REAPPRAISAL OF THE DISROTATORY TRANSITION-STATE FOR THE RING-OPENING OF CYCLOPROPANE

New ab initio studies using double zeta plus polarization (DZP) and triple zeta plus double polarization (TZ2P) basis sets, analytic derivative methods, and single- or two-configuration self-consistent-field (SCF) wavefunctions have provided energies, geometries, dipole moments, and harmonic vibrational frequencies for cyclopropane and for three conformationally isomeric singlet trimethylene diradical species. Furthermore, configuration interaction with single and double excitations (CISD) energies for these four C3H6 stationary points were determined at the SCF optimized geometries. The previously neglected disrotatory transition state has been found and characterized. The energetic ordering and spacing of the trimethylene diradical stationary point structures deviate significantly from earlier estimations, and suggest a new mechanistic possibility for thermal geometrical isomerizations of isotopically substituted cyclopropanes.