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) A, and C--C--O bond angles of 124.8 (2) and 114.2 (2) degrees. 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) A, and C--C--O bond angles of 117.7 (2) and 119.1 (2) degrees. 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) A 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.(ABSTRACT TRUNCATED AT 250 WORDS)