Crystal structure, Hirshfeld surface analysis, interaction energy and energy framework calculations, as well as density functional theory (DFT) computation, of methyl 2-oxo-1-(prop-2-ynyl)-1,2-dihydroquinoline-4-carboxylate

In the crystal of the title compound, C—H⋯O hydrogen bonds link the molecules, enclosing (10) and (16) ring motifs, into layers almost parallel to the bc plane. The layers are further connected by π–π stacking interactions.

In the title molecule, C 14 H 11 NO 3 , the dihydroquinoline core deviates slightly from planarity, indicated by the dihedral angle of 1.07 (3) � between the two sixmembered rings.In the crystal, layers of molecules almost parallel to the bc plane are formed by C-H� � �O hydrogen bonds.These are joined by �-� stacking interactions.A Hirshfeld surface analysis revealed that the most important contributions to the crystal packing are from H� � �H (36.0%),H� � �C/ C� � �H (28.9%) and H� � �O/O� � �H (23.5%) interactions.The evaluation of the electrostatic, dispersion and total energy frameworks indicates that the stabilization is dominated by the dispersion energy contribution.Moreover, the molecular structure optimized by density functional theory (DFT) at the B3LYP/6-311G(d,p) level is compared with the experimentally determined molecular structure in the solid state.The HOMO-LUMO behaviour was elucidated to determine the energy gap.
In continuation of our research work devoted to the study of O-alkylation and N-alkylation reactions involving quinoline derivatives, we report herein the synthesis and the molecular and crystal structures of methyl 2-oxo-1-(prop-2-ynyl)-1,2-dihydroquinoline-4-carboxylate, obtained by an alkylation reaction of methyl 2-oxo-1,2-dihydroquinoline-4-carboxylate using an excess of propargyl bromide as an alkylating reagent in phase transfer catalysis (PTC).Moreover, a Hirshfeld surface analysis and interaction energy and energy framework calculations were performed.The molecular structure optimized by density functional theory (DFT) at the B3LYP/6-311G(d,p) level is compared with the experimentally determined molecular structure in the solid state.

Hirshfeld surface analysis
In order to visualize the intermolecular interactions in the crystal of the title compound, a Hirshfeld surface (HS) analysis (Hirshfeld, 1977) was carried out by using Crystal- The molecular structure of the title compound with the atom-labeling scheme and displacement ellipsoids drawn at the 50% probability level.

Figure 2
A partial packing diagram, viewed down the a axis, with C-H� � �O hydrogen bonds shown as dashed lines.

Figure 3
View of the three-dimensional Hirshfeld surface of the title compound, plotted over d norm in the range from À 0.1226 to 1.1991 a.u.
Explorer (Spackman et al., 2021).In the HS plotted over d norm (Fig. 3), the white surface indicates contacts with distances equal to the sum of the van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distinct contact) than the sum of the van der Waals radii (Venkatesan et al., 2016).The bright-red spots indicate their roles as respective donors and/or acceptors; they also appear as blue and red regions corresponding to positive and negative potentials on the HS mapped over electrostatic potential (Spackman et al., 2008;Jayatilaka et al., 2005), as

Figure 4
View of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential energy in the range from À 0.0500 to 0.0500 a.u., using the STO-3G basis set at the Hartree-Fock level of theory.

Figure 5
The Hirshfeld surface of the title compound plotted over shape-index.

Figure 6
The The Hirshfeld surface analysis confirms the importance of H-atom contacts in establishing the packing.The large number of H� � �H, H� � �C/C� � �H and H� � �O/O� � �H interactions suggest that van der Waals interactions play the major role in the crystal packing (Hathwar et al., 2015).

Interaction energy calculations and energy frameworks
Using CrystalExplorer (Spackman et al., 2021), the intermolecular interaction energies were calculated at the CEB3LYP/631G(d,p) energy level, where a cluster of molecules is generated by applying crystallographic symmetry operations with respect to a selected central molecule within a radius of 3.8 A ˚by default (Turner et al., 2014).The total intermolecular energy (E tot ) is the sum of electrostatic (E ele ), polarization (E pol ), dispersion (E dis ) and exchange-repulsion (E rep ) energies (Turner et al., 2015), with scale factors of 1.057, 0.740, 0.871 and 0.618, respectively (Mackenzie et al., 2017).Energy frameworks combine the calculation of intermolecular interaction energies with a graphical representation of their magnitude (Turner et al., 2015).Energies between molecular pairs are represented as cylinders joining the centroids of pairs of molecules with the cylinder radius proportional to the relative strength of the corresponding interaction energy.Energy frameworks were constructed for E ele (red cylinders), E dis (green cylinders) and E tot (blue cylinders), and are shown in Figs.8(a)-(c).The evaluation of the electrostatic, dispersion  and total energy frameworks indicates that in the title compound the stabilization is dominated by the dispersion energy contribution.

