Chirality, structure and hydrogen bonding in dithiols: Rotational spectrum of the chiral and meso 2,3-butanedithiol

Abstract

We have characterized the homochiral (2R, 3R) and heterochiral meso (2R,3S) isomers of 2,3-butanedithiol, using rotational spectroscopy at centimeter and millimeter-wave frequencies. The microwave experiment used jet-cooled chirped-pulsed fast-passage excitation in the range 2–8 GHz, while the millimeter-wave measurements in the regions 75–129 and 170–300 GHz used source modulation and lock-in detection at room temperature. A single rotamer was observed for each structural isomer, more intense for the homochiral species. The homochiral carbon skeleton is antiperiplanar and differs from the synclinal skeleton of the heterochiral isomer. However, the two rotamers share synclinal sulfur atoms which permit S-H··⋅S intramolecular hydrogen bonds, illustrating chirality-dependent synchronization. Density functional theory methods (B3LYP and B2PLYP) with (D3) dispersion corrections complemented the experimental work. Additionally, the presence of intramolecular interactions was assessed with an analysis of the reduced electronic density gradient with the NCIPlot method, which suggested both S-H⋅⋅⋅S and weak C-H⋅⋅⋅S interactions.