Trimethyl

Trimethyl is a term used in organic chemistry to describe a substituent or compound bearing three methyl groups (CH3). It functions as a prefix in systematic names to indicate three methyl substituents attached to a central atom or to the parent framework. The presence of three methyl groups increases steric bulk and hydrophobic character compared with fewer methyl groups.

In nomenclature, trimethyl appears in both substituent descriptions and full compound names. Examples include trimethylamine, where three methyl groups are bonded to a nitrogen atom (N(CH3)3); and 1,3,5-trimethylbenzene (mesitylene), where three methyl groups occupy distinct positions on a benzene ring. Trimethyl also describes groups such as the trimethylsilyl group, Si(CH3)3, which is widely used in organic synthesis to protect reactive sites or to modify reactivity. Other trimethyl-containing compounds include trimethyl phosphate, (CH3O)3P, and trimethyl borate, B(OCH3)3, each defined by three methoxy groups bound to a central atom.

Properties and considerations vary with the overall structure, but trimethyl substituents generally contribute to increased volatility in small molecules and heightened steric hindrance around the attachment point. They influence physical properties such as boiling points and solubility, and they can affect chemical reactivity and selectivity in synthesis.

See also dimethyl, trimethylsilyl, and tetramethyl for related alkyl-substitution patterns.