Conformational dimorphism ino-nitrobenzoic acid: alternative ways to avoid the O...O clash

Abstract

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...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.

Soil fertility in agriculture: Main tasks

“…According to experimental data, the yield of cotton was 10.8 c/ha when planted without fertilizers and 33.0 c/ha when planted with permanent fertilizers. The same amount of fertilizers + mineral fertilizers + 30 tons/manure was applied at a yield of 40.2 centners/ha, or 7.2 centners/ha due to manure, this will be our study [7,8,9].…”

Two polymorphs of 2,5-dichloro-3,6-bis(dibenzylamino)-p-hydroquinone with flexible dibenzylamino groups

“…Polymorphism has attracted significant interest from both academic and industrial researchers in fields such as pharmaceuticals, foods and pigments, because the differences in the packing arrangements and molecular conformations of polymorphs result in different physicochemical properties in the crystalline state (Bernstein, 1987(Bernstein, , 2002. Therefore, the understanding and prediction of the occurrence of polymorphs has been intensively studied, particularly focusing on molecular structure (Chrobak et al, 2014;Sridhar et al, 2015;Ibragimov et al, 2016). Several structural parameters, such as hydrogen bonding and molecular flexibility, have been suggested as significant factors for polymorphism in molecular crystals (Yu et al, 2000).…”