80954-13-8Relevant articles and documents
Formal Kinetic Proof of Reversible Unimolecular Transformation to a Biradical as an Obligatory First Step in the Mechanism of Cycloaddition of 5-Isopropylidenebycyclopentane to Olefins
Mazur, Mark M.,Berson, Jerome A.
, p. 2217 - 2222 (2007/10/02)
A study of the kinetics of the cycloadditions of 5-isopropylidenebicyclopentane (2b) with acrylonitrile and maleic anhydride shows the operation of a two-step mechanism: unimolecular ring opening of the hydrocarbon to a singlet biradical (1b-S) followed by intermolecular capture of the singlet.The regiospecifity of the cycloaddition thus cannot be explained by a bimolecular hydrocarbon + olefin reaction s2? + s2? + s2?> but is most simply interpreted as an orbital simmetry effect dependent on the hierarchy of nominally NBMOs of the diyl.The kinetic data permit the assignment of a barrier of about 2.3 kcal/mol to the cyclization of the singlet biradical.
Direct Measurements of the Absolute Rates of Dimerization and Capture of the 2-Isopropylidenecyclopenta-1,3-diyl Species by Electron Paramagnetic Resonance Spectroscopy
Platz, Matthew S.,Berson, Jerome A.
, p. 2358 - 2364 (2007/10/02)
The dissapearance of the triplet electron paramagnetic resonance (EPR) signal of 2-isopropylidenecyclopenta-1,3-diyl in a propanolic medium at 143.6 K is a second-order reaction.Its rate can be measured with an accuracy of about 50percent by EPR spectroscopy and is found to be approximately 0.13 times the diffusion-controlled encounter frequency.This is too fast to permit the mechanism to be a combination of the diyl singlet with the triplet and is consistent with a triplet-triplet dimerization.The rates of cycloaddition of the triplet diyl to olefins also can be measured by EPR techniques are best interpreted as the result of a stepwise triplet plus olefin reaction, in which the two new bonds of the cycloadduct are formed sequentially rather then simultaneously.
