(E)-2-Acetylpyrazine 4-nitrophenylhydrazone

In the title compound, C12H11N5O2, the molecule adopts an E configuration, with the benzene and pyrazine rings located on opposite sides of the N=C double bond. The face-to-face separations of 3.413 (14) and 3.430 (8) Å, respectively between parallel benzene rings and between pyrazine rings indicate the existence of π–π stacking between adjacent molecules. The crystal structure also contains N—H⋯N and C—H⋯O hydrogen bonding.

In the title compound, C 12 H 11 N 5 O 2 , the molecule adopts an E configuration, with the benzene and pyrazine rings located on opposite sides of the N C double bond. The face-to-face separations of 3.413 (14) and 3.430 (8) Å , respectively between parallel benzene rings and between pyrazine rings indicate the existence ofstacking between adjacent molecules. The crystal structure also contains N-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonding.   Table 1 Hydrogen-bond geometry (Å , ).

Comment
Hydrazone and its derivatives have attracted much attention because of their potential application in biology (Okabe et al., 1993;Hu et al., 2001). As part of an ongoing investigation into anti-cancer compounds (Chen et al., 2007), the title compound has recently been prepared in our laboratory and its crystal structure is presented here.
The molecular structure of the title compound is shown in Fig. 1. The molecule adopts an E-configuration, with the benzene and pyrazine rings located on the opposite positions of the N3=C7 double bond, similar to that found in a related structure, (E)-2-Furyl methyl ketone 2,4-dinitrophenylhydrazone (Shan et al., 2008). The pyrazine plane is twisted with respect to the benzene ring by a smaller dihedral angle of 14.25 (10)°.
The partially overlapped arrangement is observed between parallel benzene rings and between parallel pyrazine rings ( Fig. 2), face-to-face separations of 3.413 (14) [for benzene rings] and 3.430 (8) Å [for pyrazine rings] are significantly shorter than van der Waals thickness of the aromatic ring (3.70 Å), and indicate the existence of π-π stacking between the adjacent molecules. Intermolecular N-H···N and weak C-H···O hydrogen bondings are present in the crystal structure (Table 1).
Experimental 4-Nitrophenylhydrazine (0.31 g, 2 mmol) was dissolved in ethanol (10 ml), then H 2 SO 4 solution (98%, 0.5 ml) was added slowly to the ethanol solution with stirring. The solution was heated at about 333 K for several minutes until the solution cleared. An ethanol solution (5 ml) of acetylpyrazine (0.24 g, 2 mmol) was dropped slowly into the above solution with continuous stirring, and the mixture solution was kept at about 333 K for 0.5 h. When the solution had cooled to room temperature, yellow microcrystals appeared. They were separated and washed with cold water three times to get the product 0.40 g. Single crystals of the title compound were obtained by recrystallization from an absolute ethanol solution.

Refinement
Methyl H atoms were placed in calculated positions with C-H = 0.96 Å and torsion angle was refined to fit the electron density, U iso (H) = 1.5U eq (C). Imino H atom was located in a difference Fourier map and refined as riding in its as-found relative position, U iso (H) = 1.2U eq (N). Aromatic H atoms were placed in calculated positions with C-H = 0.93 and refined in riding mode with U iso (H) = 1.2U eq (C). Fig. 1. The molecular structure of (I) with 30% probability displacement ellipsoids (arbitrary spheres for H atoms), dashed line indicates hydrogen bonding. (E)-2-Acetylpyrazine 4-nitrophenylhydrazone