Persistent carbene

A persistent carbene (also known as stable carbene) is an <a href="/facts/Organic_molecule/gqCNaN45">organic molecule</a> whose natural <a href="/facts/Resonance_structure/5tymwoIP">resonance structure</a> has a carbon atom with <a href="/facts/Octet_rule/X9jxSsos">incomplete octet</a> (a <a href="/facts/Carbene/3WxNSStY">carbene</a>), but does not exhibit the tremendous instability typically associated with such moieties. The best-known examples and by far largest subgroup are the N-heterocyclic carbenes (NHC) (sometimes called Arduengo carbenes), in which nitrogen atoms flank the formal carbene.
Modern theoretical analysis suggests that the term "persistent carbene" is in fact a <a href="/facts/Misnomer/P4TnsX3H">misnomer</a>. Persistent carbenes do not in fact have a carbene electronic structure in their <a href="/facts/Ground_state/ML7cfCug">ground state</a>, but instead an <a href="/facts/Ylide/WcfsUPR7">ylide</a> stabilized by <a href="/facts/Aromaticity/wK0DzRY6">aromatic resonance</a> or <a href="/facts/Steric_shielding/TnX5c8HG">steric shielding</a>. Acid catalyzes the carbene-like dimerization that some persistent carbenes undergo over the course of days.
Persistent carbenes in general, and Arduengo carbenes in particular, are popular <a href="/facts/Ligand/6etB3qeW">ligands</a> in <a href="/facts/Organometallic_chemistry/bhqFz2P0">organometallic chemistry</a>.

Persistent carbene open-in-new

Persistent carbene