Alkyne Substituent Effects in Radicals and Carbocations

Alkyne substituent effects in the methylenecyclopropane rearrangement as well as solvolysis studies of the structurally similar trifluoroacetates were determined. The results of these kinetic studies fell into a range that was expected. In the methylenecyclopropane rearrangement all studied systems are moderate radical stabilizers, rearranging more quickly than the parent system. Solvolytic studies showed that the sigma + values for the para-substituted trifluoroacetates are relatively similar, with the para-acetylene group the only system that showed rate retardation in reference to the parent para-hydrogen system. The studies also showed the gamma + value of the 1,2,3-triazole system is better at stabilizing a developing carbocation by a factor of 39 than a phenyl ring. This is due to further delocalization of the carbocation.