Proton magnetic resonance and relaxation in solid tertiary butyl amine-tropolone adduct

Abstract

Proton magnetic resonance absorption and spin-lattice relaxation time measurements have been carried out for solid tertiary butyl amine-tropolone adduct, (CH 3) 3-CNH 3 +Tr −, in the temperature range of 66–425 K. The absorption line measurements show that the structure is rigid on the NMR timescale at the lowest temperatures studied, while at higher temperature the motional behavior ranges from rotation of the methyl groups to additional composite motion involving reorientations of both the tertiary butyl group and the NH 3 + about the CN bond. The proton spin-lattice relaxation time measurements exhibit two minima, one (41.4 msec) centered at 208 K due to the methyl group motion, and another (50.5 msec) centered at 380 K due to the composite motion of tertiary butyl and NH 3 + reorientations. By fitting the relaxation time measurements for the adduct and its partially deuterated (−ND 3 +) analog to appropriate relaxation rate expressions, activational energy barriers of 2.99±0.28, 10.5±1.5, and 7.23±0.6 kcal mole −1 are obtained for the methyl group motion, tertiary butyl group motion, and the NH 3 + group motion, respectively.