Relaxation processes in aromatic methyl groups. I 2-Chloro- and 2, 6-Dichloro-toluene

Abstract

Three series of selectively deuterated toluenes, 2-chlorotoluenes and 2,6-dichlorotoluenes have been synthesized, and their methyl group 1H n.m.r. relaxation pathways have been determined by 1H, 2H and 13C n.m.r. spin-lattice relaxation time measurements. 1H spin-lattice relaxation in the methyl groups of these series occurs predominantly through an intramethyl H-H dipolar mechanism as well as through the spin-rotation mechanism. Dipolar spin-lattice relaxation rates for intramethyl H-H pairs are 0.012, 0.020 and 0.025 s-1 for toluene, 2,6-dichlorotoluene and 2-chlorotoluene respectively, suggesting a decrease in the rate of methyl group rotation in this order. Ab initio molecular orbi..