Photochemical rearrangement reactions of 2-n-propylcyclopentanone

Abstract

Photolysis of 2-n-propylcyclopentanone in the vapor phase at about 140° with 3130-Å. radiation gave rise to carbon monoxide, ethylene, propylene, 1-pentene, a C7 hydrocarbon, cyclopentanone, and trans-4-octenal. The production of carbon monoxide, along with C2, C5, and C7 hydrocarbons, and the formation of trans-4-octenal represent well-known primary processes in cyclic ketones. However, the formation of cyclopentanone and propylene in equivalent amounts represents the first observation of the Norrish type II process in an alicyclic ketone. The quantum yield for this process has been determined to be 0.08. The reaction was essentially unaffected by adding oxygen or by carrying it out in the liquid phase. Photolysis of 2-(n-propyl-2,2-d2)cyclopentanone showed, as in other instances, the specific nature of the hydrogen atom that underwent intramolecular transfer.