Origin of Staggered Conformational Preference in Methanol

Building on recent work on ethane internal rotation, we present a Hartree−Fock analysis that determines the origin of the conformational preference in methanol. The conformational preference origin is not inferred from barrier studies but is analyzed directly, by determining conformations the molecule would assume when particular classes of interactions are missing. We find that it is the hyperconjugative, and not the steric, interactions that determine the equilibrium structure of methanol. Rehybridization effects and bond strength changes induced by skeletal relaxations accompanying internal rotation play a critical role in the torsional mechanism.