The effect of metal ion bonding to amides on the character of the CN bond of the ligand molecule

The influence of various metal ions on the character of the amide CN bond has been studied by means of NMR line shape analysis of the changes in the activation energy for internal rotation about this bond. All cations investigated raise the barrier, the increase was found to be approximately linearly correlated to the inverse radii of the ions. MO SCF calculations with small gaussian basis sets have been employed for the theoretical discussion of these results. Theoretical and experimental results concerning the ion influence on the CN bond are in satisfactory agreement. The changes in the electronic structure of the amide molecule and the character of the CN bond are illustrated using localized orbitals and electron density maps.