Hydroxyl Frequency in Carboxylic Acids

Abstract

THE recent work of Errera and Mollet¹, Fox and Martin² and others has shown how the association of single molecules of the alcohols may be studied by means of their infra-red absorption spectra, more particularly in the region of the ‘O—H’ fundamental frequency and its overtones. In the course of an investigation (suggested by Prof. E. K. Rideal) of the inter- and intra-molecular interactions of the hydroxyl (OH) and carboxyl (COOH) groups in solutions of the ω- hydroxycarboxylic acids, we have been making a preliminary study of the infra-red absorption of some of the simpler carboxylic acids in solution and have established the existence of a similar phenomenon for association of these acids. Although indications of this have already been apparent from the work of Gillette and Daniels³ on the shift of the ‘C=O’ and ‘C—O’ frequencies during association, and from that of Badger and Bauer⁴ on a presumed overtone of the ‘O—H’ frequency in the photographic region, the effect of association on the fundamental ‘O—H’ vibration would appear to have been missed. Yet here the effect may best be studied and presents (as we have found) several interesting contrasts to the case of pure hydroxyl interaction in the alcohols.