EFFECT OF FAST INTERNAL ROTATION ON NITROGEN-14 NUCLEAR MAGNETIC RESONANCE RELAXATION TIMES OF METHYLBENZYL CYANIDES

It is shown that nmr can be used to study internal rotation which occurs at a rate comparable to the molecular rotation rate. Specifically, the nmr relaxation times of the 14N nucleus in 2-, 3-, and 4-methylbenzyl cyanide have been measured in the neat liquids and in m-xylene solutions. The relaxation times depend on both the rate of the molecular rotation and the rate of internal rotation of the CH2CN group relative to the benzene ring. At 65°, for 3- or 4-MBC in the neat liquids, the calculated diffusion constants for the molecular and internal rotation are DM = 2.1 × 1010 sec-1 and DI = 4.4 × 1010 sec-1, respectively.