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.