Nuclear magnetic resonance chemical shifts for alcoholic and phenolic protons in dimethyl sulphoxide: utility as a structural parameter

Abstract

The n.m.r. spectra of various pyridyl alcohols and phenols were measured in dimethyl or [²H₆]dimethyl sulphoxide. Pyridyl alcohols were classified into three categories on the basis of their n.m.r. behaviour. In cases in which the hydroxy-proton was sufficiently fixed in space through intermolecular hydrogen bonding with the solvent, the n.m.r. signal was a triplet due to coupling with the α-methylene group. The δ_OH value was found to be temperature dependent and to vary with change of the structural nature of hydroxy-group. Various types of intra- and intermolecular hydrogen bonding interactions are invoked for the elucidation of n.m.r. patterns. Several N-methylated pyridyl alcohols were subjected to n.m.r. investigation, but failed to provide well resolved n.m.r. patterns. The correlation between δ_OH and pK_HA of the corresponding phosphates proved the reliability of δ_OH as a structural parameter for a linear free energy relationship study of phosphate hydrolysis.