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

Abstract

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.

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

“…In addition, the σ* C-S (3.25 eV) [18] electron-affinity energy is higher than that of σ* C-O (6.0 eV [19] or 4.2 eV [20,21]). Therefore, as shown in our previous papers [12][13][14][15][16], then X→ π* CO , σ C-X→ π* CO , π CO→ σ* C-X interactions are stronger in the gauche (axial) conformer(s) of the α-thio-carbonyl compounds (X = S) than for the analogous conformer in the α-oxa-acetophenones (X = O).…”

“…In the last thirty years, the conformational analysis of several different carbonyl compounds performed by our research group, based on a number of spectroscopic (IR, UV, NMR, UPS and ETS) and X-ray studies supported by theoretical calculations, disclosed some relevant findings. The studies of some (α-alkylthio)-and (α-phenylthio)acetones, acetophenones, N,N-diethylamides, esters, thioesters [12,13], N-methoxy-Nmethyl amides [14], and N-methyl-δ-valerolactams [15], indicated that the simultaneous occurrence of the n S →π* CO ,  C-S →π* CO , and π CO →* C-S orbital interactions is the main controlling factor that determines the preference of the gauche (axial) conformer(s) over the cis (equatorial) one(s).…”

“…Harmonic, anharmonic unperturbed and perturbed frequencies (cm -1 ) of the ν CO(15), δ CH(32) and the skeletal (72) vibrational modes and mechanical ν CO anharmonicity (cm -1 ) of 3 obtained at the B3LYP / 6-31+G(d,p) level in vacuum.…”

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

“…Previous reports from this laboratory of IR, UV, NMR and electron spectroscopies studies, supported by theoretical calculations of some (α-alkylthio)-and (α-phenylthio)acetones, acetophenones, N,N-diethylamides, esters, thioesters [1,2], N-methoxy-Nmethyl amides [3], and N-methyl-δ-valerolactams [4], indicated that the simultaneous occurrence of the nS→π*CO, sC-S→π*CO and πCO→s*C-S orbital interactions is the main controlling factor that determines the preference of the gauche (axial) conformer(s) over the cis (equatorial) one(s).…”

Influence of electron acceptors on the kinetics of metoprolol photocatalytic degradation in TiO2 suspension. A combined experimental and theoretical study

“…11,12,[53][54][55][56] The signicance of the chemical or physical interactions between MET and radical species can be assessed by using the total sum of the delocalization energies, P E(2), obtained by summing the electron delocalization energies of all the signicant interactions between the NBO orbitals of interacting molecules. 57,58 The P E(2) values are reported in Table 3. A larger P E(2) means that the interactions, resulting from electron delocalization 2) values are a measure of the importance of chemical interaction between the investigated species.…”