Use
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.