trisubstituted

Trisubstituted is an adjective used in chemistry to describe a site or bond that bears three substituent groups. Substituent groups are atoms or groups other than hydrogen that replace hydrogens on a parent framework. The term is used to describe substitution patterns at carbon atoms, alkenes, and other reactive centers.

In alkenes, trisubstituted refers to the double bond having three non-hydrogen substituents attached to its two carbons. This pattern, which includes tetrasubstituted as four and disubstituted as two, influences steric hindrance, stability, and reactivity. An example is a vinyl unit where left carbon carries a methyl substituent and the right carbon carries a methyl and an ethyl substituent.

In carbocations, a tertiary (trisubstituted) carbocation is one where the positively charged carbon is bonded to three carbon substituents. Tertiary cations are typically more stable than primary or secondary due to hyperconjugation and inductive effects.

Counting substituents is context-dependent and usually excludes hydrogen unless stated. The term can also describe other centers with three substituents or ring systems bearing three attached groups. Trisubstitution is a common descriptor in reaction mechanisms, spectroscopy, and nomenclature.