The—ON Stretching Vibration

General. Infra-red absorption from nitriles is to be expected in the triple-bond region 2300—2000 cm . Early studies on isolated molecules confirmed that this was sO [1—8] and the correlation was put on a firm foundation by Kitson and Griffiths [9] who studied the spectra of some seventy nitriles. These workers found that in thirty-four saturated mono- and di-nitriles (excluding malononitrile) the ON frequency lies between 2260 cm and 2240 cm , and in a further seventeen unsaturated but not conjugated nitriles the 

Open-chain compounds Open-chain o/J-unsaturated compounds Conjugated cyclic compounds 

These findings have been fully substantiated by later workers [10, 14, 16, 20, 22, 37, 38, 82], and some refinements of the correlations have been developed. Thus, in aromatic nitriles [10, 16] the overall frequency shifts with changes in the substituents are very small, ranging from 2222 cm for a-naphthyl nitrile to 2240 cm for meta-nitro benzonitrile, but the shifts do reflect the Hammett a values of the substituents so that the frequency can be predicted with reasonable confidence if these are 

With alkyl nitriles the overall range is so small as to make any differentiation difficult. However there is a regular frequency fall as one passes along the series from acetonitrile (2247 cm ) to /er/-butyl nitrile (2236 cm ), indicating a slight frequency fall for each successive substitution at the a-carbon atom. Halogens substituted at this point have a different effect. The first chlorine raises the frequency by 11 cm but further substitution reduces the frequency to nearer the original value. 

Mocyanide [39] absorbs at 2166 cm . They also observed a new band near 1592 cm in the spectra of the wo-nitriles which is absent from those of the nitriles. There is, however, no band in this region in methyl wo-cyanide which has been studied by Williams [39]. 

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