Carboxylic group reorientation and hydrogen bonds in Gallic acid

Abstract

Broad line PMR spectra of solid Gllic acid (3,4,5,trihydroxy benzoic acid ) were recorded in the temperature range 77and 526°K at 7.5 MHz . The lattice is found to be effectively rigid up to 340 °K . The analysis of the second moment data suggested the onset of reorientation of carboxylic group at 348 °K . The activation energy for the motions found to be 10.8 Kcal/ mole. In the temperature range 410-526 °K , p-OH group is found to exhibit remarkable motion. No change in crystalline structure was observed at or above the transition temperature.