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The mechanism and regioselectivity of the Diels–Alder cycloaddition reaction between 9- (methoxymethyl)anthracene and citraconic anhydride are explored using the valuable density functional theory (DFT) methods. The solvent effects are considered using the polarizable continuum model in the toluene solution. Due to a small electrophilicity difference of the reactants, the reaction has a low polar character. The investigated Diels–Alder reaction has a normal electron demand character. Depending on the respective position of substituents in the cycloadducts (head-to-head (ortho) or head-to-tail (meta)) the reaction can be progressed via two different pathways: ortho and meta. Due to a very high activation energy, the meta pathway is rejected. The product of the ortho pathway is demonstrated to be the final product of the reaction in the toluene solution. The obtained DFT results are in good agreement with the experimental results.

Two Schiff bases are newly prepared by the condensation of 2-chloro-3-quinolinecarboxaldehyde with ethylenediamine and 1,4-butanediamine. The Schiff bases are characterized by the elemental analysis, IR, 1H and 13CNMR, UV-Vis, and fluorescence spectroscopies. Structural parameters together with the theoretical assignment of their vibrational frequencies and NMR chemical shifts are determined using density functional theory (DFT) approaches. There is good consistency between the DFT-calculated results and the experimental data, confirming the validity of the optimized geometries for the investigated Schiff bases. Optimized geometries of two Schiff bases are not planar, however, the substitutions are essentially in the same plane with the pyridine rings. Shapes of the frontier orbitals are determined using the natural bond orbital (NBO) analysis. Due to a high energy gap between the frontier orbitals, both Schiff bases are stable. Based on the Fukui function analysis, two Cl atoms and two azomethine nitrogen atoms are four suitable donor atoms for coordination to metal ions. Effects of the temperature and pH on the UV-Vis absorbance and fluorescence intensity of the Schiff bases are studied in a DMSO solution.