1952REGULAR STRUCTURAL PAPERS will be published elsewhere in due course.) The 4,6-dilithio derivative of dibenzofuran, obtained from the reaction of dibenzoflwan with three equivalents of sec-butyllithium, was treated with dimethylformamide to afford dibenzofuran-4,6-dicarboxaldehyde. The Wittig-type reaction of this dialdehyde with diethylbenzylphosphonate and tBuOK in dry dimethylformamide gave 4,6-(2,2-diphenylethenyl)dibenzofuran in good yield. This stilbenoid was converted to the desired diphenanthro- m.p. 583-587 K (dec.)] by irradiation with UV fight in the presence of air and iodine. The diphenanthroflLran was crystallized from solution in dimethoxyethane to provide the experimental sample. The sample was mounted on a quartz pin with epoxy cement and a unit cell was determined at room temperature (295 K). The following non-idealized parameters were obtained from a leastsquares fitting of the setting angles for 25 centered reflections: a = 6.825 (2), b --34.842 (4), c = 7.749 (1) A,, oL = 90.01 (2), = 90.01 (2), 3' = 90.01 (2) °, V = 1842.8 (6) A. 3. The crystal was then cooled to 191 K utilizing a Molecular Structure Corporation low-temperature apparatus. The stated temperature was measured continuously during data collection in the cold gas flow just upstream of the crystal; the estimated uncertainty of the crystal temperature is -t-2 K. Unit-cell parameters for the lowtemperature cell were obtained from a symmetry-constrained least-squares fit of the same reflections used to determine the room-temperature cell. The low-temperature unit-cell parameters are given in the Experimental section.Data were collected utilizing graphite-monochromated radiation. Scan widths were (1.4 + 0.35tan0) ° in w, with a background/scan time ratio of 1:2. No corrections were made for decay or absorption; the data were corrected for Lorentz and polarization effects. Systematic absences (Okl, k+l = odd; hk0, h = odd) were consistent with two space groups: Pnma and Pna21. Since intensity statistics indicated a centrosymmetric space group, Pnma (No. 62) was given initial preference; refinement proceeded well and it was adopted.The direct-met,hods program SHELXS86 was used to generate an E map from which the initial positions of the non-H atoms were identified. Fourier difference methods were then used to locate the H atoms. The C and O atoms were refined anisotropically and the H atoms isotropically using full-matrix least squares (TEXSAN; Molecular Structure Corporation, 1989). The weighting scheme used was w = o. Cryst. CA9, 398-400. Gerkin, R. E., . ActaCryst. C40, 1892-1894. Gerkin, R. E. & Reppart, W. J. (1985. Acta Cryst. C41, 961-963. Gerkin, R. E. & Reppart, W. J. (1986). Acta Cryst. C42, 480-482. Johnson, C. K. (1976). ORTEPII. Ridge National Laboratory, Tennessee, USA. Kay, M. I., Okaya, Y. & Cox, D. E. (1971). Acta Cryst. B27, 26-33. Molecular Structure Corporation (1989 Acta Cryst. (1993). C49, 1952-1958 Redetermination of the Structures of 1-Naphthoic Acid and 2-Naphthoic Acid AbstractThe structures of 1...

(5)A] indicate almost complete disorder of the H atoms of these groups. Hydrogen bonding occurs in cyclic dimer fashion between two molecules related by a center of inversion. The carboxyl hydrogens appear to be subject to a symmetric doubleminimum potential and to be disordered via tunneling: there is no evidence that the carboxyl oxygens are disordered. The mean carboxyl H--O acceptor distance is 1-90 (7) A.

Anthracene-9-carboxylic acid, C15H10O2, was found to crystallize in the centrosymmetric space group P2(1)/n. The hydrogen bonding is of the cyclic-dimer type about a center of symmetry. The carboxyl O atoms are ordered, as is the carboxyl H atom. The anthracene core is almost planar and shows good agreement with the anthracene core of anthracene-1, 8-dicarboxylic acid. The carboxyl group plane makes a dihedral angle of 54.87 (6) degrees with the best-fit anthracene core plane.

No abstract

The title compound, C15H10O2, was found to crystallize in the centrosymmetric space group P2(1)/n. The hydrogen bonding is of the cyclic dimer type about a center of symmetry. The carboxyl O atoms are ordered as is the carboxyl H atom. The anthracene core, while less nearly planar, shows good agreement with the anthracene cores of anthracene-9-carboxylic acid and anthracene-1,6-dicarboxylic acid. The carboxyl group plane makes a dihedral angle of 12.4 (2) degrees with the best-fit anthracene core plane.