Stereochemical and electronic interaction studies of 4′-substituted 2-(phenylselanyl)-2-(ethylsulfinyl)-acetophenones

Abstract

Infrared carbonyl band analysis, supported by B3LYP/6-31 + G(d,p) and single-point PCM calculations, natural bond orbital (NBO) analysis and X-ray diffraction (XRD) were carried out for the diastereoisomers of a selection of 4′-substituted 2-(phenylselanyl)-2-(ethylsulfinyl)-acetophenones bearing the substituents NO21a, Br 2a, H 3a, Me 4a and OMe 5a for the CRSR/CSSS enantiomeric pair and Br 2b and Me 4b for the CRSS/CSSR pair. The theoretical data indicated the existence of three stable conformations for the CRSR series and two for the CRSS series. For both series, the single-point PCM calculations showed that the relative abundance of the less stable conformers in the gas phase progressively increases as the dielectric constant of the media increases. For compounds 1a–5a, the balance between the electrostatic and orbital interactions controls the calculated stability, as well as the νCO frequency order. Conversely, the more stable conformer in the 2b and 4b compounds is mainly stabilised by the additional orbital interactions LP(S) → σ*C-Se, LPO(S-O) → σ*C-H(CH2Me) and LPO(S-O) → σ*C-H(o-PhSe). The XRD analysis indicates that the major component of 3a (CRSR) matches the geometry of the intermediate stable c2 conformer. Similarly, the solid-state structure of 2b (CRSS) corresponds to the less stable c2 conformer. The molecules in the solid are linked in centrosymmetrical pairs through π … π interactions between Se-bound phenyl rings, along with phenyl-CH…O (carbonyl and sulphinyl) interactions.