Activation Parameters for Ring Opening of (Bicyclo[n.1.1]alk-1-yl)methyl Radicals

Ring opening of the (bicyclo[1.1.1]pent-1-yl)methyl (4), (bicyclo[2.1.1]hex-1-yl)methyl (5) and (bicyclo[3.1.1]hept-1-yl)methyl (6) radicals has been investigated by semiempirical molecular orbital theory MINDO/3 and AM1) and by experiment. Our results indicate that (4) ring-opens extremely rapidly, with an estimated energy barrier of less than 22 kJ mol-1. The higher homologues (5) and (6) rearrange more slowly with barriers of about 42.2 and 46.0 kJ mol-1 respectively. This trend is also observed in the MINDO/3 and AM1 results, with the latter giving the better agreement with experiment.