Stereoelectronic effects in alpha-carbanions of conformationally constrained sulfides, sulfoxides, and sulfones.
Stabilizing effects in oxygenated thiane- and 1,3-dithiane-derived alpha-carbanions were investigated computationally. All isomers bearing sulfide, sulfoxide, and sulfone functional groups and combinations thereof were investigated by DFT calculations and NBO analyses. Their stabilities and the stereoelectronic effects present in these compounds were compared. Stabilizing effects of the respective functional groups were further estimated by calculation of isodesmic reactions. It turned out that n(C) --> sigma*(S-O) interactions, where both the n(C) and the S=O bond are in an antiperiplanar conformation, have the highest stabilizing effects. Similar stabilizing interactions are effective in carbanions with an equatorial lone pair at the carbon; here a productive n(C) --> sigma*(S-C) interaction is possible. n(C) --> sigma*(S-O) interactions, where the S=O bond is part of a sulfoxide are significantly more effective than in sulfones. Calculations of isodesmic reactions show similar trends but suggest the presence of additional electrostatic effects and possibly, to some extent, steric effects.
Podlech
Joachim
J
Institut für Organische Chemie, Karlsruher Institut für Technologie (KIT), Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany. joachim.podlech@kit.edu