Conformational Switch of Benzanilide Derivative Induced by Acid; Effect of Pentafluorobenzoyl Group

Amide-based molecular switches had its limitation on structural diversities. In this work, we designed and synthesized a series of pentafluorobenzoyl-based benzanilide compounds. The conformational ratio of these compounds in solution was correlated linearly with Hammett's σ_p value of the substituent on the anilide ring, reflecting the repulsive interaction between the carbonyl group and the electron-rich aryl group. The addition of acid into the solution of 6, bearing pentafluorobenzoyl group, switched the stable amide conformation. In addition, the sizeable rotational barrier of 6 induced by the pentafluorobenzoyl moiety enabled us to monitor the conformational transition by means of ¹H NMR spectroscopy.

Crystal structures of N-[4-(trifluoromethyl)phenyl]benzamide and N-(4-methoxyphenyl)benzamide at 173 K: a study of the energetics of conformational changes due to crystal packing

The conformations of two aryl amides have been determined experimentally in crystal structures using X-ray data and calculated with DFT methods for the isolated mol­ecules. Geometrical comparisons are made along with energy analyses of the inter­molecular inter­actions in the two crystal structures.

As a part of our study of the syntheses of aryl amides, the crystal structures of two benzamides were determined from single-crystal X-ray data at 173 K. Both crystal structures contain mol­ecular units as asymmetric units with no solvent in the unit cells. Crystal structure I, TFMP, is the result of the crystallization of N-[4-(tri­fluoro­meth­yl)phen­yl]benzamide, C₁₄H₁₀F₃NO. Crystal structure II, MOP, is composed of N-(4-meth­oxy­phen­yl)benzamide, C₁₄H₁₃NO₂, units. TFMP is triclinic, space group P, consisting of two mol­ecules in the unit cell related by the center of symmetry. MOP is monoclinic, space group P2₁/c, consisting of four mol­ecules in the unit cell. Both types of mol­ecules contain three planar regions; a phenyl ring, an amide planar region, and a para-substituted phenyl ring. The orientations of these planar regions within the asymmetric units are compared to their predicted orientations, in isolation, from DFT calculations. The aryl rings are tilted approximately 60° with respect to each other in both experimentally determined structures, as compared to 30° in the DFT results. These conformational changes result in more favorable environments for N—H⋯O hydrogen bonding and aryl ring π-stacking in the crystal structures. Inter­molecular inter­actions were examined by Hirshfeld surface analysis and qu­anti­fied by calculating mol­ecular inter­action energies. The results of this study demonstrate that both hydrogen bonding and dispersion are essential to the side-by-side stacking of mol­ecular units in these crystal structures. Weaker dispersion inter­actions along the axial directions of the mol­ecules reveal insight into the melting mechanisms of these crystals.

Effect of Hydrogen Bonds and π...π-interactions on the Crystallization of Phenyl-perfluorophenyl Amides: Understanding the Self-organization of a Cocrystal

A series of N-arylbenzamides containing amide group and phenyl−perfluorinated rings were used as the smallest molecules to investigate the direct influence of hydrogen bond and aromatic donor-acceptor complementarity in the...

Supramolecular Packing of a Series of N-Phenylamides and the Role of NH···O=C Interactions

A series of seven N-phenylamides [R-C(O)NHPh, in which R: CH₃, C(CH₃)₃, Ph, CF₃, CCl₃, CBr₃, and H] were used as models in this study. Molecular packing and intermolecular interactions were evaluated by theoretical calculations, solution NMR, and quantum theory of atoms in molecules analyses. Crystallization mechanisms were proposed based on the energetic and topological parameters using the supramolecular cluster as demarcation. Concentration-dependent ¹H NMR experiments corroborated the proposed interactions between molecules. For all compounds (except for R: H, which initially formed tetramers), layers (two-dimensional) or chains (one-dimensional) were formed in the first stage of the proposed crystallization mechanisms. The presence of strong intermolecular NH···O=C interactions promoted the first stages. The study in solution provided different values of association constant (K _ass) governed by the hydrogen bond NH···O=C, showing that the stronger interactions are directly influenced by the substituent steric hindrance. A correlation between K _{ass(NH···O=C)} from the solution and the NH···O=C interaction energy in the crystal showed a good trend.

Raman spectra of crystalline secondary amides

We present a Raman-spectroscopic study of secondary amides (acetanilide, methacetin, phenacetine, orthorhombic and monoclinic polymorphs of paracetamol) as well as simple amides formanilide and benzanilide. The study was carried out on single crystals and in the temperature range of 5-300K. The series of compounds with the same molecular fragment - acetamide group - can serve as a model system to study the interrelation between this group and the properties of the intermolecular "peptide-type" NH⋯OC hydrogen bonds. For all of the "acetamide family" of the compounds, similar changes in the Raman spectra were observed upon cooling of the samples: emergence of new Amide I(-) and Amide I(+) bands, which are red and blue shifted, respectively, from the conventional Amide-I band by around of 5-10cm^-1. Corresponding changes in the same temperature range were observed for the NH out-of-plane bending (Amide V) and NH stretching vibrations of the NH⋯OC hydrogen bond. All of the spectral changes observed upon cooling of the samples can be presumed to result from a delocalization of the Amide-I and NH modes and appearance of dynamical (Davydov's) splitting at low temperature.