Anomeric and mesoneric effects in methoxycarbonylsulfenyl chloride, CH3OC(O)SCl. An experimental and theoretical study

Abstract

The molecular structure and conformational properties of methoxycarbonylsulfenyl chloride, CH3OC(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 CdO bond) and the O−CH3 bond synperiplanar with respect to the CdO 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 ∆G° between the syn and anti conformers. The results are discussed in terms of anomeric effects and a natural bond orbital (NBO) calculation. Photolysis of matrixisolated CH3OC(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.