Ab initio studies of (1,2)-hydrogen migrations in open-shell hydrocarbons: vinyl radical, ethyl radical, and triplet methylcarbene

Abstract

Ab initio, POL-CI calculations on the barriers to hydrogen migration in the title compounds are reported. For C/sub 2/H/sub 3/, C/sub 2/H/sub 5/, and CH/sub 3/CH the predicted barriers are 57, 46, and 53 kcal/mol, respectively. For the first two molecules barriers to C-H bond cleavage are also calculated and found to be lower than the migration barriers. A qualitative analysis of the wave functions indicates that the high migration barriers are due to a geometrical constraint placed on the electronic structure of the transition state. A comparison to hydrogen migration in a closed-shell molecule (vinylidene-acetylene) is also presented.