Absorption Spectra and Photochemical Rearrangements of 1-, 2-, and 3-Chlorocycloheptatriene, 7-Chloronorbornadiene, and Benzyl Chloride Cations in Solid Argon

Article abstract of DOI:10.1021/j100216a006

Matrix photoionization of chlorocycloheptatriene (CCHT) during condensation with excess argon at 20 K produced new broad 484-, 517-, and 544-nm bands, a sharp 469.3-nm absorption, and weak 453- and 468-nm bands.The broad bands are assigned to the 1-, 2-, and 3-chlorocycloheptatriene cations.Photolysis with 500- 1000-nm radiation decreased the broad bands and increased the sharp 469.3-nm absorption.The 469.3-nm band and a sharp 707.8-nm counterpart in benzyl chloride experiments suggest a conjugated triene cation identification with 6-chloro-5-methylene-1,3-cyclohexadiene cation (3) as the most reasonable possibility.The 453- and 468-nm bands, which markedly increased on near-UV photolysis in benzyl chloride experiments, were strong products in similar studies with 7-chloronorbornadiene.Photolysis with 470-1000-nm radiation decreased the 468-nm band and increased the 453-nm absorption; this interconversion was reversed with 370-460-nm radiation.The latter bands are probably due to E and Z isomers of 5-(chloromethylene)-1,3-cyclohexadiene cation (6), which isomerize upon photoexcitation.