What is the origin of the contrathermodynamic behavior in methyl radical addition to alkynes versus alkenes?

R. Gómez-Balderas; M.L. Coote; D.J. Henry; H. Fischer; L. Radom

doi:10.1021/jp035042z

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What is the origin of the contrathermodynamic behavior in methyl radical addition to alkynes versus alkenes?

Journal article

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What is the origin of the contrathermodynamic behavior in methyl radical addition to alkynes versus alkenes?

R. Gómez-Balderas, M.L. Coote, D.J. Henry, H. Fischer and L. Radom

The Journal of Physical Chemistry A, Vol.107(31), pp.6082-6090

2003

DOI: https://doi.org/10.1021/jp035042z

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Abstract

High-level ab initio calculations of the barriers, enthalpies, and rate constants have been performed for methyl radical addition to ethyne, propyne, ethene, and propene. We find that addition to alkenes is kinetically favored over addition to alkynes, despite the larger exothermicity of the alkyne addition reactions. The results have been rationalized using the curve-crossing model. To this end, the singlet-triplet gaps and charge-transfer energies in the reactants, and the extent of charge separation in the transition structures, have been calculated. It is concluded that the greater barrier for addition to alkynes is primarily the result of the larger singlet-triplet gap in the substrate. This barrier-raising effect dominates the barrier-lowering effect of the reaction exothermicity.

Details

Title: What is the origin of the contrathermodynamic behavior in methyl radical addition to alkynes versus alkenes?
Authors/Creators: R. Gómez-Balderas (Author/Creator) - Australian National University
M.L. Coote (Author/Creator) - Australian National University
D.J. Henry (Author/Creator) - Australian National University
H. Fischer (Author/Creator) - Australian National University
L. Radom (Author/Creator) - Australian National University
Publication Details: The Journal of Physical Chemistry A, Vol.107(31), pp.6082-6090
Publisher: American Chemical Society
Identifiers: 991005543461707891
Murdoch Affiliation: Murdoch University
Language: English
Resource Type: Journal article

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Collaboration types: Domestic collaboration; International collaboration
Citation topics: 2 Chemistry; 2.1 Synthesis; 2.1.1299 Radical Cyclization
Web Of Science research areas: Chemistry, Physical; Physics, Atomic, Molecular & Chemical
ESI research areas: Chemistry