3substituted

3-substituted is a descriptor used in organic chemistry to indicate that a substituent is attached at the third position of a defined parent structure. The designation depends on a chosen reference point, such as a functional group or a particular atom in a ring or chain, and is applied to monocyclic and polycyclic systems as well as acyclic molecules where a clear numbering is possible. The term is most useful when the full structure is specified, because the same locant can mean different positions in different parent frameworks.

In nomenclature, position numbers are assigned to give the lowest possible locants under IUPAC rules. In aromatic rings, a substituent at position 3 relative to a reference at position 1 is often described as meta, so a 3-substituted benzene with a substituent at position 3 is related to the 1,3-disubstituted pattern. However, the plain label “3-substituted” by itself does not uniquely describe all substituent positions; the complete name must specify the parent and all substituents to avoid ambiguity.

Synthesis and planning for 3-substituted compounds rely on regioselectivity and the directing effects of existing substituents or ring chemistry. Meta-directing groups tend to bias reactions toward the 3-position on aromatic rings, while other substrates require alternative strategies to place a substituent at carbon 3.

Examples include 3-bromotoluene (methyl at position 1, bromine at 3) and 3-methoxytoluene. In nonaromatic rings, 3-substituted cycloalkanes such as 3-phenylcyclohexane illustrate the same locational concept, defined with respect to a chosen reference carbon.