. The a hydrogen isotropic hfc of 57.8 MHz can be used to estimate the carbon 2p unpaired electron density, p, by employing McConnell's equation AimH== PQ
(1)
With Q = 64 MHz, one obtains p = 0.90. A scan of the native molecule yielded two likely assignments for a free radical with an a proton, 0 proton, and hydroxyl hfc: HOC,HC,H< or HOC,HC,HCH-0 and/or >C-OR radical associated with it. If a particular radical is not observed with
ESR-ENDOR Study of a-D-Glucopyranose
The Journal of Physical Chemistry, Vol. 83, No. 20, 1979
TABLE 111: 0-2-Centered Radicals principal value
principal axes Species I11 2.0614 -?I 0.0008 (-0.274, 0.915, -0.296) 1.9998 t 0.0008 (-0.95, -0.31, -0.07) 1.9952 i 0.0008 (+0.16, -0.26, -0.95)
A$@
6( -?I l ) , b 24( c l)e 7(+6) 40(T$)f 61( t 7),d 38(1::)g
2.0188 266 MHz
-
2h
2647
6’ in aMeGlu vs. 54” in aGlu. As hyperconjugation increases, the proton retaining bond would weaken. Second, the hydrogen bonding environment of O6 differs in aMeGlu. An “extra” hydrogen bond from O4 exists in aMeGlu but not in aGlu. Thus, Os in aMeGlu is in a better proton accepting environment than O6 in aGlu. The hydrogen bonding environment is also likely to be a factor in explaining why the oxyl radical O6 is not observed in aGlu but is observed in aMeGlu. In both crystals O6 partakes in an infinite helix of hydrogen bonds, shown in IIIA. So in each crystal, Os is a strong hydrogen bond
Species IV 2.0563 + 0.0008 (-0.15, 0.876, 6( i l),b -0.457) 25( c l)e 2.0061 -?I 0.0008 (-0.835, 0.132, 0.53) 1.9810 t 0.0008 (+0.53, 0.464, 0.711) 43(i2),c 21( c 2)f 1(i l ) , d 23( i 2)g 2.0145 224 MHz 25’ Downloaded by UNIV OF CAMBRIDGE on September 2, 2015 | http://pubs.acs.org Publication Date: October 1, 1979 | doi: 10.1021/j100483a020
a
-x.
As in Table I.
i (C,-O,.
*
.Os’).
1 ((3,-
0,. . eo,”). e c,-0,. f 1 (C,-O,* . .O,“’). g 1 ((2,-0;’ 0,- . .O,“’). Difference between crystallographic torsion angle i (C,-O,. . .O,‘)-0,-C,-H, and measured torsion angle, using eq 1 with Bo = 0 mT and B , = 10 mT. Difference between crystallographic torsion angle 1 ((3,-0; . .O,’)-0,-C,-H, and measured torsion angle, using eq 1 with B o = 0 mT and B , = 10 mT.
.
ESR, it generally means that its concentration is at least two orders of magnitude lower than that of the observed species. The low concentration of these radicals can be attributed to (1)lower G value (yield), (2) higher radiation destruction, or (3) reactions leading to a diamagnetic end product. Since little is known of radiation destruction of radicals, and since the diamagnetic end products produced from radicals are invisible in an ESR study, we shall concentrate on structural features around a given oxygen atom which might tend to stabilize an incipient hydroxyalkyl or alkoxy radical. Not present in the model outlined above are excitation pathways or reduction events resulting from electron capture. This is partly for simplicity; but two further observations argue for an oxidation based model. Box and colleagues18have observed trapped electrons in carbohydrates and polyalcohols, using ESR. Upon warming these disappear without giving rise to new ESR signals, suggesting the final product is diagmagnetic, not available to experimental observation with ESR. Also, hydroxyalkyl and alkoxy radicals have been found in materials containing excellent electron traps, such as nucleosides and nucleotides. In spite of the electron scavenging efficiency of the bases in these systems, both of these species are often present. We now consider each oxygen in aGlu, its possible fates after ionization, and the free-radical products observed in aGlu and aMeGlu. Ionization at Os Reaction 4 appears operative in both aGlu and aMeGlu. However, in aMeGJu the hydroxyalkyl radical deprotonates to give HC60- instead of HC60H. Formation of an hydroxyalkyl radical is known to lower the pK, of so the hydroxyl proton by about 4 units, from 16 to deprotonation in the center is not surprising. However, why does deprotonation occur more readily in aMeGlu than aGlu? Two factors seem important. First, the torsion angle between the LEO symmetry axis and OH bond is
