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.