80939-31-7Relevant academic research and scientific papers
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 (1980)
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.
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 (1982)
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.
A Ranking of Diylophilic Reactivities of Olefins toward the Singlet and Triplet Forms of the Trimethylenemethane Biradical, 2-Isopropylidenecyclopenta-1,3-diyl
Duncan, Charles D.,Corwin, Leonard R.,Davis, James H.,Berson, Jerome A.
, p. 2350 - 2358 (2007/10/02)
The relative rates of cycloaddition of olefins with the trimethylenemethane (TMM) derivative 2-isopropylidenecyclopenta-1,3-diyl (1) can be determined by direct competition experiments.The gross relative activities in turn can be dissected into singlet and triplet relative reactivities by two techniques.The first involves the determination of the competition ratio for entrapment of the singlet TMM by a given olefin vs. intersystem crossing (isc) to the triplet, combined with the assumption that the rate of isc is independent of the olefin.The second uses the concentration of a "marker" product from the limiting singlet product distribution (obtained from oxygen-saturated runs) and the limiting spin-equilibrated (mostly triplet) product distribution as a guide to the fraction of singlet-derived and triplet-derived products from a given olefin under the conditions of competition.The relative reactivities toward the singlet follow: maleic anhydride, 235; maleonitrile, 180; fumaronitrile, 160; dimethyl fumarate, 67; acrylonitrile, 4.5; methyl acrylate, 0.9; dimethyl maleate, 1.0.The relative triplet reactivities for the last four olefins are respectively 59, 35, 12, and (1.0).The results are consistent with the idea of a concerted cycloaddition of the singlet and a nonconcerted one of the triplet.
