title: Bond strengths: the importance of hyperconjugation.
abstract: [Structure: see text] Gronert (J. Org. Chem. 2006, 71, 1209) has challenged the importance of hyperconjugation in determining C-H bond dissociation enthalpies (BDEs) in alkanes. Electron paramaganetic resonance spectra of H3CCH2*, (H3C)2CH*, and (H3C)3C* show significant positive spin on their beta-H3C groups' hydrogens. A 55%/45% partitioning of these spins between hyperconjugation and spin polarization mechanisms linearly correlates with the C-H BDEs in methane, ethane, propane, isobutane and propene. Hyperconjugation is an important factor determining alkane C-H BDEs.
authors.affiliation: National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, Canada K1A 0R6. keith.ingold@nrc.ca
authors.forename: K U
authors.initials: KU
authors.lastname: Ingold
authors.forename: Gino A
authors.initials: GA
authors.lastname: DiLabio