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Conformational dimorphism in o ‐nitrobenzoic acid: alternative ways to avoid the O…O clash
Author(s) -
Ibragimov Aziz,
Ashurov Jamshid,
Ibragimov Bakhtiyar,
Wang Ai,
Mouhib Halima,
Englert Ulli
Publication year - 2016
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s2053229616009591
Subject(s) - steric effects , intramolecular force , substituent , chemistry , intermolecular force , carboxylic acid , molecule , crystallography , hydrogen bond , crystal structure prediction , nitro , crystal structure , dihedral angle , benzene , stereochemistry , lattice energy , alkyl , organic chemistry
Polymorphism is a challenging phenomenon and the competitive packing alternatives which are characteristic for polymorphs may be encountered for essentially rigid molecules. A second crystal form of the well known compound o ‐nitrobenzoic acid, C 7 H 5 NO 4 , an important intermediate in the production of dyes, pharmaceuticals and agrochemicals, is described. Although obtained serendipitously, its intra‐ and intermolecular features match expectations from database searches and theoretical calculations. O—H…O hydrogen‐bonded carboxylic acid dimers represent the building blocks in both polymorphs. For steric reasons and in agreement with a calculated potential energy surface, the carboxylic acid and nitro groups cannot simultaneously be coplanar with the benzene ring but have to tilt. In the well established crystal form, this out‐of‐plane torsion is more pronounced for the nitro substituent. In contrast, the new polymorph is characterized by a major tilt of the carboxylic acid group. The molecules in both alternative crystal forms achieve a similar compromise with respect to acceptable intramolecular O…O contacts.