Effect of sp2 and sp hybridised atoms on barriers to rotation in highly substituted ethanes. Steric acceleration of conformational processes

Barriers to rotation about the central bond of the 1,2,2-trimethylbutyl (triptyl) group, i.e. barriers to rotation of the t-butyl group, are reported for a series of triptyl compounds But–C(CH3)2X, where the atom in X bonded to the triptyl group is an sp2 or sp hybridised carbon. Barriers in some similar compounds are also reported. Results are discussed in terms of the interactions arising during rotation, and of steric acceleration of conformational processes.