Abstract:
Semi-empirical molecular orbital methods have been employed to predict the effect of nitration of benzene, aniline, chlorobenzene, iodobenzene, and toluene as simple aromatic systems. The effect of substitution at ortho, meta, or para positions on enthalpies of formation, ionization energies, and dipole moments have been calculated employing AM1 and PM3 methods in HyperChem.™ Bond lengths, bond angles and frequencies of infrared absorption were calculated using the PM3 method. The calculated values have been compared with their experimental counterparts.
Both the AM1 and PM3 methods provide useful accuracy. However, the AM1 method gives better results than PM3 for the study of aromatic compounds containing carbon, hydrogen, nitrogen, and oxygen. The PM3 calculations of infrared frequencies give random errors, in contrast to ab initio calculations, which give results that are systematically too high.
