Photoreaction mechanisms of 2-chlorophenol and its multiple chloro-substituted derivatives studied by low-temperature matrix-isolation infrared spectroscopy and density-functional-theory calculations

Photoreaction mechanisms of 2-chlorophenol, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,6-dichlorophenol and 2,4,5-trichlorophenol in low-temperature argon matrices are investigated by Fourier transform infrared spectroscopy. The observed infrared bands of photoproducts are assigned with an aid of density-functional-theory (DFT) calculations, where the 6-31++G** basis set is used to optimize geometrical structures. It is concluded that five-member-ring ketene, cyclopentadienylidenemethanone (CPYM), is produced through keto carbene, 2-oxocyclohexa-3,5-dienylidene, by dissociation of hydrogen chloride. The geometries of HCl-CPYM complexes in a matrix cage are derived from the vibrational shifts of the hydrogen chloride. (C) 2001 Elsevier Science B.V. All rights reserved.