A sulfoxide is a chemical compound containing a sulfinyl (SO) functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are the oxidized derivatives of sulfides. Examples of important sulfoxides are alliin, a precursor to the compound that gives freshly crushed garlic its aroma, and DMSO, a common solvent.
Sulfoxides are characterized by pyramidal sulfur center with relatively short S-O distances.
Dimensions of dimethylsulfoxide.
Sulfoxides are generally represented with the structural formula R–S(=O)–R', where R and R' are organic groups. The bond between the sulfur and oxygen atoms is intermediate of a dative bond and a polarized double bond. The S–O interaction has an electrostatic aspect, resulting in significant dipolar character, with negative charge centered on oxygen. A lone pair of electrons resides on the sulfur atom giving it tetrahedral geometry if one considers the lone pair or trigonal pyramidal if the lone pair is ignored.(See VSEPR theory) When the two organic residues are dissimilar, the sulfur is a chiral center, for example, methylphenylsulfoxide.
The energy required to invert this stereocenter is sufficiently high that sulfoxides are optically stable, that is, the rate of racemization is slow at room temperature.
^R. Thomas, C. B. Shoemaker and K. Eriks "The molecular and crystal structure of dimethyl sulfoxide, (H3C)2SO Acta Cryst. 1966, vol. 21, 12-20. doi:10.1107/S0365110X66002263,
^Terence P. Cunningham, David L. Cooper, Joseph Gerratt, Peter B. Karadakov and Mario Raimondi (1997). "Chemical bonding in oxofluorides of hypercoordinate sulfur". Journal of the Chemical Society, Faraday Transactions93 (13): 2247–2254. doi:10.1039/A700708F.
^Kathrin-Maria Roy “Sulfones and Sulfoxides” Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a25_487
^Mario Calligaris "Structure and bonding in metal sulfoxide complexes: an update" Coordination Chemistry Reviews 2004, vol. 248, pp. 351-375. doi:10.1016/j.ccr.2004.02.005
^Oxidation of sulfides to chiral sulfoxides using Schiff base-vanadium (IV) complexes Ángeles Gama, Lucía Z. Flores-López, Gerardo Aguirre, Miguel Parra-Hake, Lars H. Hellberg, and Ratnasamy Somanathan Arkivoc MX-789E 2003Online article