High vibrational overtone photochemistry of 1-cyclopropylcyclobutene

Abstract

Laser excitation of high CH stretching overtones has been used to induce the isomerization of 1-cyclo-propylcyclobutene (CYCB) to 2-cyclopropyl-1,3-butadiene. Values of the unimolecular isomerization rate constant, k(E), have been measured for excitation of the fifth cyclobutenyl and cyclopropyl methylenic CH stretching overtones. The values of k(E) depend only on total energy and do not show any identifiable dependence on which type of CH overtone is excited. In particular, excitation of the cyclobutenyl methylenic CH overtone transition does not lead to any observable enhancement in k(E) relative to excitation of the cyclopropyl methylenic CH overtone transition. The value of k(E) for excitation of the cyclobutenyl methylenic CH overtone transition does not increase even when 99.8% of the excited molecules are collisionally deactivated prior to reaction. This leads to the conclusion that any vibrational energy which is introduced into the cyclobutenyl ring by overtone excitation is randomized over both the cyclobutenyl and cyclopropyl rings prior to reaction. © 1983 American Chemical Society.