E B donor and strong hydrogen bond acceptor. After ionization of O6the O2(H).-O6 bond will cause the LEO to lie normal to the C6-06.-(H)02 plane, leaving the LEO in a configuration that tends to maximize the torsion angles between the LEO and the two C-H, bonds (IIIB). This is an unstable configuration, and in aMeGlu there is a 53’ reorientation to compensate for this instability.20 This reorientation in aMeGlu is made possible by the extra hydrogen bond between O4and Os, allowing the reoriented oxyl radical to minimize the torsion angles between the LEO and the CH, bonds. In aGlu O4 partakes in an infinite chain of 04(H)-04(H) hydrogen bonds; this option is therefore not available. These two factors, tending to destabilize primary alkoxy radicals in aGlu, could operate in two ways: (1)formation of the primary alkoxy is retarded because O4is not available to function as an extra proton acceptor, or (2) the instability of a formed alkoxy radical is so great that abstraction of the neighboring hydroxylic proton, HoW2, becomes an energetically favorable event (IIIB IIID or IIIE). Mechanism 1 is supported experimentally by the existence of an isotope effect in aMeGlu, where crystals deuterated at O6 show an enhanced [hydroxyalkyl radical] / [primary alkyoxy radical] ratio, relative to protonated crystals, implying deuteration promotes reaction 4 at the expense of reaction 5. Mechanism 2 provides one possible explanation for the presence of two types of O2radicals in aGlu, discussed below. -+
Ionization at O2 The secondary alkoxy radical, 02,is observed in both aGlu and aMeGlu; but, only in aGlu are there two distinct
Downloaded by UNIV OF CAMBRIDGE on September 2, 2015 | http://pubs.acs.org Publication Date: October 1, 1979 | doi: 10.1021/j100483a020
2648
K. P. Madden and W. A. Bernhard
The Journal of Physical Chemistry, Vol. 83, No. 20, 1979
O2radicals. Formation of both I11 and IV can be explained by either direct ionization at O2or an indirect pathway via hydrogen abstraction by 06.If IVA is formed by ionization at 02,the hydroxylic proton must be ejected from the hydrogen bonding network about 02. Capture of the proton by O6would give IVB. Alternatively, an O6 radical IIIB or IIIC could abstract a hydrogen to give IIID. With partial or full reorientation of the new H-O6 bond, as in IIIE, this center could resume a structure magnetically indistinguishable from IVA. The greater stability of I11 over IV and the observed direction of gmincause us to prefer IIIE as an assignment for species I11 and IVB for species IV. The gmhdirections, as analyzed in the Results section, add sway to the idea that the lone pair will be stabilized by the strongest hydrogen bond. These results also point out a need for caution in trying to predict the direction of gminbecause the relocated hydroxylic proton may influence the direction drastically. In IV the relocation results in a predictable geometry but relocation to other positions around the oxygen would result in a gminnot readily predicted from either of the two original hydrogen bonds. As another example of this process, we would like to note that in deoxyadenosine the proton relocation for the primary alkoxy radical appears to be analogous to that of species IV. Ionization at O3 The hydroxyalkyl radical, >C3-OH, but not the alkoxy radical, >C3(H)0, is observed in aGlu. In aMeGlu the situation appears to be the same, though identification of >C3-OH is not as clear cut. According to the model, this means reaction 4 dominates in the decay of the O3 cation, in contrast to the dominance of reaction 5 in the decay of the O2 cation. Why does >CH02H+ deprotonate at OH while >CH03H+deprotonates at CH? One difference lies in the surroundings of the methylene hydrogens, Hc.2 and HC.3. are both axial to the pyranose ring, but Hc.2 Hc.2 and HCm3 is on the top side of glucose while HCS3is on the bottom side. (We define the top side of aGlu and aMeGlu as the side of the pyranose ring containing the c6 primary alcohol group.) This puts Hc.z amid the C-H rich side of the molecule while HC-3is in a C-0 rich environment. The more polar environment of HC.3may promote reaction 4 over reaction 5 while the less polar Hc.z environment may retard reaction 4 relative to reaction 5. Ionization at O4 In aGlu and aMeGlu no free radicals observed can be assigned to decay of an O4 cation. In both systems, the ~ both surroundings of O4has poor proton acceptors. H C . in systems is on the top side of the pyranose ring; the relatively nonpolar environment is a poor proton acceptor. In aMeGlu, the HG4is only weakly bonded to the primary alcohol group, minimizing its ability to stabilize an incipient deprotonation event. In aGlu H o - ~is hydrogen bonded to 0-4 in the adjacent molecule, but, still, alkoxy radical formation does not occur. In lieu of radical production, we postulate the ionized O4 proceeds to a diamagnetic end product, most likely by loss of an H atom or electron tunneling. Ionization at O5 The O5 cation can deprotonate at either C1 or C5, In aMeGlu the c5radical is a major product and we presume reaction 6 is the main pathway of formation at temperatures between 12 and 77 K. H5 is on the bottom side of aMeGlu and is a likely deprotonation site for an O5 cation.
