Benzenediazonium Ion. Generality, Consistency, and Preferability of the Electron Density Based Dative Bonding Model
The potential energy surface of benzenediazonium ion 1 has been examined with RHF, DFT, and MP2 theory, and energies also were determined up to the level QCISD(T)hMP2. The previously accepted potential energy surface characteristics are revised. The nature of the C-N bonding in 1 was studied to establish the generality of the electron density based dative bonding model for diazonium ions, to test its consistency with experimental properties, and to argue for its preferability over purely formal bonding models. The analyses show that for 1, as for aliphatic diazonium ions, it is the hydrocarbon fragment and not the N2 group that carries most of the positive charge. Compelling evidence is provided for the synergistic interplay between σ-dative C←N2 and π-back-dative C→N2 bonding. The analysis of the noble gas systems Ph-E+ (E = He, Ne, Ar) corroborates the importance of the internal polarization within N2 and of the lone pair hybridization for dative bond formation. Experimental properties of 1 including its structural characteristics, the diazonio function's substituent constant and the opposing sign dual substituent parameter reaction constants for dediazoniations and automerizations, its reactivities toward nucleophiles and electrophiles, and its 13C and 15N NMR chemical shifts show no conflict but are fully compatible with the dative bonding model. The dative bond descriptions R+←N≡N or R+⇄N≡N are clearly preferable over the commonly used Lewis-Kekule structures because they represent moee closely the actual electron density distribution.
R. Glaser and C. J. Horan, "Benzenediazonium Ion. Generality, Consistency, and Preferability of the Electron Density Based Dative Bonding Model," Journal of Organic Chemistry, vol. 60, no. 23, pp. 7518-7528, American Chemical Society (ACS), Nov 1995.
The definitive version is available at https://doi.org/10.1021/jo00128a026
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