Kinetics of the Reversible β-Scission of the Cyclopentyloxy Radical

Article abstract of DOI:10.1021/ja00183a035

The reaction of N-(cyclopentyloxy)pyridine-2-thione (6) with tributylstannane in benzene constitutes a clean experimental system for a kinetic study of the β-scission of the cyclopentyloxy radical (1).Product distributions are reported as a function of tributylstannane concentration over a temperature range of 6-80 deg C.The results are consistent with a mechanism involving a reversible β-scission.Arrhenius parameters for the β-scission of the cyclopentyloxy radical (1) are log A (s^-1)=12.55+/-0.41 and E_a=6.26+/-0.54 kcal/mol, while those for the reverse reaction, the 1,5-exo cyclization of the 4-formylbutyl radical (2), are log A (s^-1)=10.2+/-0.3 and E_a=6.88+/-0.46 kcal/mol.The observed equilibrium constants and activation parameters are compared with theoretical calculations including group-additivity equilibrium constants and AM1-UHF activation parameters.