Intermolecularly Associated Carboxylic Acid Dimers in the Supramolecular Assembly of (R)-1,4-Benzodioxane 2-Carboxylic Acid

The title compound, C9H8O4, (I), crystallizes in the monoclinic space group P 21/c with unit cell parameters a = 7.3380(5) Å, b = 9.3790(7) Å, c = 12.3172(9) Å, β = 90.687(7)°, Z = 4. The molecule consists of a benzene ring fused to a 1,4 dioxane ring in a half-chair conformation with a carboxylic acid group bonded at the dioxane 2-position. The carboxylic acid group forms a classic O–H···O hydrogen bonded dimer with an O···O distance of 2.6292(12) Å in a R 2 2 (8) graph-set motif which links the molecules into pairs around inversion centers in a supramolecular assembly in the unit cell. The dihedral angle between the mean planes of the R 2 2 (8) graph-set motif’s of two adjacent dimers in the unit cell is 75.7(5)°. The mean plane of an R 2 2 (8) graph-set motif makes an angle of 88.4(5)° with the mean plane of the benzene ring in the same dimer and 13.1(2)° or 13.4(7)° with the mean plane of a benzene ring from an adjacent dimer. Additional weak Cg π-ring intermolecular interactions significantly influence the bond distances, bond angles and torsion angles of the dioxane ring and attached carboxyl group. Comparison to a MOPAC AM1computational calculation provides support to these observations. The association of carboxylic acid dimers in the supramolecular assembly of (R)-1,4-benzodioxane 2-carboxylic acid is investigated by examination of its crystal structure. Its geometric and packing parameters are described and compared to a MOPAC AM1 computational calculation.