Diffusion controlled hydrogen atom abstraction from tertiary amines by the benzyloxyl radical. The importance of C-H/N hydrogen bonding

The rate constants for H-atom abstraction (k(H)) from 1,4-cyclohexadiene (CHD), triethylamine (TEA), triisobutylamine (TIBA), and DABCO by the cumyloxyl (CumO(?)) and benzyloxyl (BnO(?)) radicals were measured. Comparable k(H) values for the two radicals were obtained in their reactions with CHD and TIBA whereas large increases in k(H) for TEA and DABCO were found on going from CumO(?) to BnO(?). These differences are attributed to the rate-determining formation of BnO(?) C-H/amine N lone-pair H-bonded complexes.