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Phenanthrene-4-carboxylic acid, C15H10O2, crystallized in the centrosymmetric space group P21/n, while 1,2-dihydrophenanthrene-4-carboxylic acid, C15H12O2, crystallized in the centrosymmetric space group Pbca. In each structure there is a single type of hydrogen bond: it is of the cyclic dimer type about a center of symmetry. The Odonor...Oacceptor distances are 2.634 (2) and 2.651 (2) Å and the O-H...O angles are 176 (3) and 173 (2) °, respectively, for the two structures. In each structure the carboxylic H atom and O atoms are ordered. The phenanthrene core of the fully aromatic acid is roughly planar; the dihedral angle between the best-fit core plane and the carboxy group plane is 63.7 (1)°. As expected, the hydrogenated ring of the second acid is much less nearly planar; the remaining naphthalenoid core is, however, roughly planar and the dihedral angle between this best-fit plane and the carboxy group plane is 60.4 (1)°.

Supporting information


Crystallographic Information File (CIF)
Contains datablocks global, 1, 2


Structure factor file (SHELXL table format)
Supplementary material


Structure factor file (SHELXL table format)
Supplementary material

CCDC references: 130150; 130151


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