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 NO 2 1a , Br 2a , H 3a , Me 4a and OMe 5a for the C R S R /C S S S enantiomeric pair and Br 2b and Me 4b for the C R S S /C S S R pair. The theoretical data indicated the existence of three stable conformations for the C R S R series and two for the C R S S 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 ν CO 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 , LP O(S-O)  → σ* C-H(CH2Me) and LP O(S-O)  → σ* C-H( o -PhSe) . The XRD analysis indicates that the major component of 3a (C R S R ) matches the geometry of the intermediate stable c 2 conformer. Similarly, the solid-state structure of 2b (C R S S ) corresponds to the less stable c 2 conformer. The molecules in the solid are linked in centrosymmetrical pairs through π … π interactions between Se-bound phenyl rings, along with phenyl-C H…O (carbonyl and sulphinyl) interactions.