Glutaconic acid, also known as 2-pentenedioic acid, is an unsaturated dicarboxylic acid. It is formed as one of the degradation products during the partial wet oxidation (PWO) of alkali lignin. The analysis of its crystal structure indicates that the compound exists predominantly in the trans-conformation. The geometric bond lengths and bond angles of glutaconic acid have been obtained using Hartree–Fock (HF), density functional calculations and IR spectral data.