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 chemical 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 molecular geometry as for sp³ carbon. 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.
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