Conformational study of some 4'-substituted 2-(phenylselanyl)-2-(ethylsulfanyl)-acetophenones

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.

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

The title compound, C15H13ClO2S, comprises (4-chloro-phen-yl)sulfanyl, benzaldehyde and meth-oxy residues linked at a chiral methine-C atom (the crystal is racemic). A twist in the methine-C-C(carbon-yl) bond [O-C-C-O torsion angle = 19.3 (7)°] leads to a dihedral angle of 22.2 (5)° between the benzaldehyde and methine+meth-oxy residues. The chloro-benzene ring is folded to lie over the O atoms, with the dihedral angle between the benzene rings being 42.9 (2)°. In the crystal, the carbonyl-O atom accepts two C-H⋯O inter-actions with methyl- and methine-C-H atoms being the donors. The result is an helical supra-molecular chain aligned along the c axis; chains pack with no directional inter-actions between them. An analysis of the Hirshfeld surface points to the important contributions of weak H⋯H and C⋯C contacts to the mol-ecular packing.