Fig. 7. (top) Natural population analysis gives the anion charge which is 75% on the nitrogen atom, and MO analysis gives that both the HOMO and the LUMO are centered on the carbon. In covalent systems and/or systems with significant backbonding, binding through the carbon is expected based on the MOs; however, very polar systems may bind to the nitrogen of cyanide. (bottom) Plot of the enthalpy difference57–61 between the cyanide (e.g., HCN) and isocyanide (e.g., HNC) structures vs. the percentage of ionic bonding from Natural Resonance Theory (NRT).62.
