REVIEW OF FUNDAMENTAL DEVELOPMENTS
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ROBERT C. GORE,
Research Division,
Stamford Laboratories, American Cyanamid Co., Stamford, Conn.
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H I S Ijienniul review has bee11 niatlc critiwl rather than as comprehensive as the earlier r e v i e w (17 ) . The omission of any article niust be taken as reflecting the limitcd i n t e ~ w t sof the author of the review rather than the uiiimport:ince of the article. Sirice the 1954 review, several important meetings have been hc~ldboth in this count] rid abroad. An outstanding one was thr. Gordon Conference on infrared Spectroscopy held a t Meriden, S . H., during the week of August’ 2, 1954. Another similar conference is being planned for this year arid it is hoped that many important foreign infrared spectroscopists will be able t o attend. Tlie arinu:tl Ohio State University Symposium and the Pittsburgh Conference continued t o attract many persons interested in molei-nl:ir structure and annlysis. At least three universitiesllnssachusetts Institute of Technology, Brooklyn Polytechnic institute, and Fisk University-held special summer courses on t h r subject. The European Molecular Spectroscopy Group met at Uxford, July i t o 11, 1955, and heard over 80 papers. A nuniher of revielr-s on infrared spectroscopy lr-ere published dui,iiig the 2-?-ear interval in many jourrials other t,han in those appenling t o the professional spectroscopist. These have served t o acquaint specialists in other fields with the utility of spect r o ~ c . o p ~ --411 . outstanding set of reviews on near-infrared specti.owopy ( 2 1 ) h:is been published by &ye. This region has t)wn neglected sirice the first quarter of the century and is now :ig:tiri coming into its proper place because of its distinct eel1 size at1v:tritages. Tlie advent of modern instrumentation such as the 13r(-l;maii Dii arid Warren Spectracord will enhance the applicatioti of this region which fell into disuse when rock salt prisms t)cc.:ime gcrierally obtainable. Kaye discusses spectral identification, analytical application?, instrumentation, and techniques n.itti many references t o the literaturc. Anyone contemplating LIFV of thi? specinl region niust read these reviews. Tlie books or sections of ~ I O O ~published S on the subject during tlirl past 2 years include Bellamy’s ‘.Infrared Spectra of Comples ~Iolecules”( d ) , which is an excellent survey on the determination of rhcmiral structure. Thi!: should be on the desk of every chemist who is interested in the m e of infrared spectroscopy as an aid i i i strwtiire identification. i t is not a ratalog of spectra, hut reviews the literature on spectra-structure correlations. ;\Iizusliima’s “Structure of llolecules” ( 2 5 ) deals with internal rotation in organic niolccules as well as with the principles and experimental methods of structure determination. Kormal vibrat i m s are also discussed. I3ak hns written an introduction t o molecular spectra ( 1 ) which gives a good treatment of its suhject matter for beginning thcoreticnl chemists and physicists, but has little practical spectroscopy for the industrial spectroscopist. \\%on, Decius, and Cross have written the definitive t e s t on molecular vibrations ( 3 7 ) , which should be in every spectrographer’s library, even though his primary interest may be pract i d rather than theoretical.
cter w i t h very rapid prism interchange. Beckman has introd u c d a relatively inexpensive instrument \r-ith slit control$, so t h a t almost per cent transmittance spectra can be obtained. Perkin-Elmer has improved its l l o d e l 21 and offered an intensity integrating device for this instrument. I n the near future grating instruments using the Nerton-Sayee, British Sational Physical I,aboratory, type of inexpensive gratings (11) should find n-ide
use (15). -A number of papers appeared on the use of t h e potassiuni bromide pellett technique for sample preparation. Kirkland ( 2 2 ) has made a critical study of the technique in quantitative applications and finds t h a t the precision compares favorably with t h a t in liquid phase techniques. For most qualitative analysis this revie\\-er feels t h a t the disadvantages of absorbed water or special handling; the consumption of time in disk preparations: and the cost of die replacement, equipment, and optical quality potassium bromide as compared with these factors in mineral oil or hesachlorobutadiene mull techniques make the latter techniques those of choice for 99% of sample preparation. Two papers worthy of thought and of general interest t o all workers in infrared spectroscopy should be noted. T h e first, b y Giese and French ( 1 6 ) , deals with the analysis of overlapping spectral absorption bands b y derivative spevtrophotometry, They show t h a t when a band of low intensity overlaps one of higher intensity the detection of the weaker band can be greatly facilitated hj- measiiring the first derivative of the absorption curve z’s. the wave length. This may be of value in many instances of overlapping. T h e second paper offers an interesting solution t o the absorbance-optical density nomenclature dispute. Stevens suggests t h a t the unit of attenuation, the decibel, may be used in optics as well as acoustics (33). This reviewer has enjoyed the startled looks when he has told organic chemists t h a t their compound had a 7.5-decibel absorption at 1736 cm.