Solid and liquid phase Raman and infrared spectra of diallyl sulfide and diallyl disulfide

The Raman and IR spectra of diallyl sulfide and diallyl disulfide in the liquid and solid state are reported and examined in order to determine their most stable conformations. In both the liquid and solid state, the allyl moieties in both molecules are in a “gauche” conformation in which the sulfur atoms and the terminal vinyl carbons probably form a dihedral angle of between 105° and 120°. In the liquid state, there are two possible S-S rotational conformers of diallyl disulfide. The “gauche” conformer with a C-S-S-C dihedral angle of approximately 70° is 242±24 cal mol−1 more stable than the “near-cis” conformer which probably has a C-S-S-C dihedral angle of approximately 25°. Only the “gauche” S-S rotational conformer of diallyl disulfide exists in the solid state. Additionally, in the liquid state, there are two C-S rotational conformers for each molecule. The “gauche” conformer corresponds to a C-C-S-C (diallyl sulfide) or C-C-S-S (diallyl disulfide) dihedral angle of 70° and the “trans” conformer corresponds to a C-C-S-C or C-C-S-S dihedral angle of 180°. For diallyl sulfide the “trans” C-S conformer is 260±26 cal mol−1 more stable than the “gauche” C-S conformer while for diallyl disulfide the “gauche” C-S conformer is 358±20 cal mol−1 more stable than the “trans” C-S conformer. In the solid state, both C-S conformers exist for diallyl sulfide but only the “gauche” C-S conformer exists for diallyl disulfide.