text: 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  or  where the R represents substituents or hydrogen atoms.
  The term "carbene" may also refer to the specific compound , also called methylene, the parent hydride from which all other carbene compounds are formally derived. 
  There are two types of carbenes: singlets or triplets, depending upon their electronic structure.  The different classes undergo different reactions.  
  Most carbenes are extremely reactive and short-lived.  A small number (the dihalo<nowiki/>carbenes, carbon monoxide, 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, which have extensive application in modern organometallic chemistry.