High pressure photochemistry of alkenes. 6. the caee of 1-methylcyclopentene at 184.9 and 147.0 nm

The degradaiion of the 184.9 nm photoexcited 1-methyl-1-cyclopentene molecule shows the involvement of various excited isomers. The most important fragmentation products are 1- and 2-methyl-1,3-cyclopentadiene. These products are probably the result of a one-step elimination process of a hydrogen molecule. This process has also been observed in the case of the 184.9 nm photochemistry of cyclopenten. On the other hand, the involvement of isomers, although possible, is not so obvious at 147.0 nm. Moreover, in this case, the 1- and 2-methyl-1,3-cyclopentadiene formation is the result of hydrogen atom elimination in a two-step process. Cyclopentadiene, ethylene, and various C₃ and C₄ compounds are formed as well as methyl radicals and hydrogen atoms. These products are probably formed in successive elimination reactions as this is also observed in acyclic alkenes.