Molecules of 2,4-dimethylbenzoic acid, C(9)H(10)O(2), 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.