Crystal structure, Hirshfeld surface and frontier molecular orbital analysis of 10-benzyl-9-(4-hydroxy-3-methoxyphenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione

In the acridinedione core of the title molecule, C31H35N1O4, the central ring adopts a flattened-boat conformation, whereas the cyclohexenone rings adopt envelope conformations.

In the fused ring system of the title molecule, C 31 H 35 NO 4 , the conformation of the central dihydropyridine ring is intermediate between boat and envelope with the N and the opposite C atoms lying out of the basal plane. The conformations of terminal rings are close to envelope, with the atoms substituted by two methyl groups as the flaps. In the crystal, the molecules are linked by O-HÁ Á ÁO hydrogen bonds into helical chains. The Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from HÁ Á ÁH (63.2%), OÁ Á ÁH/HÁ Á ÁO (20.1%) and CÁ Á ÁH/HÁ Á ÁC (14.4%) contacts. Quantum chemical calculations of the frontier molecular orbitals were carried out to characterize the chemical reactivity of the title compound.

Structural commentary
The title compound (Fig. 1) crystallizes in the monoclinic space group P2 1 /n with Z = 4. The conformation of the central dihydropyridine ring is intermediate between boat and envelope: four atoms (C8, C9, C17 and C18) form the basal plane with a deviation of 0.008 (2) Å for all of them, whereas atoms N1 and C16 deviate from this plane by 0.168 (2) and 0.476 (2) Å , respectively. The conformations of the terminal C8-C13 and C17-C22 rings are close to envelope with C12 and C20, respectively, as the flap atoms. The basal planes of these envelopes are twisted, and the deviations of corresponding atoms from their least-squares planes are between 0.005 (2) and 0.100 (2) Å . The N1 atom has an essentially planar environment, deviating from the plane through atoms C7, C8 and C18 by only 0.018 (2) Å . The bond lengths in the N1-C8-C9-C10-O2 and N1-C18-C17-C22-O chains indicate -conjugation of N1 with the carbonyl groups C10 O2 and C22 O1 (Table 1). All other bond lengths and angles in the title structure are within the ranges normal for analogous compounds (Allen et al., 1987;Thamotharan et al., 2021;Allah et al., 2021;Mohamed et al., 2013;Akkurt et al., 2014).

Figure 2
Packing

Figure 3
View of the three-dimensional Hirshfeld surface of the title molecule plotted over d norm in the range À0.436 to 1.583 a.u.

Figure 4
View of the three-dimensional Hirshfeld surface of the title molecule plotted over electrostatic potential energy in the range À0.0500 to 0.0500 a.u. calculated with the STO-3 G basis set at the Hartree-Fock level of theory. The hydrogen-bond donating and acceptor areas are viewed as blue and red regions, respectively, around atoms, corresponding to positive and negative potentials.
index of the title molecule are listed in Table 4. The electrophilicity index value of 3.3429 eV shows the global electrophilic nature of the molecule. Based on the wide band gap and chemical hardness value of 2.0174 eV, the title molecule seems to be hard.

Synthesis and crystallization
A mixture of benzylamine (0.214g, 2 mmol), 4-hydroxy-3methoxybenzaldehyde (0.304g, 2 mmol) and 5,5-dimethylcyclohexane-1,3-dione (0.56g, 4 mmol) was dissolved in 25 ml of acetic acid. The solution was refluxed for 2 h with the reaction being monitored by TLC. After the reaction was about to the end, the reaction mixture was poured into 150 ml of ice-cold water, stirred at 298-303K for 10 min and then kept at room temperature for 12 h.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. Hydrogen atoms were fixed geometrically and treated as riding atoms, with C-H = 0.93-0.97 Å and U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl). The frontier molecular orbitals of the title molecule.

Table 4
The global reactivity descriptors of the title compound (eV).  Table 3 The frontier molecular orbital energies of title compound.