C—H Out-of-Plane Bending

FIGURE 2.35. Pyridine. Aromatic C—H stretch, 3090-3000 cm-1. C—C, C—N ring stretching (skeletal bands), 1600-1430 cm-1. C—H out-of-plane bending, 753,707 cm 1. See Appendix E, Table E-l for patterns in region C for substituted pyridines. 

Bellamy, L.J. (1975). The Infrared Spectra of Complex Molecules, 3rd ed. London Chapman and Hall New York Halsted-Wiley. 

Bellamy, L.J. (1968). Advances in Infrared Group Frequencies. London Methuen. 

Coleman, P.A. (1991). Practical Sampling Techniques for Infrared Analysis. Boca Raton, FL CRC Press. 

Colthup, N.B., Daly, L.H., and Wiberley, S.E. (1990). Introduction to Infrared and Raman Spectroscopy, 3rd ed. New York and London Academic Press. 

The spectra of heteroaromatic compounds result primarily from the same vibrational modes as observed for the aromatics. 

1 C—H Stretching Vibrations Heteroaromatics, such as pyridines, pyrazines, pyrroles, furans, and thiophenes, show C—H stretching bands in the 3077-3003 cm1 region. 

Ring stretching vibrations occur in the general region between 1600 and 1300 cm K The absorption involves stretching and contraction of all of the bonds in the ring and interaction between these stretching modes. The band pattern and the relative intensities depend on the substitution pattern and the nature of the substituents. 

Pyridine (Fig. 3.35) shows four bands in this region and, in this respect, closely resembles a monosubstituted benzene. Furans, pyrroles, and thiophenes display two to four bands in this region. 

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The product has the following spectral properties infrared (KBr) cm.-1 3103 and 3006 (aromatic C—H), 2955, 2925, and 2830 (aliphatic C—H stretching), 1257 and 1032 (aromatic methyl ether), 841 and 812 (C—H out-of-plane bending of isoxazole C4—H and 4-substituted phenyl) proton magnetic resonance (trifluoroaeetic acid) 5, multiplicity, number of protons, assignment 3.98 (singlet,... 

Assignments for C—H out-of-plane bending bands in the spectra of substituted benzenes appear in the chart of characteristic group absorptions (Appendix C). These assignments are usually reliable for alkyl-substituted benzenes, but caution must be observed in the interpretation of spectra when polar groups are attached directly to the ring, for example, in nitroben-zenes, aromatic acids, and esters or amides of aromatic acids. 

The insoluble material is assumed to be the graft copolymer and this is verified by infrared spectroscopy. For grafting onto the butadiene portion of a copolymer, the C-H out-of-plane bending vibrations as well as the olefin C-H stretching vibration are most useful. The graft copolymer of acrylonitrile onto polystyrene cannot be analyzed by infrared spectroscopy since the only change would be in the C-H overtone region and these bands are too weak to permit interpretation. 

Jonas and co-workers (68) used Raman spectroscopy to study the naphthalene-C02 system under high pressure. The experimental results (a blue shift of the C-H stretching and C-H out-of-plane bending modes) and model calculations presented indicate that quadrupole-quadrupole coupling is significant in this system. The preferred orientation of the 0=C=0 and naphthalene were determined to be face-to-face. 

Aromatic C-H out-of-plane bend for non-adjacent, peripheral H atoms... 

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