Synthesis and structure of (E)-N-(4-methoxyphenyl)-2-[4-(3-oxo-3-phenylprop-1-en-1-yl)phenoxy]acetamide

The asymmetric unit of the title compound, C24H21NO4, contains four molecules. Each molecule displays intramolecular N—H⋯O hydrogen bonds and C—H⋯O interactions. The crystal packing is characterized by C—H⋯O hydrogen-bonding interactions, resulting in chain formation in the [001] direction, and C—H⋯π interactions.


Structural commentary
The title compound crystallizes in the monoclinic space group Cc. The asymmetric unit contains four molecules and is illu-strated in Fig. 1. In the following discussion, molecule A includes atoms C1-C29, molecule B atoms C30-C58, molecule C atoms C59-C87 and molecule D atoms C85-C116. All four molecules exist in the (E)-configuration and display intramolecular N-HÁ Á ÁO hydrogen bonds and C-HÁ Á ÁO interactions (Table 1). With the presence of the N-HÁ Á ÁO hydrogen bond, one would assume the central and the methoxy-substituted phenyl rings to be almost coplanar. This is not the case, with dihedral angles between the least-squares planes through the two rings being 17.27 (19), 45.8 (2), 38.91 (19) and 14.9 (2) for molecules A-D, respectively. A similar trend is observed for the two phenyl rings linked by the propenone unit, with dihedral angles of 42.8 (2), 29.0 (2), 26.3 (2) and 43.2 (2) for molecules A-D, respectively. Fig. 2 shows an overlay diagram of the four molecules A-D [r.m.s. deviations between 0.0887 Å for the fit of A and D, and 0.6695 Å for the fit of C and D as calculated using Mercury (Macrae et al., 2020)]. The largest differences are observed for the terminal groups. At one end, the phenyl rings of molecules A and D, and of B and C have a similar orientation. At the other side, the terminal methyl group is oriented differently for molecule C. Overlay diagram of the four independent molecules A (green), B (blue), C (red) and D (yellow) comprising the asymmetric unit. H atoms are hidden for clarity.  The molecular structure for the four molecules present in the asymmetric unit of the title compound, showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level. two are involved in a chain formation in the [001] direction through C arom -HÁ Á ÁO methoxy interactions [graph-set C (21)]. In addition, molecules A and B, and C and D interact through C arom -HÁ Á ÁO amide interactions.
A Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were performed in order to further investigate the supramolecular network. The Hirshfeld surface calculated using CrystalExplorer (Turner et al., 2017) and mapped over d norm is for each molecule in the asymmetric unit given in Fig. 5. These surfaces show the expected bright-red spots near atoms O14, O51, O97, O109, H31, H56, H75 and H114 involved in the C-HÁ Á ÁO hydrogen-bonding interactions described above. In addition, faint-red spots reveal some additional short HÁ Á ÁH, CÁ Á ÁC and HÁ Á ÁO contacts, as indicated in Fig. 5 View of the C-HÁ Á Á interactions in the crystal packing of the title compound. Colour codes used: cyan for ring C1-C6; orange for ring C30-C35; green for ring C45-C50; magenta for ring C59-C64; yellow for ring C74-C79; brown for ring C88-C93. See Table 1 for further details. Table 1 Hydrogen-bond geometry (Å , ).

Figure 5
The Hirshfeld surface mapped over d norm for the four molecules in the asymmetric unit of the title compound. double bond. The histogram of the dihedral angle between the two phenyl rings shows two maxima at $15 and $55 (Fig. 6a).
For the 3-(4-oxyphenyl)prop-2-en-1-one core of the title compound ( Fig. 6b) 159 hits were found. The configuration about the double bond is always E with C-C C-C torsion angles between À168.9 and 169.8 (Fig. 6c). For the C C-C O torsion angle, the majority display an s-cis conformation (141 hits or 88.7%), in contrast to an s-trans conformation (18 hits, 11.3%) (Fig. 6d).
In order to verify the frequency of having four molecules in the asymmetric unit, a search in the CSD resulted in only 0.52% of the entries having Z 0 = 4 (0.62% for Z 0 ! 4).
The reaction of 4-hydroxybenzaldehyde, 1, and acetophenone, 2, to obtain chalcone 3 was carried out according to the procedure described in the literature (Dimmock et al., 1998;Bui et al., 2020). Physical properties and IR and 1 H-NMR spectroscopic data of chalcone 3 are in agreement with data in the literature (Dimmock et al., 1998;Ohkatsu et al., 2008;Bui et al., 2020). The existence of chalcone 3 in the (E)-configuration is not only clear from the IR spectrum but also the 1 H-NMR spectrum. While the IR spectrum of 3 shows absorptions at 972 cm À1 corresponding to bending vibrations of a trans-alkene, its 1 H-NMR spectrum shows two doublet signals ( 7.73 and 7.75) with a spin-spin coupling constant of 17.0 Hz in accordance with a trans position.
The mass spectra of 4 showed pseudo-molecular peaks in agreement with the molecular formula of C 24 H 22 NO 4 (M+H) + . The IR, 1 H-NMR and 13 C-NMR spectra of the product match with the proposed structure. Notably, in the IR spectrum of 4 two new absorption bands appear, one at 3381 (NH) and the other at 1680 cm À1 (C O amide). In comparison to the 1 H-NMR spectrum of 3, the spectrum of 4 contains some extra signals in the aromatic area. Moreover, the signal of the CH 2 group (singlet with integration of 2H) is observed at 4.77. The trans configuration of 4 was also confirmed by the coupling constant J ab ' 17.0 Hz of the vinylic protons.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms H15, H44, H73 and H102 were located from difference electron-density maps and refined freely [for H44, an N44-H44 distance restraint of 0.87 (2) Å was used]. The other H atoms were placed in idealized positions and included as riding contributions with U iso (H) values of 1.2U eq or 1.5U eq of the parent atoms, with C-H distances of 0.93 (aromatic), 0.97 (CH 2 ) and 0.96 Å (CH 3 ). In the final cycles of refinement, 26 outliers were omitted. Refinement of the Flack parameter [0.1 (3)] did not allow the unambiguous determination of the chirality of the spatial molecular arrangement in space group Cc.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.