Ab initio Hartree-Fock (HF) calculations for cyclopropane adsorbed on a Cu-cluster reveal that the so-called M*-resonance seen in X-ray absorption (NEXAFS)-spectra for saturated hydrocarbons adsorbed on metal surfaces is due to a strong electronic mixing between the metal and the molecule. Since this type of chemical interaction is unexpected and has not been observed previously the different types of interactions were carefully analyzed. In addition to the importance of correlation effects the results reveal that a small but significant interaction is due to a charge-donation from the metal states to the molecule, most likely to states of Rydberg character.