Crystal structure, Hirshfeld surface analysis and density functional theory study of 1-nonyl-3-phenylquinoxalin-2-one

The phenyl-quinoxaline moiety in the title compound is not planar. In the crystal, C—H⋯O hydrogen bonds between neighboring quinoxaline rings form chains along the a axis direction.

In the title molecule, C 23 H 28 N 2 O, the phenyl ring is inclined to the quinoxaline ring system at a dihedral angle of 20.40 (9) . In the crystal, C-HÁ Á ÁO interactions between neighbouring molecules form chains along the a-axis direction. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from HÁ Á ÁH (70.6%), HÁ Á ÁC/CÁ Á ÁH (15.5%) and HÁ Á ÁO/OÁ Á ÁH (4.6%) interactions. The optimized structure calculated using density functional theory at the B3LYP/6-311 G(d,p) level is compared with the experimentally determined structure in the solid state. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gap is 3.8904 eV. Part of the n-nonyl chain attached to one of the nitrogen atoms of the quinoxaline ring system shows disorder and was refined with a double conformation with occupancies of 0.604 (11) and 0.396 (11).

Chemical context
Nitrogen-based structures have attracted increased attention in structural and inorganic chemistry in recent years because of their interesting properties (Chkirate et al., 2019(Chkirate et al., , 2020a(Chkirate et al., ,b, 2021(Chkirate et al., , 2022Bouzian et al., 2021). The family of quinoxalines, particularly those containing the quinoxalin-2-one moiety, is important in medicinal chemistry because of their wide range of pharmacological applications, including their use as antitumor active agents (Galal et al., 2014), and their antimicrobial (Carta et al., 2003) and biological (Carta et al., 2002) activity. In particular, 3-phenylquinoxaline derivatives are used as anticancer drugs (Abad, Sallam et al., 2021). They also have antifolate activities (Corona et al., 2008). Given the wide range of therapeutic applications for such compounds, and in a continuation of the work already carried out on the synthesis of compounds resulting from quinoxalin-2-one (Al Ati et al., 2021), a similar approach gave the title compound, 1-nonyl-3phenylquinoxalin-2-one C 23 H 28 N 2 O, (I). Besides the synthesis, we also report the molecular and crystal structures along with a Hirshfeld surface analysis and a density functional theory computational calculation carried out at the B3LYP/6-311G(d,p) level. ISSN 2056-9890
The CrystalExplorer program (Turner et al., 2017) was used to further investigate and visualize the intermolecular interactions of (I). The Hirshfeld surfaces for the major and minor occupancy components plotted over d norm are shown in Fig. 4. The Hirshfeld surface of the major component ( Fig. 4a) is dominated by white regions representing contacts equal to the van der Waals separation and shows only one red spot (close contacts with a negative d norm value) indicative of a H16BÁ Á ÁH16B iii contact [1.995 Å ; symmetry code: (iii) 2 À x, 2 À y, 2 À z]. A similar observation is made for the minor component ( Fig. 4b) where the tiny red spot represents a H15BÁ Á ÁH13B i contact (2.316 Å ).
The overall two-dimensional fingerprint plots (McKinnon et al., 2007) for the two components are shown in Fig. 5a and b, while those delineated into HÁ Á ÁH and HÁ Á ÁC/CÁ Á ÁH contacts are illustrated in Fig. 5c

Figure 2
Partial view of the crystal packing of the title compound showing the C-HÁ Á ÁO interaction (red dashed lines) and chain formation in the a-axis direction. Only the major component of the n-nonyl chain is shown. Symmetry codes: (i) 1 + x, y, z; (ii) À1 + x, y, z.

Figure 1
Molecular structure of the title compound with the atom-labelling scheme and ellipsoids drawn at the 50% probability level. The disordered component of the n-nonyl chain with occupancy 0.396 (11)

Density functional theory calculations
The structure in the gas phase of the title compound was optimized by means of density functional theory. The density functional theory calculation was performed by the hybrid B3LYP method and the 6-311 G(d,p) basis-set, which is based on Becke's model (Becke, 1993) and considers a mixture of the exact (Hartree-Fock) and density functional theory exchange utilizing the B3 functional, together with the LYP correlation functional (Lee et al., 1988). After obtaining the converged geometry, the harmonic vibrational frequencies were calculated at the same theoretical level to confirm that the number of imaginary frequencies is zero for the stationary point. Both the geometry optimization and harmonic vibrational frequency analysis of the title compound were performed with the GAUSSIAN 09 program (Frisch et al., 2009). Theoretical and experimental results related to bond lengths and angles, which are in good agreement, are summarized in Table 2. Calculated numerical values for the title compound, including electronegativity (), hardness (), ionization potential (I), dipole moment (), electron affinity (A), electrophilicity (!) and softness (), are collated in Table 3. The electron transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) energy level is shown in Fig. 6. The HOMO and LUMO are localized in the plane extending over the whole 1-nonyl-3-phenylquinoxalin-2-one system. The energy band gap [ÁE = E LUMO À E HOMO ] of the molecule is 3.8904 eV, and the frontier molecular orbital energies, E HOMO and E LUMO , are À6.1155 and À2.2251 eV, respectively.  HOMO-LUMO and the energy band gap of the title compound. Table 2 Comparison (X-ray and density functional theory) of selected bond lengths and angles (Å , ).  (1) for the two molecules present in the asymmetric unit. For ASAZEC, the dihedral angle is 12.90 (4) and no disorder is observed in the n-octyl chain, which could be the consequence of the data collection being undertaken at 150 (2) K. Despite the similarity to the title compound, ASAZEC crystallizes in space group C2/c and the molecules are linked by C-HÁ Á Á interactions and form stacks in the baxis direction.

Synthesis and crystallization
To a solution of 3-phenylquinoxalin-2(1H)-one (0.5 g, 2.25 mmol) in dichloromethane (20 ml) were added 1-chlorononane (0.2 ml, 2.25 mmol), sodium hydroxide (0.1 g, 2.25 mmol) and a catalytic quantity of tetra-n-butylammonium bromide. The reaction mixture was stirred at room temperature for 24 h. The solution was filtered and the solvent removed under reduced pressure. The residue thus obtained was chromatographed on a silica gel column using a hexane/ ethyl acetate 9:1 mixture as eluent. The solid obtained was recrystallized from ethanol to afford colourless crystals (yield: 70%

Refinement
Crystal data, data collection and structure refinement details are given in Table 4. C-bound H atoms were positioned geometrically (C-H = 0.93-0.97 Å ) and included as riding contributions with isotropic displacement parameters fixed at 1.2 times U eq of the parent atoms (1.5 for methyl groups). During the refinement, the difference-Fourier map revealed disorder for atoms C13, C14 and C15 of the nonyl chain and two conformations were refined with distance restraints (1.512 Å ) for the C-C bonds involved and RIGU restraints for the nonyl chain C11-C17. At the end of the refinement, the occupancy factors of the two components converged to 0.604 (11) and 0.396 (11) and the final difference-Fourier map showed no residual peaks of chemical significance.

Funding information
LVM thanks the Hercules Foundation for supporting the purchase of the diffractometer through project AKUL/09/ 0035.

1-Nonyl-3-phenylquinoxalin-2-one
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.37 e Å −3 Δρ min = −0.45 e Å −3 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.

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