Metahydroxy

Metahydroxy is a descriptor used in organic chemistry to denote a hydroxyl (-OH) substituent on an aromatic ring that occupies the meta position relative to another reference substituent. On a benzene ring with a substituent at position 1, a hydroxy group at position 3 is referred to as meta-hydroxy, and the compound is often described as a 3-hydroxy derivative.

Common examples include m-hydroxybenzaldehyde (3-hydroxybenzaldehyde) and m-hydroxybenzoic acid (3-hydroxybenzoic acid). These isomers differ from their ortho- and para-hydroxy counterparts in relative position on the ring, which can influence physical properties such as melting point, polarity, and acidity, as well as reactivity in further chemical transformations.

Metahydroxy derivatives occur in natural products and synthetic compounds used in pharmaceuticals, dyes, and polymers. The position of the hydroxyl group can affect hydrogen bonding patterns, intramolecular interactions, and the molecule’s overall chemical behavior, including acidity of the phenolic OH and its participation in subsequent reactions.

Synthesis of meta-hydroxy derivatives often requires strategies that direct or install the hydroxyl group at the meta position. This can involve using meta-directing groups, or employing late-stage functionalization and other specialized methods to achieve meta-hydroxylation after the ring has been put in place with the desired substituents.

See also: ortho-hydroxy, para-hydroxy, hydroxy group, phenol, benzoic acid.