Electronic spectra of organic molecules and their interpretation—IX

Abstract

Abstract The effect of substituents X  OH, NH2, NH3+, Ph, CN, Cl, Br, and I in the o-, m- and p-isomers of MeOC6H4CH2X on the K and B bands have been measured and interpreted qualitatively in terms of the hypotheses of terminal and side chain group effects. For the K bands the electron migration accompanying light absorption is along the long axis of molecule so that substituents orientated para to each other are terminal groups and can have a large effect on the K band whereas ortho and meta substituents are in the side chain and, in the absence of steric effects, have a relatively minor effect. For B bands the electron migration is perpendicular to that involved in the K band and consequently ortho substituents are terminal groups and strongly influence the intensity and wave-length of the B band while para groups have a small effect. For m-isomers the behaviour is intermediate between the o- and p-isomers but is more closely similar to the behaviour of the corresponding o-isomer than to the p-isomer. The effect of the CH2Br and CH2I groups is shown to be, for both K and B bands, very similar to the effects of groups such as carbonyl or vinyl group, which are capable of π-π interaction with the benzene ring.