DFT calculations
The optimized structure of the title compound in the gas phase was computed on the basis of density functional theory (DFT) using the standard B3LYP functional and the 6311G(d,p) basis set (Becke, 1993), as implemented in GAUSSIAN09 (Frisch et al., 2009).Comparisons of calculated bond lengths and angles with those of the experimental study are compiled in Table 2.The frontier orbitals were also investigated, and the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals are depicted in Fig. 9.It can be seen that the electron density of the HOMO is mostly distributed within the quinoline moiety, while that of the LUMO is mostly distributed over the carboxylate group.
Other chemistry descriptors (chemical hardness �, softness S, electronegativity � and electrophilicity !) derived from the conceptual DFT calculations are given in Table 3.The HOMO and LUMO are localized in the plane extending from the methyl 2-oxo-1-(prop-2-ynyl)-1,2-dihydroquinoline-4-carboxylate ring.The energy band gap [�E = E LUMO À E HOMO ] (Fig. 9) of the molecule is about À 4.0 eV, with individual frontier molecular orbital energies, E HOMO and E LUMO , of À 6.35 and À 2.35 eV, respectively.The energy frameworks, viewed down the c axis, for a cluster of molecules of the title compound, showing the (a) electrostatic energy, (b) dispersion energy and (c) total energy diagrams, where the b axis is vertical and the c axis is horizontal.The cylindrical radius is proportional to the relative strength of the corresponding energies and was adjusted to the same scale factor of 80 with a cut-off value of 5 kJ mol À 1 within 2 � 2 � 2 unit cells.

Figure 9
The energy band gap of the title compound.

Refinement
Crystal, data collection and refinement details are presented in Table 4. H atoms were included as riding contributions in idealized positions with isotropic displacement parameters tied to those of the attached atoms.Two reflections obscured by the beamstop were omitted from the final refinement.

Figure 10
The molecular moiety used for the database search. sup-3 full two-dimensional fingerprint plots for the title compound, showing (a) all interactions, (b) H� � �H, (c) H� � �C/C� � �H, (d) H� � �O/O� � �H, (e) C� � �C, (f) C� � �O/O� � �C, (g) H� � �N/N� � �H, (h) C� � �N/N� � �C and (i) N� � �O/O� � �N interactions.The d i and d e values are the closest internal and external distances (in A ˚) from given points on the Hirshfeld surface contacts.shown in Fig. 4. The blue regions indicate positive electrostatic potential (hydrogen-bond donors), while the red regions indicate negative electrostatic potential (hydrogen-bond acceptors).The shape-index of the HS is a tool to visualize the �-� stacking interactions by the presence of adjacent red and blue triangles (Fig. 5).The overall two-dimensional fingerprint plot [Fig.6(a)] and those delineated into H� � �H, H� � �C/C� � �H, H� � �O/O� � �H, C� � �C, C� � �O/O� � �C, H� � �N/N� � �H, C� � �N/ N� � �C and N� � �O/O� � �N contacts (McKinnon et al., 2007) are illustrated in Figs.6(b)-(i), respectively, together with their relative contributions to the Hirshfeld surface.The most important interaction is H� � �H, contributing 36.0% to the overall crystal packing, which is reflected in Fig. 6(b) as widely scattered points of high density due to the large hydrogen content of the molecule with the tip at d e = d i = 1.22A ˚.In the absence of C-H� � �� interactions, the pair of characteristic wings resulting in the fingerprint plot delineated into H� � �C/ C� � �H contacts [Fig.6(c)] have a 28.9% contribution to the HS, with the tips at d e + d i = 2.68 A ˚.The pair of the scattered points of spikes resulting in the fingerprint plot delineated into H� � �O/O� � �H contacts [Fig.6(d)], with a 23.5% contribution to the HS, has an almost symmetric distribution of points, with the tips at d e + d i = 2.44 A ˚.The C� � �C contacts [Fig.6(e)] appear as an arrow-shaped distribution of points and have a contribution of 7.0% to the HS with the tip at d e = d i = 1.69A ˚.The tiny spikes of C� � �O/O� � �C contacts [Fig.6(f)], with a 2.5% contribution to the HS, are visible at d e + d i = 3.58 A ˚. Finally, the H� � �N/N� � �H [Fig.6(g)], C� � �N/N� � �C [Fig.6(h)] and N� � �O/O� � �N [Fig.6(i)] contacts contribute 1.4, 0.4 and 0.4%, respectively, to the HS.The Hirshfeld surface representations with the function d norm plotted onto the surface are shown for the H� � �H and H� � �C/C� � �H interactions in Figs.7(a)-(c), respectively.

Figure 7 The
Figure 7 The Hirshfeld surface representations with the function d norm plotted onto the surface for (a) H� � �H, (b) H� � �C/C� � �H and (c) H� � �O/O� � �H interactions.

A
Figure 8 parallel to (104), but it has no C-H� � �Cl hydrogen bonds or �-� stacking interactions.The halogen-free analogue of ROKCIG (ROKCOM; Filali Baba et al., 2019) uses C-H� � �O hydrogen bonds to form molecular bands along the c axis, which are connected by weak �-� interactions.

Table 2
Comparison (X-ray and DFT) of selected bond lengths and angles (A ˚, � ).

Table 3
Calculated energies for compound (I).

Table 4
Experimental details.
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