EPR data do not indicate that hyperconjugation stabilizes alkyl radicals.
Ingold and DiLabio recently proposed that a correlation between C-H bond dissociation energies (BDE's) and spin delocalization terms calculated from EPR spectra was evidence that hyperconjugation plays an important role in stabilizing alkyl radicals. This correlation cannot be extended to C-C BDE's and the nature of the deviation is inconsistent with modern data on the 1,3 carbon-carbon interaction energies in alkanes. This result suggests that hyperconjugation is not a key factor in determining BDE's.
Gronert
Scott
S
Department of Chemistry, Virginia Commonwealth University, 1001 West Main Street, Richmond, Virginia 23284, USA. sgronert@vcu.edu