Conformation of hydrogen‐bonded dimeric o‐methyl‐substituted benzoic acids

Molecules of 2,4‐dimethylbenzoic acid, C₉H₁₀O₂, form typical centrosymmetric hydrogen‐bonded dimers. The carboxyl group is twisted with respect to the benzene ring and the methyl group in the ortho position shows evasive in‐plane splaying. The relation between the in‐plane splaying and the twist angle of the carboxyl group for various ortho‐substituted dimeric derivatives of benzoic acid is presented. It shows how the steric strains are released depending on the numbers and positions of the substituents.