Direct Measurements of the Absolute Rates of Dimerization and Capture of the 2-Isopropylidenecyclopenta-1,3-diyl Species by Electron Paramagnetic Resonance Spectroscopy

Article abstract of DOI:10.1021/ja00527a038

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.