Journal article
Bond dissociation energies and radical stabilization energies associated with substituted methyl radicals
The Journal of Physical Chemistry A, Vol.105(27), pp.6750-6756
2001
Abstract
Bond dissociation energies (BDEs) and radical stabilization energies (RSEs) associated with a series of 22 monosubstituted methyl radicals (•CH2X) have been determined at a variety of levels including, CBS-RAD, G3(MP2)-RAD, RMP2, UB3-LYP and RB3-LYP. In addition, W1′ values were obtained for a subset of 13 of the radicals. The W1′ BDEs and RSEs are generally close to experimental values and lead to the suggestion that a small number of the experimental estimates warrant reexamination. Of the other methods, CBS-RAD and G3(MP2)-RAD produce good BDEs. A cancellation of errors leads to reasonable RSEs being produced from all the methods examined. CBS-RAD, W1′ and G3(MP2)-RAD perform best, while UB3-LYP performs worst. The substituents (X) examined include lone-pair-donors (X = NH2, OH, OCH3, F, PH2, SH, Cl, Br and OCOCH3), π-acceptors (X = BH2, CH=CH2, C≡CH, C6H5, CHO, COOH, COOCH3, CN and NO2) and hyperconjugating groups (CH3, CH2CH3, CF3 and CF2CF3). All substituents other than CF3 and CF2CF3 result in radical stabilization, with the vinyl (CH=CH2), ethynyl (C≡CH) and phenyl (C6H5) groups predicted to give the largest stabilizations of the π-acceptor substituents examined and the NH2 group calculated to provide the greatest stabilization of the lone-pair-donor groups. The substituents investigated in this work stabilize methyl radical centers in three general ways that delocalize the odd electron: π-acceptor groups (unsaturated substituents) delocalize the unpaired electron into the π-system of the substituent, lone-pair-donor groups (heteroatomic substituents) bring about stabilization through a three-electron interaction between a lone pair on the substituent and the unpaired electron at the radical center, while alkyl groups stabilize radicals via a hyperconjugative mechanism. Polyfluoroalkyl substituents are predicted to slightly destabilize a methyl radical center by inductively withdrawing electron density from the electron-deficient radical center.
Details
- Title
- Bond dissociation energies and radical stabilization energies associated with substituted methyl radicals
- Authors/Creators
- D.J. Henry (Author/Creator) - Australian National UniversityC.J. Parkinson (Author/Creator) - Australian National UniversityP.M. Mayer (Author/Creator) - Australian National UniversityL. Radom (Author/Creator) - Australian National University
- Publication Details
- The Journal of Physical Chemistry A, Vol.105(27), pp.6750-6756
- Publisher
- American Chemical Society
- Identifiers
- 991005543808907891
- Copyright
- © 2001 American Chemical Society
- Murdoch Affiliation
- Murdoch University
- Language
- English
- Resource Type
- Journal article
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- Citation topics
- 2 Chemistry
- 2.15 Physical Chemistry
- 2.15.3 Quantum Chemistry
- Web Of Science research areas
- Chemistry, Physical
- Physics, Atomic, Molecular & Chemical
- ESI research areas
- Chemistry