2013) Conformational preferences for some 3,3-bis[(4′-substituted phenylsulfanyl)]1-methyl-2-piperidinones through spectroscopic and theoretical studies, Journal of Sulfur Chemistry, 34:6, 617-626,The analysis of the IR carbonyl band of some 3,3-bis[(4 -substituted phenylsulfanyl)]1-methyl-2-piperidinones 1-5 bearing as substituents OMe 1, Me 2, H 3, Cl 4 and Br 5, supported by B3LYP/6-31G(d,p) calculations for 3, indicated the existence of three conformers in the gas phase and practically a single conformer in solution. In the gas phase, the c 1 conformer is less polar and slightly more stable than the most polar c 2 conformer. The c 3 conformer is the least polar and least stable conformer. The summing up of the selected natural bond orbital delocalization orbital energies is practically the same (ca.136 kcal mol −1 ) for the c 1 , c 2 and c 3 conformers of 3. Therefore, the trend of the [O δ− (CO) · · · H δ+ o−Ph ] (hydrogen bond) attractive electrostatic interactions along with the trend of the [O δ− (CO) · · · S δ− ] repulsive electrostatic interactions are the main factors which determine the observed computed relative populations for the c 1 (44%), c 2 (31%) and c 3 (25%) conformers. Moreover, the IR single carbonyl stretching band found (for 1-5) in solvents of increasing relative permissivity (CCl 4 , CHCl 3 , CH 2 Cl 2 , CH 3 CN), in agreement with polarisable continuum model calculations (for 3), show that the most polar c 2 conformer is practically unique in the solution (for 1-5), and the geometry is very close to that of the c 2 conformer in the solid state (for 1-4). = H = C = N = O = S Y = OMe 1, Me 2, H 3, Cl 4, Br 5 Most polar conformer (c 2 ) Y Y
Abstract:The analysis of the IR carbonyl bands of some 3-(4′-substituted phenylsulfanyl)-1-methyl-2-piperidones 1-6 bearing substituents: NO 2 (compound 1), Br (compound 2), Cl (compound 3), H (compound 4) Me (compound 5) and OMe (compound 6) supported by B3LYP/6-31+G(d,p) and PCM calculations along with NBO analysis (for compound 4) and X-ray diffraction (for 2) indicated the existence of two stable conformations, i.e., axial (ax) and equatorial (eq), the former corresponding to the most stable and the least polar one in the gas phase calculations. The sum of the energy contributions of the orbital interactions (NBO analysis) and the electrostatic interactions correlate well with the populations and the ν CO frequencies of the ax and eq conformers found in the gas phase. Unusually, in solution of the non-polar solvents n-C 6 H 14 and CCl 4 , the more intense higher IR carbonyl frequency can be ascribed to the ax conformer, while the less intense lower IR doublet component to the eq one. The same ν CO frequency trend also holds in polar solvents, that is ν CO (eq) < ν CO (ax) . However, a reversal of the ax/eq intensity ratio occurs going from non-polar to polar solvents, with the ax conformer component that OPEN ACCESSMolecules 2013, 18 7493 progressively decreases with respect to the eq one in CHCl 3 and CH 2 Cl 2 , and is no longer detectable in the most polar solvent CH 3 CN. The PCM method applied to compound 4 supports these findings. In fact, it predicts the progressive increase of the eq/ax population ratio as the relative permittivity of the solvent increases. Moreover, it indicates that the computed ν CO frequencies of the ax and eq conformers do not change in the non-polar solvents n-C 6 H 14 and CCl 4 , while the ν CO frequencies of the eq conformer become progressively lower than that of the ax one going from CHCl 3 to CH 2 Cl 2 and to CH 3 CN, in agreement with the experimental IR values. The analysis of the geometries of the ax and eq conformers shows that the carbonyl oxygen atom of the eq conformer is free for solvation, while the O [CO] … H [o-Ph] hydrogen bond that takes place in the ax conformer partially hinders the approach of the solvent molecules to the carbonyl oxygen atom. Therefore, the larger solvation that occurs in the carbonyl oxygen atom of the eq conformer is responsible for the observed and calculated decrease of the corresponding frequency. The X-ray single crystal analysis of 2 indicates that this compound adopts the most polar eq geometry in the solid. In fact, in order to obtain the largest energy gain, the molecules are arranged in the crystal in a helical fashion due to dipole moment coupling along with C-H … O and C-H … π Ph hydrogen bonds.
In the title compound, C18H17Br2NOS2, the conformation of the piperidin-2-one ring is based on a half-chair with the methylene C atom diagonally opposite the N atom being 0.649 (3) Å above the plane of the remaining five atoms (r.m.s. deviation = 0.1205 Å). The S atoms occupy axial and bisectional positions, and the dihedral angle between the benzene rings of 59.95 (11)° indicates a splayed disposition. Helical supramolecular chains along the b axis sustained by C—H⋯O interactions is the major feature of the crystal packing. The chains are connected into a three-dimensional architecture by C—H⋯Br and C—H⋯π interactions.
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