Crystal structure of 2,4,6-tri­methyl­benzoic anhydride

The title compound, C(20)H(22)O(3), was formed in the reaction between 2,4,6-tri­methyl­benzoic acid and N,N-diiso­propyl­ethyl­amine in the presence of 1,3-di­chloro-1,3-bis­(di­methyl­amino)­propenium hydrogen dichloride, and was recrystallized from diethyl ether solution. It is the first exclusively alkyl-substituted benzoic anhydride to have been structurally characterized. The asymmetric unit consists of a half mol­ecule, the other half of which is generated by twofold rotation symmetry; the dihedral angle between the symmetry-related aromatic rings is 54.97 (3)°. The geometric parameters of the aromatic ring are typical of those for 2,4,6-tri­methyl­phenyl substituted groups. The C=O and C—O bond lengths are 1.1934 (12) and 1.3958 (11) Å, respectively, and the angle between these three atoms (O=C—O) is 121.24 (9)°. In the crystal, mol­ecules are linked by weak C—H⋯O hydrogen bonds and C—H⋯π inter­actions. The packing features wavy chains that extend parallel to [001].