Carlos R. Cerqueira

1-Methyl-3-phenyl-sulfonyl-2-piperidone.

The piperidone ring in the title compound, C12H15NO3S, has a slightly distorted half-chair conformation with the methyl, carbonyl and phenylsulfonyl ring substituents occupying equatorial, equatorial and axial positions, respectively. Molecules are connected into centrosymmetric dimers via C—H⋯O interactions and these associate into layers via C—H⋯O—S contacts. Further C—H⋯O interactions involving both the carbonyl and sulfonyl O atoms consolidate the crystal packing by providing connections between the layers.

Spectroscopic and Theoretical Studies of Some 3-(4'-Substituted phenylsulfanyl)-1-methyl-2-piperidones

The analysis of the IR carbonyl bands of some 3-(4′-substituted phenylsulfanyl)-1-methyl-2-piperidones 1–6 bearing substituents: NO2 (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 νCO frequencies of the ax and eq conformers found in the gas phase. Unusually, in solution of the non-polar solvents n-C6H14 and CCl4, 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 νCO frequency trend also holds in polar solvents, that is νCO (eq) < νCO (ax). However, a reversal of the ax/eq intensity ratio occurs going from non-polar to polar solvents, with the ax conformer component that progressively decreases with respect to the eq one in CHCl3 and CH2Cl2, and is no longer detectable in the most polar solvent CH3CN. 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 νCO frequencies of the ax and eq conformers do not change in the non–polar solvents n-C6H14 and CCl4, while the νCO frequencies of the eq conformer become progressively lower than that of the ax one going from CHCl3 to CH2Cl2 and to CH3CN, 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…πPh hydrogen bonds.

Conformational preferences for some 3,3-bis[(4′-substituted phenylsulfanyl)]1-methyl-2-piperidinones through spectroscopic and theoretical studies

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 c1 conformer is less polar and slightly more stable than the most polar c2 conformer. The c3 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 c1, c2 and c3 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 c1 (44%), c2 (31%) and c3 (25%) conformers. Moreover, the IR single carbonyl stretching band found (for 1–5) in solvents of increasing relative permissivity (CCl4, CHCl3, CH2Cl2, CH3CN), in agreement with polarisable continuum model calculations (for 3), show that the most polar c2 conformer is practically unique in the solution (for 1–5), and the geometry is very close to that of the c2′ conformer in the solid state (for 1–4). GRAPHICAL ABSTRACT

3,3-Bis[(4-chlorophenyl)sulfanyl]-1-methylpiperidin-2-one.

The piperidone ring in the title compound, C18H17Cl2NOS2, has a distorted half-chair conformation. The S-bound benzene rings are approximately perpendicular to and splayed out of the mean plane through the piperidone ring [dihedral angles = 71.86 (13) and 46.94 (11)°]. In the crystal, C—H⋯O interactions link the molecules into [010] supramolecular chains with a helical topology. C—H⋯Cl and C—H⋯π interactions are also present.

Crystal and molecular structures of three 2-sulphur-substituted cyclohexanones studied by X-ray crystallography and by ab initio molecular orbital calculations

