Fragmentation and isomerization of 1,2-dimethylcyclobutane

The potential surface of 1,2-dimethylcyclobutane is investigated with respect to fragmentation and isomerization by the semiempirical MO method SINDO1. Energy and geometry of eight transition states and four intermediates are determined for the nonconcerted fragmentations under optimization of all internal coordinates. We find that symmetric cleavage ofcis-dimethylcyclobutane is the most favored process leading to fragmentation. Whereas the symmetric elimination involves two different barrier heights, the asymmetric elimination involves only two equal barrier heights. The possibility of isomerization ofcis- totrans- dimethylcyclobutane was also studied and revealed two different barrier heights lower than the corresponding heights for fragmentation.