NBO analysis of the torquoselectivity of the electrocyclic reactions of mono-substituted cyclobutenes.

Conrotatory ring opening of cyclobutene, 3-methoxycyclobutene, and 3-formylcyclobutene has been studied with the density functional theory. The stereoselectivity of these reactions has been elucidated on the basis of the natural bond orbital analysis and correlation diagrams. Hyperconjugative interactions substituent-cyclobutene occurring at the transition state seem to be responsible of these reactions' torquoselectivity. [ABSTRACT FROM AUTHOR]