Crystal structure, DFT study and Hirshfeld surface analysis of ethyl 6-chloro-2-ethoxyquinoline-4-carboxylate

The title quinoline derivative is essentially planar with the ethyl acetate mean plane making a dihedral angle of 5.02 (3)° with the ethyl 6-chloro-2-ethoxyquinoline mean plane. In the crystal, offset π–π interactions involving inversion-related pyridine rings [centroid-to-centroid distance = 3.4731 (14) Å] link the molecules into columns along the c-axis direction.


Hirshfeld surface analysis
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were performed with Crystal-Explorer17 (Turner et al., 2017). Internal and external (d i and d e ) contact distances from the Hirshfeld surface to the nearest atom inside and outside enables the analysis of the intermolecular interactions through the mapping of d norm . The Hirshfeld surfaces (HS) mapped over the electrostatic potential (À0.0534 to 0.0319 atomic units) and d norm (À0.0210 Table 1 Hydrogen-bond geometry (Å , ).   (a) The molecular structure of the title compound, with the atom labelling and displacement ellipsoids drawn at the 50% probability level. The dashed line represents the intramolecular C-HÁ Á ÁO interaction (Table 1). (b) The essentially planar structure of the title compound.
to 1.4779 arbitrary units) are shown in Fig. 3a and 3b. The red spots on the Hirshfeld surface indicate interactions involved in HÁ Á ÁO contacts. Thestacking is confirmed by the small blue regions surrounding bright red spots in the aromatic ring in Fig. 3c, the Hirshfeld surface mapped over the shape-index, and by the flat regions around the aromatic regions in Fig. 3d, the Hirshfeld surface mapped over the curvedness.
There are no significant classical intermolecular contacts present in the crystal according to the analysis of the crystal structure using PLATON (Spek, 2009). However, from the Hirshfeld surface analysis and the two-dimensional fingerprint plots it can be seen that HÁ Á ÁH, CÁ Á ÁH, ClÁ Á ÁH and OÁ Á ÁH contacts ( Fig. 4) contribute to the cohesion of the crystal structure. The two-dimensional fingerprint plots are given in Hirshfeld surface of the title compound mapped over: (a) electrostatic potential, (b) d norm , (c) shape-index and (d) curvedness.

Synthesis and crystallization
A solution of 0.5 g (1.99 mmol) of ethyl 6-chloro-2-oxo-1,2dihydroquinoline-4-carboxylate in 25 ml of DMF was mixed with 0.3 ml (3.98 mmol) of bromoethane, 0.55 g (3.98 mmol) of K 2 CO 3 and 0.06 g (0.199 mmol) of tetra-n-butylammonium bromide (TBAB). The reaction mixture was stirred at room temperature in DMF for 24 h. After removal of salts by filtration, the DMF was evaporated under reduced pressure and the residue obtained was dissolved in dichloro-methaneÁThe organic phase was dried over Na 2 SO 4 then concentrated in vacuo. The resulting mixture was chromatographed on a silica gel column [eluent: ethyl acetate/hexane (1:9 v/v)]. Colourless crystals were obtained when the solvent was allowed to evaporate (yield: 32%).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were positioned geometrically and refined using a riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other H atoms. A rotating group model was applied to the methyl groups.  program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Ethyl 6-chloro-2-ethoxyquinoline-4-carboxylate
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.30 e Å −3 Δρ min = −0.32 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 )