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

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

Author Olivato, Paulo R. Google Scholar
Santos, Jean M. M. Google Scholar
Contieri, Bruna Google Scholar
Cerqueira, Carlos R. Google Scholar
Rodrigues, Daniel N. S. Google Scholar
Vinhato, Elisangela Autor UNIFESP Google Scholar
Zukerman-Schpector, Julio Google Scholar
Dal Colle, Maurizio Google Scholar
Institution Universidade de São Paulo (USP)
Universidade Federal de São Paulo (UNIFESP)
Universidade Federal de São Carlos (UFSCar)
Univ Ferrara
Abstract 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 vCO 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.CO frequency trend also holds in polar solvents, that is nu(CO(eq)) < nu(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 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.CO frequencies of the ax and eq conformers do not change in the non-polar solvents n-C6H14 and CCl4, while the.CO 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]center dot center dot center dot 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 center dot center dot center dot O and C-H center dot center dot center dot pi(Ph) hydrogen bonds.
Keywords conformational analysis
infrared spectroscopy
theoretical calculations
3-(4 '-substituted phenylsulfanyl)-1-methyl-2-piperidones
X-ray crystal structure
Language English
Sponsor Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
MIUR (PRIN)
Grant number CAPES: 808/2009
Date 2013-07-01
Published in Molecules. Basel: Mdpi Ag, v. 18, n. 7, p. 7492-7509, 2013.
ISSN 1420-3049 (Sherpa/Romeo, impact factor)
Publisher Mdpi Ag
Extent 7492-7509
Origin http://dx.doi.org/10.3390/molecules18077492
Access rights Open access Open Access
Type Article
Web of Science ID WOS:000330300900012
URI http://repositorio.unifesp.br/handle/11600/36459

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