SUBSTITUENT EFFECTS AND THE CHARGE TOPOLOGY IN NITRILES AND CYANIDES

In order to study the substituent effects and the bonding of the C = N group, a SCF 4-31G** ab initio calculation was undertaken for the C = N- ion, for nitriles with R = H, F, HO, FO, H3C, HC = C, NH2, O = N, N3, C = N, the E and Z form of iminoacetonitrile and for cyanides with R = Li, HBe, and B. The electron density rho(r) was analyzed by means of the topological theory of atoms in molecules. The surfaces of zero-flux in del-rho(r) showed that the C valence density of the target fragment absorbed most of the changes, while the N was only slightly perturbed by the R-C bond formation. A correlation was found between the position of the bond critical point and the electronegativity of R for R-C in nitriles but not for the C = N bond. This difference was explained by the changes in the strength of the substituent fields acting on both bonds. The del 2-rho(r) distribution in the C = N group for the different substituents and counterions showed that all the bonded and nonbonded local concentrations present in the C and N valence shells were affected in a complex way by the bond formation.