2-Methyl-3-(4-methylphenyl)-5,6-diphenyl-2,3-dihydropyrazine

In the title molecule, C24H22N2, four atoms (N—C—C—N) of the heterocyclic ring, with their attached H atoms, and all atoms of the methyl group, are disordered over two positions; the site-occupancy factor of the major component is 0.713 (6). The major disorder component of the heterocyclic ring adopts a half-chair conformation, with all substituents equatorial. The benzene ring adjacent to the methyl group forms dihedral angles of 79.68 (11) and 80.92 (11)° with the phenyl rings; the dihedral angle between adjacent phenyl rings is 59.10 (11)°. The crystal structure features three C—H⋯π interactions.

In the title molecule, C 24 H 22 N 2 , four atoms (N-C-C-N) of the heterocyclic ring, with their attached H atoms, and all atoms of the methyl group, are disordered over two positions; the site-occupancy factor of the major component is 0.713 (6). The major disorder component of the heterocyclic ring adopts a half-chair conformation, with all substituents equatorial. The benzene ring adjacent to the methyl group forms dihedral angles of 79.68 (11) and 80.92 (11) with the phenyl rings; the dihedral angle between adjacent phenyl rings is 59.10 (11) . The crystal structure features three C-HÁ Á Á interactions.

Related literature
For the biological properties of dihydropyrazines and for closely related crystal structures, see: Anuradha et al. (2009Anuradha et al. ( , 2011 Table 1 Hydrogen-bond geometry (Å , ).

Comment
As part of our investigations of dihydropyrazine derivatives (Anuradha et al., 2009(Anuradha et al., , 2011 to compare their chemical and biological activities, we have undertaken the X-ray crystal structure analysis of the title compound. In the title molecule, C 24 H 22 N 2 , Fig.1., the heterocyclic ring with the major disorder component, adopts a half-chair conformation, with all substituents equatorial. The phenyl ring at C1 makes a dihedral angle of 59.10 (11) and 79.68 (11)° with the phenyl ring at C2 and benzene ring at C5A respectively. The dihedral angle between the phenyl ring at C2 and benzene ring at C5A is 80.92 (11)°. Four atoms (N2-C3-C5-N1) of the heterocyclic ring, with their attached H atoms, and all atoms of the methyl group, are disordered over two positions; the site occupancy factors refined to 0.713 (6) and 0.287 (6). The crystal structure is stabilized by three C-H···π interactions (Table 1). No hydrogen bonds are found in the crystal structure.

Experimental
To a homogeneous solution of benzil (1.05 g, 0.005 mol) and 1-methyl-2-(4′-methylphenyl)-ethanediaminedihydrochloride (1.29 g, 0.005 mol) in ethanol (20 ml), sodium acetate trihydrate (2.04 g, 0.015 mol) was added. The precipitated sodium chloride was filtered off and the filtrate was refluxed for 2 h. On completion of the reaction, as indicated by TLC, the reaction mixture was poured into crushed ice and the resulting solid was filtered and purified by column chromatography on silica gel. Elution with benzene-petroleum ether (4:1 v/v) at 333-353 K gave the pure product. Yield 1.60 g (72%). The pure product was recrystallized in ethyl acetate, to obtain crystals suitable for X-ray diffraction studies.

Refinement
The H atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.95-1.00 Å, and with U iso (H) = 1.2-1.5Ueq(C). Four atoms (N2/C3/C5/N1) of the heterocyclic ring, with their attached H atoms, and all atoms of the methyl group, are disordered over two positions. The anisotropic displacement parameters of equivalent atoms were constrained to be equal; the site occupancy factors refined to 0.713 (6) and 0.287 (6). A damping factor (damp 100 in the final refinement cycles) was applied to avoid large displacements of the disordered hydrogen atoms.  The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level. H atoms are shown as small spheres of arbitrary radius. Only the major disorder component is shown. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.71 e Å −3 Δρ min = −0.35 e Å −3 Special details 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 e.s.d.'s 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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (