Abstract The geometry relaxation effects accompanying the internal rotation in formamide are investigated using the selfconsistent MINDO force field procedure 1. The results of test calculations of H2O2 are also briefly summarized. The relaxation appears to be necessary for the barrier to the NH2 in version in formamide to be obtained. The calculated fully optimized equilibrium geometries of CHONH2 and H2O2 are in good agreement with experiment. However, during the rotation geo metry variations appear to be quite large. Application to formamide shows that torsion and in version are strongly coupled. The nature of the barriers calculated is analyzed in terms of the MINDO energy partitioning. Finally, it is shown that the frozen-frame variations of the charges on atoms and dipole moment of formamide, are strongly affected by the geometry optimization during rotation.
