[en] We have carried out the RINDO/S-CI calculations of ethylene, formic acid and formamide. Ionization potentials, S→S and S→T transition energies with T-S splittings and charge distributions of the molecules are presented in this paper. The results are compared with those obtained by the RCNDO-CI method and with the experiment. It has been observed that the RINDO/S method avoids intermingling of σ and π interactions while the other semi-emipirical calculations are generally associated with such type of intermingling. In addition the S→T splittings are better described by the RINDO/S method. The RCNDO method fails completely to account for T-S splittings of n→πsup(*) transition since it ignores corresponding exchange integrals, Ksub(n) πsup(*). (author)