4methyl

4-methyl is a locant used in chemical nomenclature to indicate a methyl substituent attached to the fourth carbon of a parent molecule. It is employed in systematic IUPAC names for a wide range of compounds, including monocyclic rings such as 4-methylcyclohexane and benzene derivatives. The 4-position designation specifies the position of the methyl group on the ring or chain, and it helps distinguish isomers that differ only by where the methyl group is attached.

In the context of benzene rings with multiple substituents, the 4-position is para to a reference substituent at position 1. When naming such compounds, the lowest set of locants is sought, and the para relationship is often conveyed more succinctly with the prefix para- (p-), though 4-methyl remains the explicit systematic locant in full IUPAC names. This usage supports precise communication about molecular structure in chemical literature and databases.

Examples include 4-methylcyclohexane, where a methyl group occupies the fourth carbon of a cyclohexane ring; 4-methylbenzaldehyde (commonly known as p-tolualdehyde), which has a formyl group and a methyl group para to each other on a benzene ring; 4-methylphenol (p-cresol), and 4-methylbenzenamine (p-toluidine). The term is primarily a descriptive feature of naming rather than a distinct functional class, and it appears in many organic compounds to specify methyl substitution at the para position relative to other substituents.