R.A. Nyquist

INFRARED SPECTRA OF INORGANIC COMPOUNDS

This chapter discusses the experimental, theoretical, and empirical correlations between functional organic groups and the infrared spectrum. The application of infrared spectroscopy to the identification of inorganic compounds is less successful. In obtaining infrared spectra of inorganic solids, an experimental complication arises from possible chemical reaction between the inorganic compound and the infrared window material or support medium. The chapter presents many examples of spectra of inorganic compounds in the solid phase. The majority of these compounds are crystalline solids in which the crystallographic unit cell contains several polyatomic ions or molecules. Optical modes called lattice modes of vibration result from the motion of one polyatomic group relative to another within the unit cell. Lattice modes occur in the region 400–10 cm −1 and are characteristic of specific crystal geometry. They are used as fingerprints for an inorganic compound in much the same way as the internal modes of vibration of organic compounds are used in the region 4000–400 cm −1 .

Factors affecting the out-of-plane hydrogen deformation frequencies in olefins and their derivatives

Abstract The various infrared absorption group frequency correlations for out-of-plane hydrogen deformations of substituted ethylenes are reviewed. It is shown that the CH 2 wag motion of vinyl and vinylidene type substituted ethylenes behave in an analogous manner, and the twist motion in vinyl and trans -type substituted ethylenes also behave in an analogous manner. The CH 2 wag frequency appears to be related to the resonance effects of substituent groups, while the twist frequency appears to be related to the inductive effects of substituent groups.

Infrared absorptions characteristic of the terminal acetylenic group (-CC-H)

Abstract The infrared spectra of a variety of acetylenic compounds have been obtained. The behavior of various frequencies characteristic of the -CC-H group (C-H stretch, ~3315 cm−1; CC stretch, ~2130 cm−1, C-C stretch, ~930 cm−1, C-H bend, ~640 cm−, and C-CC skeletal bend ~350 cm−) are discussed. The splitting of the degeneracy of the C-H bend into two frequencies in certain cases is discussed and an explanation proposed. A correlation between the C-H deformation frequencies and certain chemical parameters is suggested.

Solvent-Induced Nitrile Frequency Shifts: Acetonitrile and Benzonitrile

The C≡N stretching frequency, vC≡N, is affected by change in the solvent and also by change in concentration in the same solvent. In the case of acetonitrile, vC≡N is in Fermi resonance with the combination tone (δsym. CH3 + vC-C), and the degree of Fermi resonance interaction changes with change in the solvent. With the exception of dimethyl sulfoxide, unperturbed vC≡N for acetonitrile exhibits a pseudo-linear correlation with the acceptor number of the solvent.

The O-H out-of-plane deformation in intramolecularly hydrogen bonded phenols

Abstract The O-H out-of-plane deformation fundamental (γO-H) occurs in the frequency region 300–860 cm−1 in various ortho substituted phenols studied. The absorption band produced is uniquely broad, and therefore easily assigned. Correlations ofγO-H with vO-H and certain chemical parameters have been found, and these are useful in explaining the frequency behaviour of this vibration. These several characteristics make this vibration useful as a “group frequency”.

Infrared absorptions characteristic of organic carbonate derivatives and related compounds

Abstract Infrared absorption bands characteristic of carbonates , carbamates , monothiolcarbonates , chloroformates , carbamoyl chlorides , thiol carbamates , dithiol carbonates , and thiol-chloroformates have been found. The behavior of these frequencies in the various compounds can be related and explained by considering the vibrations to be roughly analogous to those of the carbonyl dihalides.

Acetyl halides—I: Infrared and Raman spectra and vibrational assignment of CH3COCl, CD3COCl and CH2DCOCl

Abstract The infrared and Raman spectra of acetyl chloride, acetyl chloride-d3 and acetyl chloride-d1 have been studied and a vibrational assignment has been made on the basis of an approximate normal-co-ordinate calculation with a Urey-Bradley field. It is proposed that the two intense bands at 1109 and 958 cm−1 in the infrared spectrum of acetyl chloride correspond to vibrational modes which are mixtures of the C-C stretching co-ordinate and the CH3 rocking co-ordinate, and that the similar pair of intense bands in the CD3COCl spectrum arise from modes which are mixtures of CC stretching and CD3 deformation co-ordinates. Thermodynamic functions were calculated for acetyl chloride in the ideal gaseous state.

The vibrational spectra of the allyl halides

Abstract Infrared spectra (200–3800 cm −1 ) of the allyl halides (fluoride, chloride bromide and iodide) were obtained at temperatures from 25°C to −150°C. These data suggest the existence of two rotational isomers of each allyl halide at 25°C. Raman spectra including depolarization measurements and infrared vapor phase spectra were also obtained. Vibrational assignments based on these data are proposed.

Characteristic infrared absorption frequencies of thiol esters and related compounds

Abstract The effects of chemical structure upon the carbonyl stretching frequencies of thiol esters are discussed, and shown to be generally similar, with certain modifications, to the corresponding effects upon ordinary ester carbonyl frequencies. Other absorption frequencies, characteristic of the group in thiol esters, the group in thiol formates, the group in thiol carboxylic acids, and the group in salts of thiol carboxylic acids have been noted, and their probable vibrational modes discussed.

The structural configuration of some α-substituted secondary acetamides in dilute ccl4 solution

Abstract An infrared study of several α-substituted secondary amides in dilute CCl4 solution has suggested an explanation for the observation that these compounds contain only one carbonyl stretching absorption band, whereas analogous tertiary amides are known to exhibit two carbonyl stretching absorption bands. These conclusions have been based on infrared spectra obtained on a high resolution prism grating spectrometer. The N-H stretching frequencies and integrated intensities and the carbonyl stretching frequencies are used to explain the structural configuration. Both the N-H and CO stretching absorption bands appear to be affected, at least in part, by the inductive effect.