Matrix Photochemistry of CH3C(O)SX Molecules with X = H, CH3, and C(O)CH3: Formation of Ketene in Another Decomposition Channel of Sulfenyl Carbonyl Compounds

Abstract

CH 3 C(O)SC(O)CH 3 isolated in solid Ar, N 2 , or 5% CO-doped Ar at 15 K and CH 3 C(O)SH and CH 3 C(O)-SCH 3 isolated in solid Ar at 15 K were irradiated with broad-band UV-visible light (200 ≤ λ ≤ 800 nm). On the basis of the IR spectra of the matrixes, hydrogen abstraction from the CH 3 group to give ketene, H 2 C=C=O, with the elimination of HX [X = SC(O)CH 3 , SH, or SCH 3 ] was identified in each case as the main channel of photodecomposition within the confines of a solid matrix environment. The presence of a CH 3 ligand attached to the carbonyl function thus introduces a third type of elimination reaction for matrix-isolated sulfenyl carbonyl compounds of the general type XC(O)SY. Additionally, the conformational properties of the CH 3 C(O)SX molecules have been investigated. In the case of thioacetic acid (X = H), the matrix experiments indicate that the vapor at ambient temperatures consists of a mixture of the syn and anti forms, with the syn form predominating (ca. 85%). Broad-band UV-visible irradiation then results in interconversion of the conformers prior to decomposition. The identification of the different molecules has been underpinned by the results of ab initio and density functional theory (DFT) calculations.