Carbene

Definition

A transient species of the form RR′C:, with two valence electrons that do not form bonds. The simplest example is methylene, H₂C:. Carbenes are short-lived intermediates in some organic reactions. They attack double bonds to form three-membered rings (i.e. cyclopropane derivatives). They also attack single bonds in insertion reactions, for example: R–O–H + R₂C: → R-O-C(R₂)H R–H + R₂C: → R–C(R₂)-H Carbenes are important ‘reagents’ in organic synthesis and various methods exist for generating them in the reaction medium.

Definition

An organic radical containing divalent carbon. Some divalent-carbon derivatives where the carbon is multiple bonded to oxygen or nitrogen are stable compounds (carbon monoxide); most are highly reactive units known only as reaction intermediates. Carbenes, carbonium ions, carbanions, and free radicals are the four most important classes of organic reaction intermediates containing carbon in an unstable valence state. A typical synthesis involving a carbene is that of cyclopropanes by the addition of carbenes to olefins.

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Preparation Products