Non-adiabatic coupling constants for the disrotatory and conrotatory isomerization paths between butadiene and cyclobutene

The S₁S₀ non-adiabtic coupling constants were calculated for the disrotatory and conrotatory paths of the isomerization reaction between butadiene and cyclobutene. The calculated non-adiabatic coupling terms showed clearly the difference between the non-adiabatic interactions of the two reaction processes, and they correlate well with the Woodward-Hoffman rule.