1H and 2H NMR relaxation study of hydrogen bond dynamics in solid naphthazarin A and C

Abstract

The proton spin-lattice relaxation times T 1 and T 2e of naphthazarin A and the deuteron spinlattice relaxation time T 1 of deuterated hydroxyl groups of naphthazarin C have been studied over a wide temperature range. The experimental results have been interpreted in terms of a relaxation model in which the proton or deuteron jumps between two potential minima in the vicinity of adjacent quinonoid and hydroxyl oxygens. The low temperature relaxation data have been interpreted in terms of a model in which quantum mechanical tunnelling dominates. The relaxation rates at higher temperatures can be explained by classical jumps across the barrier of the asymmetric potential well. 1 2e