On December 1, 2020, Guillen, Marilia; Mora, Asiloe J.; Belandria, Lusbely M.; Seijas, Luis E.; Ramirez, Jeans W.; Burgos, Jose L.; Rincon, Luis; Delgado, Gerzon E. published an article.Formula: C10H11NO3 The title of the article was Two conformational polymorphs of 4-methylhippuric acid. And the article contained the following:
4-Methylhippuric acid {systematic name: 2-[(4-methylbenzoyl)amino]ethanoic acid}, a p-xylene excreted metabolite with a backbone containing three rotatable bonds (R-bonds), is likely to produce more than one stable mol. structure in the solid state. In this work, we prepared polymorph I by slow solvent evaporation (plates with Z’ = 1) and polymorph II by mech. grinding (plates with Z’ = 2). Potential energy surface (PES) anal., rotating the mol. about the C-C-N-C torsion angle, shows four conformational energy basins. The second basin, with torsion angles near -73°, agree with the conformations adopted by polymorph I and mols. A of polymorph II, and the third basin at 57° matched mols. B of polymorph II. The energy barrier between these basins is 27.5 kJ mol-1. Superposition of the mols. of polymorphs I and II rendered a maximum r.m.s. deviation of 0.398 Å. Polymorphs I and II are therefore true conformational polymorphs. The crystal packing of polymorph I consists of C(5) chains linked by N-H···O interactions along the a axis and C(7) chains linked by O-H···O interactions along the b axis. In polymorph II, two mols. (A with A or B with B) are connected by two acid-amide O-H···O interactions rendering R22(14) centrosym. dimers. These dimers alternate to pile up along the b axis linked by N-H···O interactions. A Hirshfeld surface anal. localized weaker noncovalent interactions, C-H···O and C-H···π, with contact distances close to the sum of the van der Waals radii. Electron d. at a local level using the Quantum Theory of Atoms in Mols. (QTAIM) and the Electron Localization Function (ELF), or a semi-local level using noncovalent interactions, was used to rank interactions. Strong closed shell interactions in classical O-H···O and N-H···O hydrogen bonds have electron d. highly localized on bond critical points. Weaker delocalized electron d. is seen around the p-methylphenyl rings associated with dispersive C-H···π and H···H interactions. The experimental process involved the reaction of 2-(4-Methylbenzamido)acetic acid(cas: 27115-50-0).Formula: C10H11NO3
The Article related to two conformational polymorph methylhippuric acid, dft calculations, hirshfeld surface analysis, qtaim and nci topological analysis, conformational polymorphism, hydrogen bonding, noncovalent interactions, single-crystal x-ray diffraction and other aspects.Formula: C10H11NO3
Referemce:
Amide – Wikipedia,
Amide – an overview | ScienceDirect Topics