Imidazolidine is a heterocyclic compound

Heterocyclic compound

A heterocyclic compound is a cyclic compound which has atoms of at least two different elements as members of its ring. The counterparts of heterocyclic compounds are homocyclic compounds, the rings of which are made of a single element....

 formally derived by the addition of four hydrogen atoms to imidazole

Imidazole

Imidazole is an organic compound with the formula C3H4N2. This aromatic heterocyclic is a diazole and is classified as an alkaloid. Imidazole refers to the parent compound, whereas imidazoles are a class of heterocycles with similar ring structure, but varying substituents...

. The intermediate, resulting from the addition of only two hydrogen atoms is called dihydroimidazole (imidazoline). The connection of imidazolidine to related compounds is indicated in the Figure.
Formally, removal of the two hydrogens at carbon 2 (between the two nitrogens) would yield the carbene

Carbene

In 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 RR'C:, but the carbon can instead be double-bonded to one group. The term "carbene" may also merely refer to the compound H2C:, also called...

 dihydroimidazol-2-ylidene

Dihydroimidazol-2-ylidene

Dihydroimidazol-2-ylidene is a hypothetical organic compound with formula C3H6N2. It would be a heterocyclic compound, formally derived from imidazolidine with two hydrogen atoms removed from carbon number 2, leaving two vacant chemical bonds — which makes it a carbene.Although carbenes in general...

. Derivatives of the latter comprise an important class of persistent carbene

Persistent carbene

A persistent carbene is a type of carbene demonstrating particular stability. The best-known examples are diaminocarbenes with the general formula 2C:, where the 'R's are various functional groups...

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