Tunnelling Corrections in Hydrogen Abstractions by Excited-State Ketones

Monica Barroso (1, 2) , Luis G Arnaut (3) , Sebastiao J Formosinho (3)

1 Department of Chemistry [Imperial College London]
2 Chemistry Department
3 Chemistry Department

Hydrogen abstraction from 1-phenylethanol by triplet acetophenone occurs from both C-H and O-H bonds. The reaction path of the Interacting-State Model (ISM) is used with the Transition-State Theory (TST) and the semiclassical correction for tunnelling (ISM/scTST) to help rationalizing the experimental kinetic results and elucidate the mechanisms of these reactions. The weak exothermicity of the abstraction from the strong O-H bond is compensated by electronic effects, hydrogen bonding and tunnelling, and is competitive with the more exothermic abstraction from the α-C-H bond of 1-phenylethanol. The alkoxy radical formed upon abstraction from O-H reacts within the solvent cage and the primary product of this reaction is 1-phenylethenol. The corresponding kinetic isotope effect is ca. 3 and is entirely consistent with a tunnelling correction ca. 9 for H abstraction. We therefore demonstrate that the tunnelling correction is the major contributor to the kinetic isotope effect.

Mots clés: Physical Sciences

Monica Barroso, Luis G Arnaut, Sebastiao J Formosinho. Tunnelling Corrections in Hydrogen Abstractions by Excited-State Ketones. Journal of Physical Organic Chemistry, 2010, 23 (7), pp.702. ⟨10.1002/poc.1708⟩. ⟨hal-00552420⟩