LIGHT-ABSORPTION STUDIES: PART X. ULTRAVIOLET SPECTRA IN ACID AND BASIC MEDIA–—SOME FURTHER OBSERVATIONS ON THE ORTHO EFFECT

Abstract

The spectra of acetophenones and related compounds are obtained in acid and basic solution and are compared with previously reported spectra of substituted benzene derivatives. Evidence is adduced that the B-bands, not only in neutral solution, but also in acid or basic solution, are determined primarily by steric and mesomeric interactions.Following previous work, the main cause of the ortho effect in the B-band of electronic spectra is ascribed to steric interactions between the vicinal substituents, and in this way, steric interactions explain the frequent similarity in the spectra of meta and ortho isomers. Other factors also play a part, and one of these, a short-range interaction between the substituent and the benzene ring, is discussed.