17O and 2H quadrupole double resonance in some acid carboxylates

Abstract

An ¹⁷O and ²H quadrupole double resonance study has been made of a number of strong O—H—O hydrogen bonds in acid carboxylates and related compounds and an analysis of the ¹⁷O ¹H dipolar structure in one (potassium hydrogen maleate). The compounds selected show a range of hydrogen-bond structures varying from symmetric and centred to asymmetric and non-centred; with certain assumptions, it is possible to follow the consequent changes in sign and orientation of the ¹⁷O quadrupole coupling tensor. The arguments are based on the proposal that the ¹⁷O quadrupole coupling constant is negative in symmetric hydrogen bonds, its orientation being related to that of the ¹⁷O tensor in the C—¹⁷OH group in carboxylic acids by a rotation of 25 ° with respect to the O—H direction. The behaviour of the ²H quadrupole coupling constant and asymmetry parameter in strong O—H—O hydrogen bonds is discussed in terms of the position of the hydrogen atom.