Abstract: The nature of the interaction between methyl and a trigonal carbon has been examined by the effect of substituents on the methyl rotational barrier. Barriers have been measured for para-substituted toluenes and for cis-and trans-substituted propenes by the motional effects of methyl rotation on dipole-dipole spin-lattice relaxation. The toluene barriers exhibit a fair correlation with u1 and a very poor one with uR. Thus ...
