Conformational analysis and electronic interactions of 2-thiosubstituted cyclohexanones by semilempirical method PM3

摘要

Some 2-phenylthio-para-substituted cyclohexanones with different oxidation states of sulfur atom were studied by systematic conformational search around C-S bonds using the parametric method 3 (PM3) Hamiltonian. The axial and equatorial regular chair conformations were subjected to calculations and each one produced three rotamers: +gauche (+G), -gauche (-G), and anti (A). The axial conformations were more populated than the equatorial ones. The para-substituent and sulfur group effects over conformational populations and carbonyl polarizations suggest that the main electronic interaction between sulfur atom and carbonyl group are of repulsive nature in both axial (such as S+C+O) and equatorial (such as S-CO-) conformations. The axial +G conformation is the more stable for all compounds, except for (R-2,S-S)-sulfinyl isomer, because it allows an attractive electrostatic interaction between C-O and S-O bond dipoles (such as S+CO-). The axial A conformation is the more stable for (R,,S,)-sulfinyl compounds, because the sulfinyl oxygen is at -G position near the carbonyl group and an attractive electrostatic interaction (such as O-SO(-) C+O) can take place. The higher carbonyl polarization and negative charge of carbon C-2 plus hydrogen H-2 of cyclohexanone ring for sulfonyl compared with sulfanyl and sulfinyl compounds, can be explained by a through-space interaction instead through-bond inductive effects. (C) 2003 Wiley Periodicals, Inc. [References: 14]