C-13-NMR relaxation study of the methyl group rotation in 2-methyl-quinoline

A C-13-NMR relaxation time T-1 study of the methyl group rotation has been carried out from 27 degrees C to 111 degrees C in the liquid state. The C-13 relaxation time T-1 of the methyl carbon varies from 4.1 a (at 27 degrees C) to 12.889 s (at 111 degrees C). The relaxation time TI has been separated into dipole-dipole relaxation time T-1(DD) with the help of nuclear Overhauser enhancement factor eta. The eta values indicate that the relaxation mechanism is mostly dipolar in nature. The graph of In T-1(DD) versus 1000/T [K-1] is linear and the activation energy associated with the methyl group rotation obtained from slope is 3.49 +/- 0.16 kcal/mol with a regression coefficient r = 0.994. This energy agrees with the value of 3.04 +/- 0.17 kcal/mol obtained previously from a proton relaxation study.

S T H SHERAZI ,A W K KHANZADA ,M H PHULPHOTO ,