1,2-Diphenyl-2-(m-tolylamino)ethanone1

The title compound, C21H19NO, belongs to the family of α-aminoketones. The structure contains three benzene rings, two of which [the phenyl ring in the 1-position (B) and the methylaniline ring (A)] are nearly coplanar [dihedral angle = 5.4 (1)°], whereas the phenyl ring in the 2-position (C) is nearly normal to them [dihedral angles = 81.8 (1) and 87.0 (1)° for A/C and B/C, respectively]. The conformation of the N—H bond is syn to the C=O bond, favouring the formation of a centrosymmetric dimer of molecules in the crystal structure. The molecular packing is consolidated by this N—H⋯O hydrogen-bonding network.

The title compound, C 21 H 19 NO, belongs to the family ofaminoketones. The structure contains three benzene rings, two of which [the phenyl ring in the 1-position (B) and the methylaniline ring (A)] are nearly coplanar [dihedral angle = 5.4 (1) ], whereas the phenyl ring in the 2-position (C) is nearly normal to them [dihedral angles = 81.8 (1) and 87.0 (1) for A/C and B/C, respectively]. The conformation of the N-H bond is syn to the C O bond, favouring the formation of a centrosymmetric dimer of molecules in the crystal structure. The molecular packing is consolidated by this N-HÁ Á ÁO hydrogen-bonding network.
These compounds can be used as intermediates to synthesize other biologically active compounds like thiosemicarbazones.
Alpha-aminoketones also exhibit biological activity but are less active than the thiosemicarbazones. They are generally synthesised by the reaction of an alpha-hydroxiketone with an amine.
The molecular structure of the title molecule is illustrated in Fig. 1. According to the dihedral angles between the benzene rings planes, two benzene rings are nearly coplanar whereas the central ring is almost normal to them (5.3 (1)° for A/B, 81.8 (1)° for A/C and 87.0 (1)° for B/C). Comparing these values with those in the similar structure where the methyl subtitutent is in the para position (5.1° for A/B, 86.28° for A/C and 84.19° for B/C), there are no noticeable differences (Au & Tafeenko, 1986).
In the crystal structure, the molecular packing is made up of a network of weak hydrogen-bonding interactions ( Fig. 2 & Table 1), favouring the formation of centrosymmetric dimers. Such conformations bring the C═O and N-H bonds into a syn orientation. The intermolecular distance between the centroids of the parallel benzene rings is ca. 3.77 Å. This value suggests the absence of any relevant π-stacking interactions.
Experimental 0.0235 mol benzoin, 0.0235 mol 3-methylaniline and 0.0235 mol boric acid were added to 10 ml of ethyleneglycol. The mixture was heated to reflux for 1 h, then 15 ml of ethanol were added and the mixture cooled to RT. The reaction was followed using TLC. The yellow precipitate obtained was washed with cold water and ethanol (yield 85%). Yellow needle-like crystals, suitable for x-ray diffraction analysis, were obtained after a week by slow evaporation of a solution in ethanol.

Refinement
The NH H-atom was located in difference electron-density map and was freely refined: N-H = 0.858 (17) Å. The C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.98 Å, 0.93 Å and 0.96 Å for tertiary CH, aromatic CH and CH 3 H-atoms, respectively, with U iso (H) = k × U eq (C), where k = 1.2 for CH H-atoms, and 1.5 for CH 3 H-atoms.   Table 1 for details).

Special details
Experimental. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.