Crystal structure of 2,4,6-tri-methyl-benzoic anhydride

Abstract

The title compound, C₂₀H₂₂O₃, was formed in the reaction between 2,4,6-tri-methyl-benzoic acid and N,N-diiso-propyl-ethyl-amine in the presence of 1,3-di-chloro-1,3-bis-(di-methyl-amino)-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 mol-ecule, 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-tri-methyl-phenyl 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, mol-ecules are linked by weak C-H⋯O hydrogen bonds and C-H⋯π inter-actions. The packing features wavy chains that extend parallel to [001].

Keywords: 2,4,6-tri­methyl­benzoic anhydride; crystal structure; mesitoic anhydride.

Figure 1

The mol­ecular structure of the title compound. Only half of the mol­ecule is crystallographically unique (labelled atoms). Displacement ellipsoids are drawn at the 50% probability level.

Figure 2

Packing diagram of the title compound, viewed in projection down [100], showing wavy [001] chains.

Figure 3

Short inter­molecular contacts (defined in the text and close to the sum of the van der Waals radii; shown as heavy dotted lines), with only donors from the central mol­ecule included (Table 1 ▸).