An ab initio SCF-MO study of the aromaticity of some cyclic compounds

The application of three different procedures (PMO Method, the Orbital Energy Method, and the Total Energy Method) to the computation of the ? delocalization energies of a series of cyclic compounds (cyclopentadiene, furan, pyrrole, thiophene, and benzene) is described. The study was performed in the framework of ab initio SCF-MO computations at the STO-3G level. It was found that, while the PMO Method and the Orbital Energy Method provide values of the delocalization energy which correlate very well with the experimental resonance energies, the Total Energy Method needs to be "appropriately" corrected. The correction consists of subtracting the energy effect of the corresponding acyclic species from the energy effect of the cyclic compound. It was also found that the use of a quantitative PMO analysis provides information on the role of the various orbital interaction(s) which are responsible for the extent of aromaticity in these compounds. © 1988.