isomersortho

Isomersortho is a term used in organic chemistry to denote the ortho isomer of a substituted benzene. In the context of disubstituted benzenes, the ortho isomer has two substituents in adjacent positions on the ring, specifically at the 1 and 2 positions. The designation comes from the prefixes ortho-, meta-, and para-, which describe relative substituent locations around the benzene ring: ortho corresponds to 1,2-, meta to 1,3-, and para to 1,4-. Examples include o-xylene (1,2-dimethylbenzene), o-nitrotoluene (1-methyl-2-nitrobenzene), and o-dichlorobenzene (1,2-dichlorobenzene).

Naming conventions for ortho isomers are used to distinguish them from their meta and para counterparts, which can exhibit markedly different physical and chemical properties despite sharing the same molecular formula. Properties such as boiling and melting points, reactivity in electrophilic aromatic substitution, and dipole moments can vary among ortho, meta, and para isomers due to differences in steric hindrance, symmetry, and intermolecular interactions. In many cases, ortho isomers show different crystallization behavior and may have higher or lower affinities for solvents compared with their meta or para analogs.

Analytical methods often reveal distinct signatures for ortho isomers. Nuclear magnetic resonance (NMR) spectroscopy, for instance, typically shows characteristic patterns and coupling constants for adjacent (ortho) protons, which differ from those observed in meta or para substitutions. Chromatographic separation can also exploit the subtle differences in polarity and steric bulk among the isomers.

See also: isomer, benzene, ortho, meta, para.