Alternation in spin-lattice relaxation times and barrier height to methyl reorientation in sodium and lithium soaps

Abstract

The influence of methyl group reorientation on the spin-lattice relaxation of protons in odd- and even-numbered sodium and lithium soaps and in some binary mixtures of sodium soaps has been investigated. Spin-lattice relaxation measurements show that the methyl group packing in the odd-numbered soaps is denser than in the even-numbered ones, which is in agreement with results obtained by dilatometric investigations. The contribution of intermolecular interactions to the spinlattice relaxation time is greater in the odd-numbered soaps than in the even-numbered ones, which is reflected in a higher energy barrier to the methyl group reorientation in the odd-numbered soaps. Interactions of methyl groups with methylene groups in mixtures of sodium soaps heighten the barrier to the methyl group reorientation; this effect increases as the difference in chain length between the components of the mixture becomes greater.