Exploring the intra- and intermolecular disulfide-centered non-covalent interactions in methyl allyl disulfide and its complex with water

The conformations of methyl allyl disulfide and its water adduct were studied experimentally by rotational spectroscopy supported by quantum chemical calculations. For the monomer, two conformers of methyl allyl disulfide, being stabilized by intramolecular S⋯π and CH⋯π interactions, are observed in a helium supersonic expansion. The measurement of the singly heavy atom substituted isotopologues (four 13C and two 34S isotopologues for the most stable monomer conformer and two 34S isotopologues for the second stable conformer) facilitates an accurate determination of the molecular structures. One isomer of the methyl allyl disulfide⋯water complex was identified. The observed conformation involves the most stable monomer conformer, wherein the water molecule forms one OH⋯S–S and one bifurcated CH⋯O hydrogen bond with the methyl allyl disulfide moiety. The OH⋯S–S interaction, with an energy of 29.5 kJ mol−1, is significantly stronger than the CH⋯O contact, which has energies of 3.3 and 3.6 kJ mol−1, respectively, and plays a major role in the formation of the complex. The nature of these intra- and intermolecular disulfide-centered non-covalent interactions was quantitatively revealed by the combination of accurate structural determination, natural bond orbital analysis, and energy decomposition analysis.