12disubstituted

12disubstituted is usually encountered as an informal or typographical variant of 1,2-disubstituted, describing a molecule that bears two substituent groups located at adjacent positions on a parent framework. The standard nomenclature uses numerals with a comma, for example 1,2-disubstituted, to specify the two positions. In practice, the concept applies across different structural motifs, including arenes, cycloalkanes, and polycyclic systems.

In aromatic chemistry, a 1,2-disubstituted benzene derivative is often referred to as ortho-disubstituted, with the two substituents at adjacent carbon atoms on the ring. The specific identity of the substituents and their relative orientation influence reactivity, directing effects, and physical properties. In cycloalkanes, 1,2-disubstitution denotes adjacent substituents on the ring, and the stereochemistry can be described as cis-1,2- or trans-1,2-, depending on whether the substituents lie on the same or opposite faces of the ring.

Common examples include 1,2-dichlorobenzene, 1,2-dimethylcyclohexane, and cis-1,2-dimethylbenzene. The descriptor is also relevant in synthesis and mechanism discussions, where the position pattern (1,2-) affects regioselectivity and subsequent transformations. When more distant positions are involved, other locants such as 1,3- or 1,4- are used, following IUPAC rules to minimize the locant set.

To avoid ambiguity, most modern literature uses 1,2-disubstituted rather than the concatenated form 12disubstituted. If encountered, verify the intended locant pattern and nomenclature in the source.