REDETERMINATION OF THE STRUCTURES OF 1-NAPHTHOIC ACID AND 2-NAPHTHOIC ACID

The structures of 1-naphthoic acid and 2-naphthoic acid have been investigated in order to determine the degree of disorder of the carboxylic acid groups. 1-Naphthoic acid was found to be completely ordered with C-O bond lengths of 1.214(3) and 1.312 (3) Angstrom, and C-C-O bond angles of 124.8 (2) and 114.2(2)Angstrom. 2-Naphthoic acid was found to possess a significant degree of disorder with C-O bond lengths of 1.256(3) and 1.274(3) Angstrom, and C-C-O bond angles of 117.7 (2) and 119.1 (2)Angstrom. In 2-naphthoic acid, the acid H atom was refined at two sites with 0.5 occupancy at each. Analysis of the anisotropic displacement ellipsoids of the acid O atoms for each structure demonstrated that these parameters are consistent with thermal motion of the O atoms. These results indicated that the proton, but not the O atoms, is disordered in the carboxylic acid group of 2-naphthoic acid. In each structure, the acid molecules form cyclic dimers about inversion centers, with an O...O(acceptor) distance of 2.653(3) in 1-naphthoic acid and 2.618 (3) Angstrom in 2-naphthoic acid. The cyclic dimers form layers in each of these structures wherein lateral closest intermolecular approaches to the acid O atoms are from ring H atoms. The intermolecular O...H close approaches, together with the intramolecular close approaches, are very uniform in distance and angle of approach for the two O atoms in the 2-naphthoic acid structure. In 1-naphthoic acid, the corresponding approaches are much less uniform due primarily to the presence of an H atom in a position peri to the carboxylic acid group. The layers are stacked in notably different arrangements which, however, conform closely to two categories of arrangement developed originally to describe the structures of benzoic acids.