Solid state proton spin relaxation and t-butyl and methyl group reorientation in 1-bromo-2,4,6-tri-t-butylbenzene

We have used the solid state proton spin relaxation technique to investigate the barriers for methyl and t‐butyl group reorientation in polycrystalline 1‐bromo‐2,4,6‐tri‐t‐butylbenzene. The barriers in the range of 15–19 kJ/mol (3–5 kcal/mol) are compared with those found in related molecules. It is shown that the neighboring ring bromine atom has an effect on the barrier for t‐butyl group reorientation similar to that of a neighboring hydrogen atom despite the significantly larger van der Waals’ radius of a bromine atom. This most likely occurs because of the relatively long carbon–bromine bond, the distorted ring geometry, and the relatively high polarizability of bromine. In addition, the barriers for methyl group reorientation, about 16 kJ/mol, seem to be largely intra‐t‐butyl in origin.