Methyl group librations in sterically hindered dimethylnaphthalene molecules: neutron diffraction studies of 1,8-dimethylnaphthalene between 50 and 200 K

Abstract

The structure of 1,8-dimethylnaphthalene has been studied by variable temperature single crystal neutron diffraction. The location of the two methyl groups on the same side of the naphthalene ring leads to substantial steric effects, notably a hindering of the methyl group librations. This steric effect appears to dominate over the alternative possibility of coupled motions of these groups. The results are compared directly with those from the related compound 1,5-dimethylnaphthalene where there is no possibility of methyl group coupled motions, but also less severe steric hindrance.