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Comparative DFT computations were studied between Paracetamol (PA) and its analogues such as p-nitroacetanilide (PA-NO 2 ), p-bromoacetanilide (PA-Br) and N-acetylanthranilic acid (NAA) which can be considered also as analogue of Aspirin (ASP). As well, Thio-Aspirin, Acetyl-Thio-Salicylic acid, (TASP) is another analogue of ASP. From DFT studies, it has been concluded that PA and its analogues have the predominant trans-conformers with respect to directions of the carbonyl group in the acetyl moiety and the amino-hydrogen atom but the predominant conformer of NAA molecule is the cis-form. Phenacetin (PH) molecule which has ethoxy group in the Para-position instead of the hydroxyl group in the Para-position in PA molecule is another analogue of PA. The electron transfer energy between the drugs and the nucleic acid bases can be illustrated as cancer energy barrier. The cancer energy barriers were calculated from the DFT parameters for all the studied molecules showing the carcinogenic effect. The metabolized product N-acetylimidoquinone, m-PA, is produced in the liver from PA and PH. m-PA has higher electron affinity more than those of the nucleic acid bases indicating to the strong electronic withdrawing power from the nucleus in the human being liver cell, hence m-PA is responsible for the carcinogenic behavior of the liver cell since it has low energy barrier with guanine, 0.3 eV. Therefore the electron transfer between m-PA and guanine takes place spontaneously in the liver. From CI calculations it has been concluded that the singlet transition energies for the trans and cis conformers of PA are the same. The comparative spectral studies have been scanned for some analogues in the visible and UV regions using solvents of different polarities. The complex between PA and Zn 2+ was studied by DFT method.

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A new class of polyconjugated polymers, namely poly ( 2,5-arylidenecyclopentanone ) and poly ( 2,6-arylidenecyclohexanone ) has been obtained by condensation of cyclopentanone or cyclohexanone with terephthalaldehyde using alcoholic potassium hydroxide as a catalyst. Copolymerization of the corresponding monomers was also carried out. To characterize these polymers model compounds were prepared from cyclopentanone or cyclohexanone and benzaldehyde. The structures of the model compounds were elucidated by IR, NMR, and elemental analyses. The polymers produced were characterized by elemental analysis, IR, UV, viscometry, DSC measurements, thermogravimetric, and X-ray analyses. From the SCF-CI calculations, the 2,5-dibenzylidenecyclopentanone, as a model compound, has the trans form. Furthermore, the charge densities of this model, its anionic and cationic forms, as well as the ionization potential and the electron affinity have been calculated.

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