The Magnitude of Hyperconjugation in Ethane: A Perspective from Ab Initio Valence Bond Theory

Abstract

Steric effect dominates: Ab initio valence bond and block-localized wavefunction methods are used to estimate the contributions of hyperconjugation and steric effects to the ethane rotation barrier. The results show that hyperconjugation stabilizes the staggered conformer by about 4 kJ mol−1 relative to the eclipsed form (see picture) and steric hindrance is the major driving force behind the favoring of the staggered conformation in ethane.