THE ELECTRIC-FIELD GRADIENT AT THE N-NUCLEI AND THE TOPOLOGY OF THE CHARGE-DISTRIBUTION IN THE PROTONATION OF UREA

A relationship between some of the critical points of the Laplacian of the charge density of the N valence shell and the electric field gradient (EFG) present at the nucleus of the three-coordinated N atom was found for the amine group in urea and some of its adducts and salts. The qzz component of the EFG was shown to be determined by two nonbonded charge distribution local maxima, present below and above the molecular plane in the N valence shell. The asymmetry parameter of the EFG was found to be related also to this nonbonded charge concentration. The effect of increasing protonation in urea produced a decrease in the N nonbonded charge concentrations, an increase in bonded concentration along the N-H bond directions and complex fluctuations in the bonded concentration along the N-C bond. The combined effect of the additional H bonds involving the amine group of urea and of the O atom protonation on the N valence shell concentration, is also discussed. © 1994 American Institute of Physics.