Isotope Effects in Methyl Radical Abstraction Reactions

The high k H /k D ratio found experimentally for methyl radical abstraction reactions is explained on the basis of classical rate theory. It is shown that if the bending frequencies in the activated complex approach zero, good agreement is found between experimental and calculated k H /k D values. For abstraction of H and D from hydrocarbons, both the tunneling and classical rate theories predict acceptable k H /k D values. Abstraction of H and D from H 2 and D 2 , however, can best be explained on the basis of a classical process.