Hydroxynaphthoquinone

A hydroxynaphthoquinone is any of several organic compounds that can be viewed as derivatives of a naphthoquinone through replacement of one hydrogen atom by a hydroxyl group.
In general, the term may mean any naphthoquinone derivative where any number n of hydrogens have been replaced by n hydroxyls, so that the formula is. In this case the number n is indicated by a multiplier prefix.
The unqualified term "hydroxynaphthoquinone" usually means a derivative of 1,4-naphthoquinone. Other hydroxy- compounds can be derived from other isomers of the latter, such as 1,2-naphthoquinone and 2,6-naphthoquinone. The IUPAC nomenclature uses dihydronaphthalenedione instead of "naphthoquinone", with the necessary prefixes to indicate the positions of the carbonyl oxygens — as in 5,8-dihydroxy-1a,8a-dihydronaphthalene-1,4-dione.
The hydroxynaphtoquinones include many biologically and industrially important compounds, and are a building-block of many medicinal drugs.

(Mono)hydroxynaphtoquinones

From 1,4-naphthoquinone

Due to its symmetry there are only three isomers:

2-Hydroxy-1,4-naphthoquinone, coloring principle of henna.
5-Hydroxy-1,4-naphthoquinone, coloring principle of black walnut. Also active antimicrobial principle in Caesalpinia sappan heartwood.
6-Hydroxy-1,4-naphthoquinone, can be prepared from 1,7-dihydroxynaphthalene. One of the main products of photochemical oxidation of 1-naphthol.

From 1,2-naphthoquinone

From 1,2-naphthoquinone there are 6 possible isomers:

From 2,3-naphthoquinone

From 2,3-naphthoquinone, also a symmetric molecule there are only three isomers:

From 2,6-naphthoquinone

From the symmetrical 2,6-naphthoquinone there are only three:

(Poly)hydroxynaphthoquinones