- A white crystalline phenol, C<sub>6</sub>H<sub>6</sub>O<sub>2</sub>, used as an antioxidant, photographic developer, stabilizer, and reagent.
- A divalent phenol (C<sub>6</sub>H<sub>4</sub> (OH)<sub>2</sub>) prepared by the oxidation of aniline and treatment of the quinol formed with sulphurous acid.
- A white crystalline substance, C6H4(OH)2, obtained by the reduction of quinone. It is a diacid phenol, resembling, and metameric with, pyrocatechin and resorcin. Called also <altname>dihydroxy benzene</altname>.
- The <xref>diphenol</xref> para-dihydroxy benzene, used as a mild <xref>reducing agent</xref> in <xref>photographic</xref> <xref>developing</xref>; <xref>isomeric</xref> with <xref>catechol</xref> and <xref>resorcinol</xref>.