Idene

Idene is a term used in chemistry to denote a class of divalent, double-bonded fragments that can serve as substituents or ligands in larger molecules. In systematic nomenclature, many names ending in -idene indicate a fragment connected to the rest of a molecule by a carbon–carbon double bond. The fragment is conceptually formed by removing two hydrogens from a parent hydrocarbon, creating a site with two valences arranged in a double bond to the parent.

Notable examples include methylidene, which corresponds to the =CH2 group, and benzylidene, corresponding to a =CH–Ph fragment. Other idene groups are used in various contexts across organic and organometallic chemistry, and the exact structure can vary depending on what the idene is bonded to on the other end of the double bond.

In organometallic chemistry, idene groups frequently appear as alkylidene ligands, where a metal is bonded by a double bond to a carbon atom (for example M=CR2). Such ligands are central to several catalytic systems, including olefin metathesis catalysts. The term idene thus encompasses both simple substituent fragments within organic frameworks and more complex metal–carbon double-bond motifs.

The concept is distinct from related terms such as methylene (a saturated CH2 unit) and related sulfur, nitrogen, or oxygen analogs. It is used primarily as a naming convention to indicate a double-bonded, two-valence fragment attached to a parent structure.