2-[(4-Chloro-phen-yl)sulfan-yl]-2-meth-oxy-1-phenyl-ethan-1-one: crystal structure and Hirshfeld surface analysis

Conformationally Biased Ketones React Diastereoselectively with Allylmagnesium Halides

The addition of the highly reactive reagent allylmagnesium halide to α-substituted acyclic chiral ketones proceeded with high stereoselectivity. The stereoselectivity cannot be analyzed by conventional stereochemical models because these reactions do not conform to the requirements of those models. Instead, the stereoselectivity arises from the approach of the nucleophile to the most accessible diastereofaces of the lowest-energy conformations of the ketones. High stereoselectivity is expected, and the stereochemical outcome can be predicted, with conformationally biased ketones that have sterically distinguishable diastereofaces wherein only one face is accessible for nucleophilic addition. The conformations of the ketones can be determined by a combination of computational modeling and, in some cases, structure determination by X-ray crystallography.

Spectroscopic and theoretical studies of some 2‑(methoxy)‑2‑[(4‑substituted)‑phenylsulfanyl]‑(4'‑substituted) acetophenones

The conformational analysis of some 2‑(methoxy)‑2‑[(4‑substituted)‑phenylsulfanyl]‑(4'‑substituted) acetophenones was performed through infrared (IR) spectroscopic analysis of the carbonyl stretching band (ν_CO), supported by B3LYP/6-31+G(d,p) calculations and X-ray diffraction. Five (1-5) of the seven studied compounds (1-7) presented Fermi resonance (FR) on the ν_CO fundamental transition band. Deuteration of these compounds (1a-5a) precluded the occurrence of FR, revealing a ν_CO doublet for all compounds in all solvents used. The computational results indicated the existence of three conformers (c₁, c₂ and c₃) for the whole series whose relative abundances varied with solvent permittivity. The higher ν_CO frequency c₁ conformer was assigned to the higher frequency component of the carbonyl doublet, while both c₂ and c₃ were assigned to the lower frequency one. Anharmonic vibrational frequencies and Potential Energy Distribution (PED) calculations of compound 3 indicated that the combination band (cb) between the methyne δ_CH and one skeletal mode couples with the ν_CO mode giving rise to the FR on the c₂ conformer in vacuum and on the c₁ one in non-polar solvents. The experimental data indicated a progressive increase in c₁ conformer stability with the increase of the solvent dielectric constant, which is in good agreement with the polarizable continuum model (PCM) calculations. The higher ν_CO frequency and the stronger solvation of the c₁ conformer is a consequence of the repulsive field effect (RFE) originated by the alignment and closeness of the C^δ+O^δ- and C^δ+O^δ- dipoles. Finally, the balance between orbital and electrostatic interactions dictates the conformational preferences. X-ray single crystal analysis for compound 6 revealed the c₁ geometry in the solid state and its stabilization by CH…O hydrogen bonds.