Dihydroxybenzoic acid

Dihydroxybenzoic acids (DHBA) are a type of phenolic acids.

There are six main compounds, having all the same molecular formula C7H6O4. Those are:

2,3-Dihydroxybenzoic acid (2-Pyrocatechuic acid or hypogallic acid) 2,4-Dihydroxybenzoic acid (β-Resorcylic acid) 2,5-Dihydroxybenzoic acid (Gentisic acid) 2,6-Dihydroxybenzoic acid (γ-Resorcylic acid) 3,4-Dihydroxybenzoic acid (Protocatechuic acid) 3,5-Dihydroxybenzoic acid (α-Resorcylic acid)

Orsellinic acid is also a dihydoxybenzoic acid having an extra methyl group.