Abstract
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 mol-ecular units as asymmetric units with no solvent in the unit cells. Crystal structure I, TFMP, is the result of the crystallization of N-[4-(tri-fluoro-meth-yl)phen-yl]benzamide, C14H10F3NO. Crystal structure II, MOP, is composed of N-(4-meth-oxy-phen-yl)benzamide, C14H13NO2, units. TFMP is triclinic, space group P , consisting of two mol-ecules in the unit cell related by the center of symmetry. MOP is monoclinic, space group P21/c, consisting of four mol-ecules in the unit cell. Both types of mol-ecules 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. Inter-molecular inter-actions were examined by Hirshfeld surface analysis and qu-anti-fied by calculating mol-ecular inter-action energies. The results of this study demonstrate that both hydrogen bonding and dispersion are essential to the side-by-side stacking of mol-ecular units in these crystal structures. Weaker dispersion inter-actions along the axial directions of the mol-ecules reveal insight into the melting mechanisms of these crystals.
Highlights
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
TFMP is triclinic, space group P1, 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 parasubstituted phenyl ring. The orientations of these planar regions within the asymmetric units are compared to their predicted orientations, in isolation, from density functional theory (DFT) calculations
Summary
Numerous methodologies have been developed to form amide C—N bonds due to their prevalence in biomolecules, such as peptides and proteins, and in synthetic targets (Seward & Jakubke, 2002; Greenberg et al, 2000). Aryl amides can be found in a variety of pharmaceutical drugs and in polymers such as KevlarTM (Masse et al, 1998; Evano et al, 2004, 2008; Satyanarayana et al, 2007; Tanner et al, 1989). A series of aryl amides were synthesized and isolated during the development of a copper-mediated concurrent tandem catalytic methodology for the amidation of aryl chlorides (Chang et al, 2019). The crystal structures of two of these aryl amides, derived from the cross-coupling of either 4-chlorobenzotrifluoride or 4-chloroanisole with benzamide, are reported here
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