Journal
ACTA CRYSTALLOGRAPHICA SECTION C-STRUCTURAL CHEMISTRY
Volume 72, Issue -, Pages 566-+Publisher
INT UNION CRYSTALLOGRAPHY
DOI: 10.1107/S2053229616009591
Keywords
2-nitrobenzoic acid; conformation; polymorphism; potential energy surface; crystal structure; disappearing polymorph; computational chemistry
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Funding
- Uzbek-German project [01DK14002]
- Chinese Scholarship Council
- North Rhine-Westphalia
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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, C7H5NO4, 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 center dot center dot center dot 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 center dot center dot center dot O contacts.
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