Reaction of primary aromatic amines, formaldehyde, and dimedone in the presence of mineral acid produces a mixture of 1,8-dioxodecahydroacridines (A) and 1,8-dioxooctahydroacridinium quaternary salts (B) [1]. Syrmnetric decahydroacridinediones without a substituent at the nitrogen atom have also been prepared by reacting the imine of dimedone with aldehydes in acetic acid [2]. Additional investigations revealed compound A as reaction intermediate which transform into salt B upon longer heating.Quaternary salt B reacts with bases to produce bright red anhydrobase C, which is also produced from A via oxidation of its alcohol solutions. The transformation occurred according to the following scheme:The structures of the prepared compounds were studied using IR, UV, and PMR spectra [1]. Therefore, it seemed interesting to investigate the geometry and electronic structures of A, B, and C using quantum-chemical calculations. The effective charges were calculated using the CNDO/2 method. The geometry of compounds was calculated using the AM 1 method from the Hyperchem program set [3]. Models without the N-phenyl substituent (1,2,3) and with N-phenyl substituents (4, 5, 6) were calculated in order to reveal the effect of the N-phenyl substituent on the structure. As seen from the diagrams provided, compounds 1, 2, 4, and 5, in contrast with 3 and 6, have symmetric structures.Effective Charges. The nitrogen atom is characterized by a high negative charge, that is decreased by the N-phenyI substituent. The greatest effect is seen for the compounds of B group. Only for group B does the N-phenyl group affect the charge on the carbon atoms of the pyridine ring. It reduces the negative charges (electron-withdrawing effect). The N-phenyl substituent decreases also the effective charge on the oxygen atom of the carbonyl group (in group B, the N-phenyl substituent has no effect in the other groups).
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