-’ With the current. popularity of hi-fi it should be possible to find more people acquainted with the unit of attenuation than with absorbance or optical density. -An important, application of microspectroscopy t o doublebeam null-type instruments has recently been made by Blout (6). Microspectroscopy has been confiiied mostly t o use with singlebeam or ratio-recording instruments, but Blout shon-s t h a t it may easily be adapted for use with the common null instruments. REFLECTION SPECTRA
Jncquez arid his coworkers ( I n ) have madr a study of integrating spheres for use in the near-infrared. i t was found that a combination of coatings allows the measurement of reflectance x i t h an accuracy 11-ithin 1%. There has been a need for such measurements of diffuse reflectance for some time in the nearinfrared, in connection with both medical problems and the plastics field. SURFACE CHE.\IISTRY
IUSTRUlIEUTATlON A\D TECHNIQLES
A number of papers have appeared in the past 2 years showing the application of spectroscopic methods t o the study of chemisorption. Eisrhens and coworkers ( 1 2 ) in connection with cata-
There have been no revolutionary changes in instrumentation dui ing tbc period Baird has offered :t redesigned spectrophotoni577
ANALYTICAL CHEMISTRY
578 lyst studies have studied chemisorbed ammonia and carbon monoxide. Their techniques may be used to advantage by other workers interested in catalysis.
merce, has published an extremely valuable but anonymous bulletin on the spectra of plastics and resins ( 2 8 ) ,which should be in every spectrographic library. The chemistry of the plastics and resins as well as the spectra is discussed in detail.
QUALITATIVE ANALYSIS
T h e interest in the application of infrared spectroscopy to qualitative analysis and determination of structure is certainly increasing. The number of papers is so large and so varied in content t h a t it is impossible to mention them individually, The studies on collections of compounds are also increasing and are of great value both in identification and in spectra-structure correlations. If the journals still accepted spectra for publication, these studies would be of much greater value to practicing spectroscopists. Minkoff, JT‘illiams, and Mosher’s (24, 36) collection of hydroperoxides and peroxides, Childers and Struthers’ ( 8 ) sodium salts of organic acids, and Ramachandran, Epp, and McConnell’s (31 ) phenylhydantoins of amino arids have all been of great utility. Corbridge and Lowe ( I O ) have extended the existing work on phosphorus compounds to the inorganic field. The important 1%-orkof Saves, Lecomte, and coworkers ( 2 7 ) in the essential oil field should be available to everyone interested in this class of material. Spectra are used to characterize the compounds obtained from separations and chemical work. HYDROGEN B 0 h DIh G-CHELATION
A quantitative approach to the study of this phenomenon has been made by Tsubomura ( 3 5 ) , \vho finds that the frequency, shape, and molecular extinction coefficient of the OH bond in phenol are not changed by the concentration of the proton acceptor. Barrow (3)has also made extensive measurements of the intensities of hydroxyl bonds. Ferriso (14) and Hornig have extensively studied the structure of the oxonium ion, which should be of interest to anyone studying hydrogen bonding. IIargoshes and coworkers (26) have found in the crystalline state that there is a linear frequency-distance relationship for straight hydrogen bonds, 6 hile bent bonds show greater deviation, with the frequencies always higher. Increased interest in chelation and coordination compounds is shown by the appearance of a t least seven papers during the past 2 years. Those interested should look up the work of Sheppard, Bellamy, Martell, Quagliano, Fernelius, and Wiberley. BIOLOGICAL
Jones (20)has summarized 460 absorption bands characteristic of specific molecular structure in steroids, including about a hundred group frequencies recently identified but not previously reported. Cole ( 9 ) has reviewed the status of spectra-structure correlations in the steroid field very thoroughly. Steroid workers will find great value in these two papers. Thomas and coworkers (34) have done interesting work on the examination of nervous tissue and the identification of microorganisms. I n the latter case the difficulties of the standardization of the technique, IT-hich appears to be of prime importance, are discussed. This reviewer feels that the identification of bacteria by infrared spectroscopy needs much more work.
