The molecular structure and conformational properties of methoxycarbonylsulfenyl chloride, CH(3)OC(O)SCl, were determinated in the gas and solid phases by gas electron diffraction, low-temperature X-ray diffraction, and vibrational spectroscopy. Furthermore, quantum chemical calculations were performed. Experimental and theoretical methods result in structures with a planar C-O-C(O)-S-Cl skeleton. The electron diffraction intensities are reproduced best with a mixture of 72(8)% syn and 28(8)% anti conformers (S-Cl bond synperiplanar/antiperiplanar with respect to C=O bond) and the O-CH(3) bond synperiplanar with respect to the C=O bond. The syn form is the preferred form and becomes the exclusive form in the crystalline solid at low temperature. This experimental result is reproduced very well by Hartree-Fock approximation and by density functional theory at different levels of theory but not by the MP2/6-311G method, which overestimates the value of DeltaG between the syn and anti conformers. The results are discussed in terms of anomeric effects and a natural bond orbital (NBO) calculation. Photolysis of matrix-isolated CH(3)OC(O)SCl with broad-band UV-visible irradiation produces an interconversion of the conformers, and the concomitant decomposition leads to formation of OCS and CO molecules.

CH 3 C(Ο)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 e λ e 800 nm). On the basis of the IR spectra of the matrixes, hydrogen abstraction from the CH 3 group to give ketene, H 2 CdCdO, 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 matrixisolated 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.

The vapor of (chlorocarbonyl)sulfenyl bromide, ClC(O)SBr, was isolated in solid Ar, Kr, N(2), and Ar doped with 5% CO at 15 K, and the matrix was subsequently irradiated with broad-band UV--visible light (200 < or = lambda < or = 800 nm), the changes being followed by reference to the IR spectrum of the matrix. The initial spectrum showed the vapor of ClC(O)SBr to consist of more than 99% of the syn form (with the C==O bond syn with respect to the S--Br bond) in equilibrium with less than 1% of the anti conformer. Irradiation caused various changes to occur. First, conformational randomization took place, leading to a roughly equimolar mixture of the two rotamers, and so affording the first spectroscopic characterization of an anti-ClC(O)S-containing compound. Simultaneously, the novel constitutional isomer syn-BrC(O)SCl was also formed. Continued photolysis resulted in the decay of all these species while revealing a third reaction channel, leading to the elimination of CO and the formation of the new triatomic sulfur halide BrSCl. The assignment of the IR bands to the different products was made on the basis of the usual criteria, taking account (i) of the effects of the naturally occurring isotopic pairs (35)Cl/(37)Cl and (79)Br/(81)Br, (ii) of the vibrational properties of related molecules, and (iii) of the properties predicted for the relevant molecules by quantum chemical calculations.

The photochemistries of the molecules ClC(O)SCl and ClC(O)SCH 3 (in both their normal and perdeuterated forms) isolated in solid Ar or N 2 matrixes at 15 K have been investigated. On the basis of evidence of the IR spectra of the matrixes, the products of irradiation with broad-band UV-visible light (200 e λ e 800 nm) were identified, thereby revealing quite different photochemical behaviors for the two molecules. ClC(O)SCl is subject to multichannel changes that include interconversion of the syn and anti rotamers, photodecomposition to give CO and SCl 2 , formation of the hitherto unknown radical ClC(O)S • , and subsequent decomposition of this radical to give either the ClCO • radical or the OCS molecule. By contrast, ClC(O)SCH 3 decomposes in two steps, the first consisting of fragmentation to CO and ClSCH 3 , and the second entailing detachment of a hydrogen atom from the methyl group of ClSCH 3 with the formation of the molecular complex H 2 CdS‚‚‚HCl. The IR spectra of both the ClC(O)S • radical and H 2 CdS‚‚‚HCl have been interpreted with reference to the spectra predicted by ab initio and density functional theory methods.

The structures and conformational behaviour of the sulfenyl carbonyl compounds ClC(O)SCl and ClC(O)SCH 3 have been investigated in the gas and crystalline states by a combination of quantum chemical (HF, MP2 and DFT approximations with the 6-31+G* basis set) calculations, IR studies of the matrixisolated molecules, and X-ray crystallographic analysis of single crystals at low temperatures. Hence the predominance of the syn rotamer in the vapour of each compound has been confirmed; the anti rotamer must account for less than 1% of the vapour molecules. The crystals of the compounds are each composed exclusively of the planar syn rotamer with overall C s symmetry.y RMR and CODV are members of the Carrera del Investigador Cientı ´fico del Consejo Nacional de Investigaciones Cientı ´ficas y Te ´cnicas, Repu ´blica Argentina.

The four-membered heterocyclic beta-propiothiolactone compound was isolated in a low-temperature inert Ar matrix, and the UV-visible (200 < or = lambda < or = 800 nm) induced photochemistry was studied. On the basis of the IR spectra, the formation of methylketene (CH(3)CHCO) was identified as the main channel of photodecomposition. The formation of ethene and thiirane, with the concomitant elimination of OCS and CO, respectively, was also observed as minor decomposition channels. The valence electronic structure was investigated by HeI photoelectron spectroscopy assisted by quantum chemical calculations at the OVGF/6-311++G(d,p) level of theory. The first three bands at 9.73, 9.87, and 12.06 eV are ascribed to the n''(S), n'(O), and pi''(CO) orbitals, respectively, denoting the importance of the -SC(O)- group in the outermost electronic properties. Additionally, the structure of a single crystal, grown in situ, was determined by X-ray diffraction analysis at low temperature. The crystalline solid [monoclinic system, P21/c, a = 8.1062(1) A, b = 10.3069(2) A, c = 10.2734(1) A, beta = 107.628(1) degrees, and Z = 8] consists of planar molecules arranged in layers. The skeletal parameters, especially the valence angles [angleC2-C1-S = 94.55(7) degrees, angleOC-C = 134.20(11) degrees, angleC-S-C = 77.27(5) degrees], differ from those typically found in acyclic thioester compounds, suggesting the presence of strong strain effects. The conventional ring strain energy was determined to be 16.4 kcal/mol at the G2MP2 level of calculation within the hyperhomodesmotic model.

Total and partial ion yield spectra of chlorocarbonylsulfenyl chloride, ClC(O)SCl, are studied using tunable synchrotron radiation. Multicoincidence techniques, which include photoelectron-photoion coincidence (PEPICO) and photoelectron-photoion-photoion coincidence (PEPIPICO) time-of-flight mass spectrometry, were applied to study the fragmentation dynamics around the S 2p, Cl 2p, C 1s, and O 1s ionization edges. The search for site-specific fragmentation effects showed a definite enhancement of the Cl+ signal at the Cl 2p resonance. However, fragmentation patterns of the PEPICO spectra at the various excitation energies are essentially identical. Evidence for the occurrence of the previously reported charge separation after an ion rearrangement dissociation mechanism was found. Highly charged species were observed in the multicoincidence spectra at K shell transitions, revealing the formation of a highly charged molecular ion.

Weakly bound 1:1 complexes formed between CO and a dihalogen molecule XY ) Cl 2 , BrCl, ICl, or IBr have been investigated by matrix-isolation experiments and density functional theory (DFT) calculations. Two families of these linear complexes exist according to whether the C or the O atom of the CO binds to the dihalogen, and with a heteronuclear dihalogen XY, this binding may occur to either of the dihalogen atoms, giving four possible isomeric forms. In addition to the ν(CO) modes of the various complexes, IR measurements have identified ν(XY) modes for the complexes of the type OC‚‚‚XY. The structures, vibrational properties, and binding energetics of the complexes are analyzed in light of related studies.