Crystal structure, Hirshfeld surface analysis and DFT studies of 1,3-bis[2-methoxy-4-(prop-2-en-1-yl)phenoxy]propane

Two different molecules with point group symmetry 2 are present in the crystal structure of the title compound. Each independent molecule forms chains parallel to the b axis with its symmetry-related counterparts through C—H⋯π(ring) interactions.

The asymmetric unit of the title compound, C 23 H 28 O 4 , comprises two halfmolecules, with the other half of each molecule being completed by the application of twofold rotation symmetry. The two completed molecules both have a V-shaped appearance but differ in their conformations. In the crystal, each independent molecule forms chains extending parallel to the b axis with its symmetry-related counterparts through C-HÁ Á Á(ring) interactions. Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from HÁ Á ÁH (65.4%), HÁ Á ÁC/CÁ Á ÁH (21.8%) and HÁ Á ÁO/OÁ Á ÁH (12.3%) interactions. Optimized structures using density functional theory (DFT) at the B3LYP/6-311 G(d,p) level are compared with the experimentally determined molecular structures in the solid state. The HOMO-LUMO behaviour was elucidated to determine the energy gap.
As a continuation of our research devoted to the study of oalkylation reactions involving eugenol derivatives, we report herein the synthesis, molecular and crystal structures of the title compound, (I). Hirshfeld surface analysis and a density functional theory (DFT) study carried out at the B3LYP/6-

Hirshfeld surface analysis
In order to quantify the intermolecular interactions in the crystal of (I), a Hirshfeld surface (HS) analysis (Hirshfeld,  The two independent molecules of (I) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Overlay of the two independent half-molecules, showing their different conformations. Molecule A is in light, molecule B in dark colours.

Figure 4
A partial packing diagram viewed along the a axis with intermolecular interactions depicted as in Fig. 3. 1977; Spackman & Jayatilaka, 2009) was carried out using Crystal Explorer 17.5 (Turner et al., 2017). In the HS plotted over d norm (Fig. 5), the white surface indicates contacts with distances equal to the sum of van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distinct contact) than the van der Waals radii, respectively (Venkatesan et al., 2016). The bright-red spots appearing near C16 and hydrogen atom H10B indicate their roles as the donor and/or acceptor groups in hydrogenbonding contacts. The shape-index of the HS is a tool to visualize possiblestacking interactions by the appearance of adjacent red and blue triangles. The absence of such triangles suggests that there are no notableinteractions in (I) (Fig. 6). The overall two-dimensional fingerprint plot, Fig. 7a Table 1 Hydrogen-bond geometry (Å , ).

Figure 6
Hirshfeld surface of the title compound plotted over shape-index.

Figure 5
View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.1048 to 1.1789 a.u..

Figure 7
The full two-dimensional fingerprint plots for the title compound   Fig. 8a-c, respectively.

DFT calculations
The density functional theory (DFT) optimized molecular structures of (I) were computed in the gas phase on the basis of standard B3LYP functionals and 6-311 G(d,p) basis-set calculations (Becke, 1993) as implemented in GAUSSIAN 09 (Frisch et al., 2009). The theoretical and experimental results for molecule A are in good agreement (Table 3) Table 3 Comparison of selected bond lengths and angles (Å , ) in the experinentally determined and computed molecular structures.

Figure 9
The shapes of HOMO and LUMO orbitals in one of the molecules in (I).
research communications If the energy gap ÁE between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is small, the molecule is highly polarizable and has high chemical reactivity. Numerical values of E HOMO and E LUMO , ÁE = E LUMO -E HOMO , electronegativity (), hardness (), potential (), electrophilicity (!) and softness () for (I) are collated in Table 4. The significance of and is to evaluate both the reactivity and stability. The shapes of the HOMO and the LUMO of molecule A, together with their energy levels are shown in Fig. 9.

Synthesis and crystallization
1,3-Dibromopropane (0.2 ml, 1.61 mmol) was added to a solution of eugenol (0.5 ml, 3.23 mmol), tetrabutylammonium chloride (50 mg) and sodium hydroxide solution (5%) in benzene as solvent (20 ml). The mixture was stirred at 293 K for 6 h, and then was extracted three times with dichloromethane (15 ml). The residue was purified by column chromatography on silica gel using a mixture of hexane/ethyl acetate (v/v = 97/3) as eluent. Colourless crystals were isolated when the solvent was allowed to evaporate (yield: 86%).

Refinement
Details including crystal data, data collection and refinement are summarized in Table 5. Hydrogen atoms were located in a difference-Fourier map and were refined freely.

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. 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 > 2sigma(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.