(2E,4E)-2-Cyano-5-dipropylamino-N,N-dimethylpenta-2,4-dienamide

In the title compound, C14H23N3O, the n-propyl group is disordered over two orientations with an occupancy ratio of 0.778 (3):0.222 (3). In the crystal, molecules are linked by pairs of weak C—H⋯O interactions into inversion dimers with an R 2 2(14) graph-set motif.

In the title compound, C 14 H 23 N 3 O, the n-propyl group is disordered over two orientations with an occupancy ratio of 0.778 (3):0.222 (3). In the crystal, molecules are linked by pairs of weak C-HÁ Á ÁO interactions into inversion dimers with an R 2 2 (14) graph-set motif.

Xian-Feng Zhou and Xiao-Hua Du Comment
The title compound is a useful intermediate for the synthesis of 2-chloro-N,N-dimethylnicotinamide derivatives, which are widely used in syntheses of pharmaceutics and pesticides (Bryson et al., 1976). In order to establish conformational details of the title molecule, its crystal structure has been determined. In the crystal structure, the n-propyl composed of C12\C13\C14 is disordered over two positions with different occupancies that are 0.778 (3) and 0.222 (3) for the chains A and B, respectively. Both disordered chains are related approximately by a non-crystallographic symmetry plane. As shown in Fig. 1, O1 is deviated by 3.6 (4) Å from the plane composed of C1\C2\C3\C4\C5.
These examples show that the disorder of n-propyl chain is rather common in molecules containing such a motif as it happens to be present in the title structure ( Fig. 1).
There are present only weak intermolecular interactions in the structure among which C5-H5···O1 i is most prominent (the symmetry code i: 1-x, 1-y, 1-z). As shown in Fig. 2, a centrosymmetric dimer about the crystallographic inversion centre is formed by a pair of these hydrogen bonds with the graph set motif R 2 2 (14) (Etter et al., 1990).

Refinement
The initial determination of the structural model yielded the non-disordered non-hydrogen atoms in the structure as well as the atoms C12a\C13a\C14a which form the dominant part of the disordered n-propyl chain. The difference electron density map has shown other maxima corresponding to the atoms of the less occupied disordered chain supplementary materials C12b\C13b\C14b. Moreover, the difference electron density map has also shown the hydrogen positions of all the hydrogens with exception of those pertinent to the less occupied n-propyl chain. The non-hydrogen atoms of both disoredered chains were related approximately by reflection through a non crystallographic mirror plane. The non-proper symmetry that related the disordered chains has been respected in the refinement which assumed that both chains were identical except for the inversion between them. Thus, the individual parameters of the atoms in the chain were refined in addition to the positional parameters of each of the disordered chain. Moreover, the occupational parameters of both chains were constrained to equal to 1.0. The described procedure infers that the positions of the methyl hydrogens of C14b which are not observable in the difference electron density maps can be biased because the methyl hydrogens pertinent to C14a and C14b need not be related by the reflection through the non-crystallographic mirror plane. The riding-atom approximation has been used for all the H-atoms in the structure: The used constraints are C sp 2 -H sp 2 =0.93, C methyl H methyl =0.96, C methylene -H methylene =0.97 Å. U iso H sp 2 =1.2U eq C sp 2 , U iso H methylene =1.2U eq C methylene , U iso H methyl =1.5U eq C methyl .

Figure 1
The title molecule with the atomic labelling scheme. The displacement ellipsoids are drawn at the 50% probability level. The graph set motif R 2 2 (14) showing the hydrogen bonds C5-H5···O1 i . The symmetry code: (i): 1-x, 1-y, 1-z. Weighting scheme based on measured s.u.'s w = 1/(σ 2 (I) + 0.0004I 2 ) (Δ/σ) max = 0.008 Δρ max = 0.17 e Å −3 Δρ min = −0.14 e Å −3 Extinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974) Extinction coefficient: 21000 (2000) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.

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