el
Also observed in aMeGlu is the radical, a possible product of either O5 or O1 ionization, followed by deprotonation at HI. H1 is on the top side of the pyranose ring, but is distingujshed by being on the anomeric carbon. In aGlu neither C5 nor C1 is observed. Here aGlu being a hemiacetal while LvMeGlu is an aceta1.k likely to play a role. The hemiacetal allows for either C1 or C5 to decay by eliminating a hydrogen atom, as in reaction 7.21 Rl
\
I
C-OR
-
R,
\
I
C=OtR
(7)
RZ RZ R = H (hydroxyalkyl) = CH(0H) (hemiacetal) = C H ( 0 R ' ) (acetal)
Hydrogen atoms can recombine or abstract methylene hydrogens, thereby erasing any free-radical signature of the O1 ionization.
Summary Under our working model ionization at O6leads to both a primary hydroxyalkyl radical and primary alkoxy radical, ionization at O2leads predominantly to a secondary alkoxy radical, ionization at O3 leads predominantly to a secondary hydroxyalkyl radical, and ionization at O5leads to deprotonation at either C5or C1. These radicals have been identified in single crystals of aGlu and aMeGlu, and the effects of the environment on the free-radical chemistry have been noted. Acknowledgment. The authors thank those who helped us in this study: Professor Andrew Van Hook, of the College of the Holy Cross, who gave us aGlu crystals used to begin this study, along with helpful advice on glucose crystallization; Mr. Kermit R. Mercer, for technical assistance beyond compare; Dr. George W. Fouse, for the development of the computer programs used in this study; and Mr. Robert Spalletta, for many helpful discussions. One of us (K.P.M.) gratefully acknowledges a fellowship from the University of Rochester Department of Radiation Biology and Biophysics, and support from Florence H. Madden. This work was performed under contract with the U.S. Department of Energy at the University of Rochester Department of Radiation Biology and Biophysics (assigned Report No. UR-3490-1603),and partially under NSF Grant No. PCM77-16830.
References and Notes (1) K. P. Madden and W. A. Bernhard, J. Chem. Fhys., 70, 2431 (1979). (2) A. J. Bailey, S. A. Barker, J. S. Brimacombe, D. Pooley, and D. H. Spence, Nature (London), 190, 259 (1961). (3) M. A. Collins, Nature (London), 193, 1061 (1962). (4) S. Dilli and I. L. Garnett, Nature (London), 198, 984 (1963). (5) J. Bardsley, P. J. Baugh, and G. 0. Philllps, J. Chem. Soc., Perkln Trans. 2 , 614 (1975). (6) P. J. Baugh, K. Kershaw, and G. 0. Phlllips, J. Chem. SOC.B , 1482 (1970). (7) I. E. Markov, 8. G. Ershov, and A. K. Pikaev, Bull. Acad. Sci. USSR, Div. Chem. Sci., 21, 95 (1972); ibid., 21, 106 (1972) (In Russian). (8) 0.0. Phillips, Radiat. Res. Rev., 3,335 (1972), and references Wein. (9) A. Van Hook, private communication. (10) J. Weil, P. Schindler, and P. M. Wrlght, Rev. Scl. Instrum., 38, 659 (1967). (11) D. M. Close, G. W. Fouse, and W. A. Bernhard, J. Chem. fhys., 88, 1534 (1977). (12) D. S. Schonland, Proc. Phys. SOC. London, 73, 788 (1959). (13) G. W. Fowe, Jr., and W. A. Bernard, J. Ma@. Reson., 32, 191 (1978). (14) W. R. Busing, G. 0. Martin, and H. A. Levy, ORFFE, a Fortran Crystallographic Function and Error Program, ORNL-TM-306 (1964). Modified by G. M. Brown, E. K. Johnson, and W. E. Thiessen, ORFFE~, Oak Ridge National Laboratory, Oak Rldge, Tenn. (1971). (15) 0.M. Brown and H. A. Levy, Science, 147, 1038 (1965). (16) W. A. Bernhard, D. M. Close, K. R. Mercer, and J. C. Corelll, Radkf. Res., 88, 19 (1976).
