NBO-based CI/MP through-space/bond interaction analysis and its application to stereoelectronic effects in S_N2 reactions

NBO-based CI/MP through-space/bond interaction analysis was developed to analyze specific orbital interactions under consideration of the effects of electron correlation. This treatment was applied to the analysis of stereoelectronic effects in S_N2 reactions of allyl bromide in which the effects of electron correlation play an important role (ammonia was used as the nucleophilic reagent). The S_N2 activation energy in allyl bromide is lower than that in propyl bromide, because both the σ-π* and π-σ* interactions in allyl bromide contribute equally to the stabilization of the transition state.