Abstract The conformational features of three 2-sulphur-substituted cyclohexanone derivatives, which differ in the number of sulphur-bound oxygen atoms, i.e. zero (I), one (II) and two (III), were investigated by single crystal X-ray crystallography and geometry optimized structures determined using Hartree-Fock method. In each of (I)–(III) an intramolecular S … Ocarbonyl interaction is found with the magnitude correlated with the oxidation state of the sulphur atom, i.e. 2.838(3) Å in (I) to 2.924(2) Å in (II) to 3.0973(18) Å in (III). There is an inverse relationship between the strength of this interaction and the magnitude of the carbonyl bond. The supramolecular aggregation patterns are primarily determined by C–H … O contacts and are similarly influenced by the number of oxygen atoms in the molecular structures. Thus, a supramolecular chain is found in the crystal structure of (I). With an additional oxygen atom available to participate in C–H … O interactions, as in (II), a two-dimensional array is found. Finally, a three-dimensional network is found for (III). Despite there being differences in conformations between the experimental structures and those calculated in the gas-phase, the S … O interactions persist. The presence of intermolecular C–H … O interactions involving the cyclohexanone-carbonyl group in the solid-state, disrupts the stabilising intramolecular C–H … O interaction in the energetically-favoured conformation. (I): C12H13NO3S, triclinic space group P-1 with a = 5.392(3) Å, b = 10.731(6) Å, c = 11.075(6) Å, α = 113.424(4)°, β = 94.167(9)°, γ = 98.444(6)°, V = 575.5(6) Å3, Z = 2, R1 = 0.052; (II): C12H13NO4S, monoclinic P21/n, a = 7.3506(15) Å, b = 6.7814(14) Å, c = 23.479(5) Å, β = 92.94(3)°, V = 1168.8(4) Å3, Z = 4, R1 = 0.046; (III): C12H13NO5S, monoclinic P21/c, a = 5.5491(11) Å, b = 24.146(3) Å, c = 11.124(3) Å, β = 114.590(10)°, V = 1355.3(5) Å3, Z = 4, R1 = 0.051.

1-(4-Bromo-phen-yl)-2-ethyl-sulfinyl-2-(phenyl-selan-yl)ethanone monohydrate.

In the title hydrate, C16H15BrO2SSe·H2O, the sulfinyl O atom lies on the opposite side of the molecule to the Se and carbonyl O atoms. The benzene rings form a dihedral angle of 51.66 (17)° and are splayed with respect to each other. The observed conformation allows the water molecules to bridge sulfinyl O atoms via O—H⋯O hydrogen bonds, generating a linear supramolecular chain along the b axis; the chain is further stabilized by C—H⋯O contacts. The chains are held in place in the crystal structure by C⋯H⋯π and C—Br⋯π interactions.

3,3-Bis(4-bromo-phenyl-sulfan-yl)-1-methyl-piperidin-2-one.

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.

3,3-Bis[(4-methoxyphenyl)sulfanyl]-1-methylpiperidin-2-one

The piperidone ring in the title compound, C20H23NO3S2, has a distorted half-chair conformation with the central methylene atom of the propyl fragment lying 0.696 (1) Å out of the plane defined by the other five atoms (r.m.s. deviation = 0.071 Å). One of the S-bound phenyl rings is almost perpendicular to the mean plane through the piperidone ring, whereas the other is splayed [dihedral angles = 71.95 (6) and 38.42 (6)°]. In the crystal, C—H⋯O and C—H⋯π interactions lead to the formation of supramolecular layers in the ab plane.

1-Methyl-3,3-bis­(phenyl­sulfan­yl)piperidin-2-one

The piperidone ring in the title compound, C18H19NOS2, is in a distorted half-chair conformation, distorted towards a twisted boat, with the central methylene C atom of the propyl backbone lying 0.606 (2) Å out of the plane defined by the other five atoms (r.m.s. deviation = 0.1197 Å). One of the S-bound phenyl rings is almost perpendicular to the least-squares plane through the piperidone ring, whereas the other is splayed [dihedral angles = 75.97 (6) and 44.21 (7)°, respectively]. The most prominent feature of the crystal packing is the formation of helical supramolecular chains along the b axis sustained by C—H⋯O interactions. The chains are consolidated into a three-dimensional architecture via C—H⋯π interactions whereby one S-bound phenyl ring accepts two C—H⋯π contacts.

1-Methyl-3,3-bis-[(4-methyl-phen-yl)sulfan-yl]piperidin-2-one.

The piperidone ring in the title compound, C20H23NOS2, has a half-chair distorted to a twisted-boat conformation [Q T = 0.5200 (17) Å]. One of the S-bound benzene rings is almost perpendicular to the least-squares plane through the piperidone ring, whereas the other is not [dihedral angles = 75.28 (5) and 46.41 (5) Å, respectively]. In the crystal, the presence of C—H⋯O and C—H⋯π interactions leads to the formation of supramolecular layers in the ab plane.