Deuterium and Carbon-13 Kinetic Isotope Effects for the Isomerization of 5,5-Dimethylbicyclopent-2-ene to 5,5-Dimethylcyclopentadiene

Article abstract of DOI:10.1021/ja00191a032

The relative rates of electrocyclic isomerization of 5,5-dimethylbicyclo<2.1.0>pent-2-ene and the 2-(2)H, 1,2,4-(2)H3, 1,2,3,4-(2)H4, and 1,4-(13)C2 isotopic variants of this system have been determined at 43.6-44.0 deg C.There is no detectable carbon-13 effect; deuterium substitution at C(2) is associated with a small k_H/k_D effect, 1.02, and a deuterium at C(1) results in a very large effect, 1.26.The k_H/k_D(d3) effect between 24.6 and 54.7 deg C shows some sensitivity to temperature, ranging from 1.83 to 1.64.The data exclude an important magnetic isotopeeffect on the isomerization and provide no support for a singlet --> triplet intersystem crossing along the reaction coordinate.