Em. Goldfield, Quantum dynamics of the trimethylene biradical - Stereomutation of cyclopropane and unimolecular decay, FARADAY DIS, (110), 1998, pp. 185-205
A reduced-dimensionality three degrees-of-freedom quantum dynamics calculat
ion of the stereomutation of cyclopropane has been performed. In one set of
calculations, wavepackets are initiated centered around stationary points
on the conrotatory, disrotatory and single rotation (cis/trans conversion)
pathways. The ratio of trans to cis isomer formed, R-tc, is shown to be hig
hly dependent on the location, and average energy of the initial wavepacket
as well as the initial orientation of the terminal methylene torsions. In
a second set of calculations, wavepackets are initiated as 'highly excited
cyclopropane', in one of the four possible isomeric configurations, designa
ted as a tl ans configuration for the purposes of analysis. Here also, R-tc
depends on the initial torsional orientation. Analysis of wavepacket densi
ty and the time constants for formation of product density indicate that th
at the contributing mechanisms range from direct, concerted conrotatory mot
ion to more statistical behavior. A 'Boltzmann' average at 695 K of the rat
io of 'double' to 'single' rotations, k(12)/k(1), results in k(12)/k(1) = 2
R(tc) = 2.2. Wavepacket density is shown to orient preferentially along the
conrotatory and disrotatory pathways rather than the higher energy single
rotation(cis/trans conversion) pathway.