ABSORPTION INTENSITIES
Thompson (23), Crawford ( 6 ) , and their coworkers are publishing the results of their studies on band intensities. Both have shown an interest in bond polar properties in relatively simple molecules and the former has empirically studied homologous series, finding some regularities in more complex molecules of interest to chemists. Gunthard (18) has studied intensities in chain molecules. THEORETIC.AL AND MOLECULAR
The number of papers published with a theoretical or molecular structure interest is exceedingly large. It is impossible to begin to cover the important papers because of the wide variety of interests of the authors. The work of Hornig (SO) and Pimentel ( 2 9 ) on solids, Lord (2) on ring structures, and Sheppard ( 7 ) on rotational isomerism is among the series of papers that should be especially mentioned. Anyone having an interest in a specific molerule should search the literature in order to find if that molecule has been studied. LITER4TURE CITED (1) Bak, B., “Elementary Introduction of llolecular Spectra,” Sorth-Holland Publishing Po., Amsterdam (1954). (2) Baker, A. IT.,Lord, R.C., J . Chem. P h y s . 23, 1636 (1955). (3) Barrow, G., J . P h y s . Chem. 59, 1129 (1955). (4) Bellamy, L. J., “Infrared Spectra of Complex lIolecules,” TViley, New York (1954). (5) Blout, E. R., J . O p t . SOC.A m e r . 45, 1028 (1955). (6) Brooks, W.V. F., Crawford, B. L., Jr., J . Chem. P h y s . 23, 363 (1955). ( 7 ) Brown, J. K., Sheppard, X . , T r a n s . Faraday Soc. 50, 1164 (1954). . 27, 737 (1955). (8) Childers, E., Struthers, G. IT., i l r a ~CHEX. (91 Cole. A. R. H.. Reo. Pu7e and A n d . Chem. 4. 1 1 1 (19541. Corhridge, D. E. C., Lowe, E. J , ; j , Chem. Soc. (1954), 493,4555. ( 1 1 ) Dew, G. D., J . Sci. Instr. 30, 229 (1953). (12) Eischens, R. P., J . Chem. P h y s . 22, 1786 (1954). (13) Elliott, A., Proc. R o y . Soc. ( L o n d o n ) A226, 408 (1954). (14) Ferriso, C., Hornig, D., J . Chem. P h y s . 23, 1464 (1955). (15) Gaunt, J., J . Sci. I n s t r . 31, 315 (1954). (16) Giese, A. T., French, C. S.,A p p l . Spectroscopy 9, 78 (1955). (17) Gore, 11. C . , -4NAL. CHEM. 26, 11 (1954). (18) Gunthard, H., Primas, €1.. Helr. C h i m . A c t a 38, 1254 (1955). (19) Jacquez, J., llcKeehan, W.,Huss. J., Dilnitroff, J., Kuppenheim, H., J . O p t . Soc. A m e r . 45, 781 (1955). (20) Jones, R. N., Herling, F., J . Org. Chem. 19, 1252 (1954). (21) Kaye, W.,Spectrochim. A c t a 6 , 257 (1954); 7 , 181 (1955). (22) Kirkland, J. J., ANAL.CHEM.27, 1537 (1955). (23) hIills, I. AI., Thompson, H. IT., Proc. R o y . SOC. ( L o n d o n ) A228, 287 (1955). (24) Minkoff, G. J., Ihid., A224, 176 (1954). (25) hIizushima, S., “Structure of Molecules and Internal Rotation,” Academic Press, Yew York (1954). (26) iiakamoto. K., hlargoshes, AI., Rundle, R. E., J . Am. Chem. Soc. 77,6480 (1955). (27) iiaves, Y.-R., Lecomte, J., Bull. SOC. chim. (1954),966; (1955), 792, 1479.
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(28) Office of Technical Services, U. S.Dept. Commerce, P B 1 1 1, 438, POLYMERS
Rugg, Smith, and Bacon (52) have shown that the structural changes produced in polyethylene by heat oxidation are different from those effected by photo-oxidation. Rugg has found some production of hydroperoxide by heat oxidation as well as the production of different kind8 of carbonyl groups. Elliott (13) has continued his excellent work on polypeptides, showing the presence of folded and extended forms through the use of polarized radiation. The Office of Technical Services, C. S. Department of Com-
(1964). (29) Pimentel. G. C., J . Chem. P h y s . 23, 234 (1955). (30) Plumb, R. C., Hornig, D. F., Ibid., 23,947 (1955). (31) Ramachandran. L. K., Epp, A, LIcConnell, W. B., -412.4~. CHEX 27, 1734 (1955). (32) Rugg, F. AI., Smith, J. J., Bacon, R. C., J . Polymer Sci. 13, 535 (1954). (33) Stevens, S. S., Physics T o d a y 8, 12 (1955). (34) Thomas, L. C., Spectrochim. A c t a 6 , 320 (1954). (35) Tsuhomura, H., J . Chem. P h y s . 23,2130 (1955). (36) Williams, H. I{., llosher. H. S., -%N.
