2-Ethyl-3,5,6-triphenylpyrazine

In the title molecule, C24H20N2, the pyrazine ring is significantly distorted from planarity, presumably due to steric crowding, and its conformation is well described as a flattened twist-boat. The benzene ring adjacent to the ethyl group forms dihedral angles of 53.79 (13) and 85.47 (12)° with the other benzene rings; the dihedral angle between adjacent benzene rings is 57.90 (12)°. The ethyl group is disordered over two positions; the site-occupancy factor of the major component is 0.546 (4). No hydrogen bonds are found in the crystal structure.

In the title molecule, C 24 H 20 N 2 , the pyrazine ring is significantly distorted from planarity, presumably due to steric crowding, and its conformation is well described as a flattened twist-boat. The benzene ring adjacent to the ethyl group forms dihedral angles of 53.79 (13) and 85.47 (12) with the other benzene rings; the dihedral angle between adjacent benzene rings is 57.90 (12) . The ethyl group is disordered over two positions; the site-occupancy factor of the major component is 0.546 (4). No hydrogen bonds are found in the crystal structure.

Comment
As part of our investigations of pyrazine derivatives (Anuradha et al., 2009) to compare their chemical and biological activities, we have undertaken the X-ray crystal structure analysis of the title compound.
In the title molecule, Fig.1, the pyrazine ring adopts a flattened twist-boat conformation. The phenyl ring at position 5 makes a dihedral angle of 53.79 (13)° and 57.90 (12)° with the phenyl rings at position 3 and 6 respectively. The dihedral angle between the phenyl rings at positions 3 and 6 is 85.47 (12)°. The ethyl group is found to be disordered over two positions; the site occupancy factors refined to 0.546 (4) and 0.454 (4). No classical hydrogen bonds are found in the crystal structure.

Experimental
To a homogeneous solution of benzil (1.05 g, 0.005 mol) and 1-ethyl-2-phenyl-1,2-ethanediaminedihydrochloride (1.45 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 (3:2 v/v) at 333-353 K gave the pure product. Yield 1.54 g (70%).
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 = 0.95-0.99 Å , and with U iso (H) = 1.2-1.5U eq (C). The ethyl group is found to be disordered over two positions. The anisotropic displacement parameters of equivalent atoms were constrained to be equal; the site occupancy factors refined to 0.546 (4) and 0.454 (4).

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as small spheres of arbitrary radius. Only the major disorder component of ethyl group is shown.

2-Ethyl-3,5,6-triphenylpyrazine
Crystal data C 24 H 20 N 2 M r = 336.42 Triclinic, P1 Hall symbol: -P 1 a = 9.2327 (9) Å b = 9.8708 (11) Å c = 10.6787 (14)  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.29 e Å −3 Δρ min = −0.21 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. (