Comparison of non-empirical and semiempirical SCF MO calculations of non-substituted dihydropyridines

Results of ab initio MO calculations of the dihydropyridine molecules I-V are confronted with analogous CNDO/2 and MINDO/3 calculations. The molecular energies calculated by means of the 4-31 G base predict the 6pi-electron isomers I and II to be the most stable dihydropyridine forms in contrast to the STO-3G and CNDO/2 data preferring the 4pi-electron isomers III-V. The charge distributions calculated non-empirically and semiempirically show different characteristic features.