4-Butoxy-N′-[1-(4-methylphenyl)ethylidene]benzohydrazide

The molecule of the title compound, C20H24N2O2, exists in a trans conformation with respect to the C=N bond. The dihedral angle between the benzene rings is 79.0 (1)°. In the crystal, N—H⋯O hydrogen bonds link the molecules into chains propagating in [001]. Two weak C—H⋯O interactions also occur.

The molecule of the title compound, C 20 H 24 N 2 O 2 , exists in a trans conformation with respect to the C N bond. The dihedral angle between the benzene rings is 79.0 (1) . In the crystal, N-HÁ Á ÁO hydrogen bonds link the molecules into chains propagating in [001]. Two weak C-HÁ Á ÁO interactions also occur.
Aroylhydrazones are important compounds for drug design, as possible ligands for metal complexes, catalysis and also for the syntheses of heterocyclic compounds (Barbazan et al., 2008;Dang et al., 2007). The ease of preparation, increased hydrolytic stability relative to imines, and tendency toward crystallinity are all desirable characteristics of hydrazones. Due to these positive traits, the chemical properties of aroylhydrazones have been extensively studied for a long time. Acylhydrazones possess two connected nitrogen atoms of different nature and a carbon-nitrogen double bond that is conjugated with a lone electron pair of the terminal nitrogen atom. These structural fragments are mainly responsible for the physical and chemical properties of hydrazones. The introduction of functional groups in the hydrazone molecules expands the scope of use in coordination chemistry.
Aroylhydrazones are potential ligands due to having a number of bonding sites. They can act a neutral or monoanionic bidentate or tridentate ligand depending on the substituents and the reaction conditions. Furthermore, abilities to coordinate to metals either in keto (I) or enol (II) tautomeric form make them attractive as ligands. This compound is in the keto form in the solid state. The keto hydrazone moiety may coordinate to metals in the keto amide or deprotonated enolimine form. Hydrazones typically act as bi-and tridentate, mono or biprotic depending on the reaction conditions (Sreeja et al., 2003;Naskar et al., 2004;Gup & Kirkan, 2005).
As can be seen from the packing diagram ( Fig. 2), inter-molecular N-H···O and C-H···O hydrogen bonds (Table 1) link the molecules and these hydrogen bonds may be effective in the stabilization of the crystal structure. In these interactions, there are the N1, C16 and C17 atoms of molecule as donor and the O2 atom of the other molecules as acceptor ( Experimental 4′-Methylacetophenon (4 mmol, 0.552 g) dissolved in ethanol (10 ml) was added dropwise to a suspension of 4-hydroxybenzohydrazide (4 mmol, 0.608 g) with two drops of glacial acetic acid in ethanol (40 ml) in room temperature. The reaction mixture was refluxed for further 8 h and the colorless product was filtered. The pure hydrazone was collected by crystallization from ethanol.

Refinement
The H atoms were positioned geometrically, with C-H = 0.95 Å, N-H = 0.88 Å, and and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C,N). Also, the methyl H atoms were positioned geometrically, with C-H = 0.98 Å and U iso (H) = 1.5U eq (C). The absolute structure could not be determined and 1089 Friedel pairs were averaged before the last refinement.

Figure 1
An ORTEP drawing of molecular structure with the crystallographic numbering scheme. Thermal ellipsoids are drawn at 30% probability levels.    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 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.