THE TOPOLOGY OF THE CHARGE-DISTRIBUTION AND THE ELECTRIC-FIELD GRADIENT AT THE N-NUCLEUS IN IMINES AND DI-IMIDES

A relationship between critical points that define the topology of the Laplacian of a molecular charge distribution del2rho(r), and components of the electric-field gradient (EFG) tensor at the nucleus of the two-coordinated N, obtained from an ab initio molecular-orbital calculation, was found in di-imides (R-N=N-H with R=H, F, and CN) and imines (RHC=N-H with R=H, F, CN, and CH3). The q(zz) component of the EFG was found to be determined by the position and magnitude of the nonbonded charge concentration present in the N valence shell, as defined by a maximum in - del2rho(r). The orientation of the z axis of the tensor was determined to be associated with three local maxima in - del2rho(r) present in the N valence shell while the asymmetry parameter of the tensor was found to be related to saddle points of the N valence shell located above and below the molecular plane.