13C NMR of Mirex
The Journal of Physical Chemistry, Vol. 83, No. 20, 1979 2649
(17) W. A. Bernhard, D. M. Close, J. Hbttermann, and H. Zehner, J. Chem. Phys., 67, 1211 (1977). (18) H. C. Box and E. E. Budzinski, J. Chem. Phys., in press. (19) K. Eiben and R. W. Fessenden, J . Phys. Chem., 75, 1186 (1971).
(20) K. P. Madden and W. A. Bernhard, unpublished results. (21) M. Dlzdaroglu, D. Henneberg, K. Neuwald, G. Schomburg, and C. von Sonntag, Z . Nafurforsch. S, 32, 213 (1977), and references
therein.
Effects of Solvent and Charge-Transfer Complex Formation on the I3C NMR Spectrum of the Pentacyclic Chlorocarbon Mirex Nancy K. Wilson Health Effects Research Laboratory, US. Environmental Protection Agency, Research Triangle Park, North Carollna 277 I 1 (Received February 20, 1979)
Downloaded by UNIV OF CAMBRIDGE on September 2, 2015 | http://pubs.acs.org Publication Date: October 1, 1979 | doi: 10.1021/j100483a020
Publication costs assisted by the U.S.Environmental Protection Agency
Formation of a charge-transfer complex between the pesticidal chlorocarbon Mirex (1,1a,2,2,3,3a,4,5,5,5a,5b,6-dodecachlorooctahydro-1,3,4-metheno-l~-cyclobuta[c~]pentalene) and amines has been postulated as a mechanism for the photodegradation of Mirex in the environment. Carbon-13nuclear magnetic resonance (NMR) was used to monitor the interactions of Mirex with diethyl- and triethylamine and with various solvents. Significant correlations were observed between the 13Cchemical shifts of all Mirex carbons and amine concentration or Gutmann donor number of the solvent. The 13C NMR data showed formation of a Mirextriethylamine charge-transfer complex with K = 2.5 L mol-'. With dipole moment and dielectric constant of the solvent,there is no correlation for the Mirex dichloromethylene carbon chemical shift, but there is a significant correlation for the chemical shifts of the other two sets of carbons. Those two positions are also the positions at which photoreaction occurs for Mirex in hydrocarbon solvents. Solvent effects on 13CNMR chemical shifts may thus be useful in prediction of the exact sites of photochemical reactions in the molecule and in the prediction of the resultant photoproducts.
The pesticidal chlorocarbon Mirex (1,1a,2,2,3,3a,4,5,5,5a,5b,6-dodecachlorooctahydro-1,3,4-metheno-lHcyclobuta[cd]pentalene), 1, is a very stable compound
TABLE I: Carbon-13 NMR Chemical Shifts (6 ) of Mirexa solvent chloroform-d pyridine-d benzene-d 1,2-dibromoethane-d, dimethyl-d, sulfoxideb dime thylformamide ethyl acetate 1,4-dioxane cyclohexane tetrahydrofuran hexamethylphosphoramide triethylamine diethylamine
C-2,5
C-la,3, C-1,3a, 4,5a 5b,6
91.81 92.14 92.23 91.22 91.20 92.23 92.57 92.94 91.11 92.56 92.04
82.65 83.00 83.11 82.09 81.98 83.01 83.44 83.81 83.30 83.39 82.80
76.71 77.08 77.19 76.13 76.12 77.14 77.52 77.89 71.47 77.48 76.90
92.35 92.45
83.20 83.31
77.29 77.39
a 11%(w/v) solutions, except as noted. lution.
1
which has been widely used in the southern United States. Because of its inertness and its resistance to.environmental degradation, with resultant possible incorporation into the food chain, much work has gone into development of Mirex formulations which will decompose rapidly after application. Alley and his co-workers have shown1 that Mirex degrades photochemically in the presence of diethyl- or triethylamine to mono- and dihydro photoproducts. On the basis of a charge-transfer band in the ultraviolet (UV) absorption spectrum of Mirex in triethylamine solution, they hypothesized the formation of an amine-Mirex charge-transfer complex, analogous to the well-known charge-transfer complexes formed between chloroform and
Saturated so-
secondary and tertiary alkylamines.2 NMR chemical shifts are quite sensitive to subtle changes in the electron distribution in the m ~ l e c u l e . ~ These chemical shifts should thus be an effective monitor of molecular participation in charge-transfer complex f~rmation.~ In this study, the 13C NMR chemical shifts of Mirex were examined as functions of concentration of diethyland triethylamine and as functions of several solvent parameters: dipole moment, dielectric constant, 2 value: and donor number.6 We were interested not only in the general effects of charge-transfer complex formation on 13C chemical shifts but also in whether differences in complex formation at different carbons would show up in the NMR data.
This article not subject to US. Copyright. Published 1979 by the Amerlcan Chemical Society
