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

• Published in: Journal of molecular structure Vol. 1133; pp. 49 - 65
• Main Authors: Cerqueira, Carlos R., Olivato, Paulo R., Rodrigues, Daniel N.S., Zukerman-Schpector, Julio, Tiekink, Edward R.T., Dal Colle, Maurizio
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05-04-2017
• Subjects: 4′-substituted 2-(phenylselanyl)-2-(ethylsulfinyl)-acetophenones; Infrared spectroscopy; Solvent effect; Stereochemical isomerism; Theoretical calculations; X-ray diffraction; Solvent effect; X-ray diffraction; Infrared spectroscopy; 4′-substituted 2-(phenylselanyl)-2-(ethylsulfinyl)-acetophenones; Theoretical calculations; Stereochemical isomerism
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2016.11.077

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.
Most stable conformer for the diastereomers CRSR [Y = NO2(1a), Br(2a), H(3a), Me(4a), OMe(5a)] and CRSS [Y = Br(2b), Me(4b)] in the gas phase. [Display omitted]
•The title compounds present (CRSR/CSSS) (I) and (CRSS/CSSR) (II) diastereomers.•Calculations indicate: three and two conformers for (I) and (II), respectively.•A good match was found between the experimental and theoretical data.•Conformer stability and frequency are controlled by coulombic and orbital interactions.•The major X-ray component of (I) assumes the c2 conformation in the gas phase.