orthohydroxy

Ortho-hydroxy, often written as orthohydroxy or o-hydroxy, is a descriptive term used in organic chemistry to indicate a hydroxy substituent positioned at the ortho location on a benzene ring relative to another substituent. The prefix “ortho-” denotes adjacent (1,2-) substitution on the ring, and the hydroxy group is the functional group –OH.

In systematic naming, the hydroxy group is common in phenolic compounds, and the 2-position (ortho) is specified with a numeral. For example, 2-hydroxybenzoic acid is salicylic acid, where the hydroxy group is ortho to the carboxyl group. Another example is 2-hydroxybenzaldehyde (salicylaldehyde). When a compound contains two hydroxy groups, the term can describe the relationship between them as in catechol, which is 1,2-dihydroxybenzene, i.e., two hydroxy groups in the ortho relationship to each other.

The concept is also used to describe substituent patterns in other aromatic systems, though “orthohydroxy” is most common in reference to benzene derivatives. The ortho arrangement can influence intramolecular interactions, such as hydrogen bonding between the hydroxy group and adjacent functional groups, and can affect acidity and reactivity compared with meta- and para- isomers.

Note that orthohydroxy is a descriptive descriptor rather than a standalone chemical name. In practice, it is used to convey the spatial relationship of a hydroxy group to another substituent on an aromatic ring. See also ortho-, hydroxy, phenol, and related positional terminology.