14N Nuclear Quadrupole Resonances of the Molecular Complexes of Urea

The 14N nuclear quadrupole resonance (NQR) was studied on three kinds of molecular complexes of urea, such as the urea–hydrogen peroxide complex (H2O2 complex), the urea–sodium chloride–water complex (NaCl complex), and the urea–sodium bromide–water complex (NaBr complex). The 14N quadrupole coupling constants and asymmetry parameters are as follows: |e2Qq⁄h|=3493.8 kHz and η=0.3456 for the H2O2 complex; |e2·Qq⁄h|=3597 kHz and η=0.293 for the NaCl complex, and |e2Qq⁄h|=3636.7 kHz and η=0.2778 for the NaBr complex. From the temperature dependence of the resonance frequencies, it is considered that the hydrogen bonds in the H2O2 complex are stronger than those in the NaCl complex. The electron densities at nitrogen atoms in these complexes were derived from the corresponding NQR parameters, and were compared with those in urea.