Photoreaction of 2-chlorothiophenol studied by low-temperature matrix-isolation IR spectroscopy with DFT calculation

The photoreactions of 2-chlorothiophenol are investigated using matrix-isolation IR spectroscopy combined with density functional theory calculation at the B3LYP/6-311++G(3df,3pd) level. In a Ne matrix, 2,4-cyclopentadien-1-ylidenemethanethione, a five-membered-ring thioketene compound, is identified as the major photoproduct of a reaction similar to Wolff rearrangement. The reaction intermediate is spectroscopically detected as benzothiirene, which is produced from the reactant under UV (lambda >= 275 nm) irradiation and is then converted to the thioketene under lambda >= 325 nm irradiation. Moreover, the complex of benzothiirene and HCl changes into 4-chloro-2,5-cyclohexadiene-l-thione under irradiation at lambda >= 325 nm. By contrast, UV irradiation of 2-chlorothiophenol in an Ar matrix yields primarily 4-chloro-2,5-cyclohexadiene-1-thione via its isomer 2-chloro-2,4-cyclohexadiene-1-thione. (C) 2021 Elsevier B.V. All rights reserved.