Correlation of 13C and 15N nuclear magnetic resonance chemical shifts with polarographic reduction potentials of para-substituted benzenediazonium salts and their electronic structures

Carbon-13 and nitrogen-15 nmr chemical shifts of benzenediazonium salt and its para-substituted derivatives have been measured in sulfolane solutions. The chemcial shifts of 13C1 correlate linearly with the polarographic half-wave potentials. This relation indicates the linear increase of electron densities at C1 with the increase of electron-donating power of the substituents. Non-linear relationships between 15N shifts of both nitrogen nuclei and the half-wave potentials were partly attributed to the second-order paramagnetic contributions to the 15N shifts. This contribution is approximately proportional to the inverse of the uv absorption frequencies. Overall results suggest that in the ground state resonance structures of the benzenediazonium salts, the rehybridization of the C1—N1 bond is very unlikely and this bond remains as a single bond.