2-Naphthoic acid at 153 K.

The structure of 2-naphthoic acid, C11H8O2, has been investigated at 153 K in order to determine the degree of disorder of the carboxylic acid group for comparison with that of the room-temperature structure. Analysis of the anisotropic displacement ellipsoids of the carboxyl-O atoms demonstrated that these parameters are wholly consistent with thermal motion of the O atoms. A model with ordered carboxyl-O atoms, but with the acid-H atom refined at two sites with 0.5 occupancy at each, was found to be statistically significantly better than a model with ordered carboxyl-O atoms and an ordered acid-H atom. Thus, as in the room-temperature study, the best structural description is that the O atoms are ordered and the acid-H atom is disordered. Nonetheless, comparisons of the geometric parameters of the carboxyl groups at 296 and 153 K suggest progress toward a fully ordered structure at the lower temperature. Except for the expected slight overall contraction and the slightly altered geometry of the carboxyl group, the structure is virtually the same as at room temperature.