High-Pressure Photochemistry of Alkenes. 4. The 184.9-nm Photolysis of Cyclopentene

Article abstract of DOI:10.1021/j100287a043

A systematic study of the 184.9-nm photolysis of cyclopenetene was made in the presence of added propane between 1 Torr and 6 atm.The main products are isomers at pressures higher than 100 Torr.Among them, linear 1,3- and 1,4-pentadienes as well as cyclic vinylcyclopropane and methylenecyclobutane are observed with tiny amounts of isoprene and 1-pentyne.It appears that methylenecyclobutane is the only primary product involving the Rydberg excited state.At a lower pressure, fragmentation products are also observed.They are mainly cyclopentadiene, ethylene, vinyl and allyl radicals, allene, acetylene, and propylene.Hydrogen atoms are also formed with relatively high quantum yields.Acetylene and propylene are probably formed from the same precursor.The formation of ethylene and allene is probably linked to the fragmentation of electronically excited methylenecyclobutane, and its lifetime has been estimated to be ca. 10 ps.