Conformational stabilities of 1-methoxy-2-(methylthio)ethane and relevant intramolecular CH⋯O interaction studied by matrix-isolation infrared spectroscopy and density functional calculations

Conformational stabilities of 1-methoxy-2-(methylthio)ethane were studied by matrix-isolation infrared spectroscopy, and the relevant intramolecular 1,5-CH⋯O interaction was examined by density functional calculations. The conformer with trans–trans–gauche± around the CH3O–CH2–CH2–SCH3 bonds is the most stable in an argon matrix and the conformer with trans–gauche±–gauche∓ is the second most stable. The energy difference between the two conformers was determined to be 0.7±0.4 kJ mol−1 using thermal effusive sources. The 1,5-CH⋯O interaction is responsible for the high stability of the trans–gauche±–gauche∓ conformer, since the nonbonded (C)H⋯O distance associated with this interaction is shorter than the corresponding van der Waals separation by 0.15 Å. The energy of the 1,5-CH⋯O interaction was evaluated to be 4.0 kJ mol−1.