AN INFRARED STUDY OF SUBSTITUTION IN THE BENZENE RING

Limited but representative series of phenol and benzonitrile derivatives (ortho, meta and para) were assembled and the OH and C N band frequencies and intensities were determined. The method of "segments" was used to evaluate the latter. Substituents are shown to divide themselves into three classes on the basis of their effect on the electronic distribution of the unperturbed ground state of the molecules, and these classes are the same as those obtained on the basis of chemical reactivity. There is, however, no complete analogy between the phenol and the benzonitrile derivatives. The observed frequencies and intensities are related to electronic distribution, and it is shown that the existence of the three groups is entirely compatible with a smooth variation of the electronic charges sent by the substituent into (ortho), meta and para in the series NH2, OH, F, Cl, Br, I, CHO, C N, NO2.