Study of molecular motion in t-butyl halides by pulsed proton magnetic resonance

Abstract

The proton spin–lattice relaxation times of t-butyl chloride, bromide and iodide were measured at 60 MHz over the temperature interval 330-100 K. In this interval three solid phases have been observed for t-butyl chloride and bromide but only two solid phases for the iodide. The temperature dependence of T₁ demonstrates that three types of molecular motion, translational, molecular tumbling and methyl group reorientation, occur in turn over the temperature interval. Activation energies for the methyl group reorientations were 10.8, 9.0 and 9.6 kJ mol^–1, respectively, for t-butyl chloride, bromide and iodide. The experimental minima in T₁ at low temperatures are in agreement with theoretical expectation for these three compounds.