Some CNDO Calculations and Structural Spectroscopic Studies of Paracetamol Complexes

Through complete neglect of differential overlap (CNDO) calculations of the electronic energy among different possible structures of paracetamol (PA) molecule, it has been concluded that its structure has C_s point group symmetry of the cis‐form in which the methyl group has a restricted free rotation around its bond with the carbon atom of the amide group. The electronic spectra of PA compound were studied in different polar and nonpolar solvents. The temperature effect on the electronic spectra confirms the presence of one conformer only. The hydrogen bonding and the orientation energies of the polar solvents were determined from the studies of mixed solvents. Complexes of PA with metal ions M(II) (Cu⁺⁺, Zn⁺⁺, or Fe⁺⁺) of ratio 2:1, respectively, were prepared, and their structure has been confirmed by elemental analysis, atomic absorption spectra, IR spectra, and ¹H‐NMR spectra. It has been concluded that the structure of the complexes has C_2h point group symmetry in which two PA molecules are chelated to any one of the metal ions Cu⁺⁺, Zn⁺⁺, and Fe⁺⁺.