Carbene

This article is about the chemical class. For the compound, see Methylene (compound).
Not to be confused with carbine or carbyne.
Methylene is the simplest carbene.

In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is R−:C−R' or R=C: where the R represents substituents or hydrogen atoms.

The term "carbene" may also refer to the specific compound :CH2, also called methylene, the parent hydride from which all other carbene compounds are formally derived.[1][2]

There are two types of carbenes: singlets or triplets, depending upon their electronic structure.[3] The different classes undergo different reactions.

Most carbenes are extremely reactive and short-lived. A small number (the dihalocarbenes, carbon monoxide,[4] and carbon monosulfide) can be isolated, and can stabilize as metal ligands, but otherwise cannot be stored in bulk. A rare exception are the persistent carbenes,[5] which have extensive application in modern organometallic chemistry.

  1. ^ Hoffmann, Roald (2005). Molecular Orbitals of Transition Metal Complexes. Oxford. p. 7. ISBN 978-0-19-853093-0.
  2. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "carbenes". doi:10.1351/goldbook.C00806
  3. ^ Grossman, Robert B. (2003). The Art of Writing Reasonable Organic Reaction Mechanisms (2nd ed.). New York: Springer. p. 84. ISBN 0-387-95468-6.
  4. ^ Grossman 2003, p. 35.
  5. ^ For detailed reviews on stable carbenes, see: (a) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G. (2000). "Stable Carbenes". Chem. Rev. 100 (1): 39–91. doi:10.1021/cr940472u. PMID 11749234. (b) Melaimi, M.; Soleilhavoup, M.; Bertrand, G. (2010). "Stable cyclic carbenes and related species beyond diaminocarbenes". Angew. Chem. Int. Ed. 49 (47): 8810–8849. doi:10.1002/anie.201000165. PMC 3130005. PMID 20836099.