CONROTATORY AND DISROTATORY PATHWAYS IN THE ELECTROCYCLIC ISOMERIZATION OF CYCLOBUTENE TO CIS-BUTADIENE - THE SPIN-COUPLED VIEWPOINT

Spin-coupled theory is used to study the changes which occur in the el ectronic wave function as a system moves along the intrinsic reaction coordinate (IRC) for the case of conrotatory and disrotatory motion in the ground-state electrocyclic interconversion of cyclobutene to cis- butadiene. It is shown that the reaction is already well under way in the conrotatory case at the transition point (considerable cis-butadie ne character), but the system still retains an overwhelming reactant ( cyclobutene) character for the disrotatory motion. In both the conrota tory and disrotatory cases, the sharp changes in the weights of the tw o spin couplings, associated with the onset of bond breaking or bond f ormation, are shown to occur at points along the IRC well after the tr ansition point. (C) 1997 American Institute of Physics.