Delocalization of lone pairs

The delocalization of lone pair electrons on NH group to an adjacent N=N bond was suggested by some calculations [97] to be appreciable in triazene 12 and 2-tetrazene 13. The N-N single bond is shorter than the isolated N-N single bond in NH NH. The N=N bond is longer than in NH=NH. The n-n conjngation stabilizes hydronitrogens. 

The hypothesized delocalization of lone pair electrons in the above silicon compounds is supported by the lowered basicity of the silyl compounds as compared to the corresponding carbon compounds. This reduced basicity is contrary to that expected on the basis of electronegativity effects operating through the a system since silicon is less electronegative than carbon. It is consistent with an internal Lewis acid-base interaction between the nitrogen and oxygen lone pairs and empty acceptor d orbitals on the silicon. Experimentally this reduced basicity is shown by the absence of disiioxane adducts with BF3 and BO ... 

The resonance interaction shown for bicarbonate ion is more important than an alternative one involving delocalization of lone-pair electrons in the OH group. 

Aniline is stabilized by delocalization of lone pair into tt system of ring, decreasing the electron density at nitrogen. 

With respect to the 2D analysis, JP R clearly described for the first time the simultaneous hyperconjugative effects deriving from delocalization of lone-pair density on each oxygen atom into the (t co antibonding orbitals associated with their counterpart oxygens. While they did not refer to this by name, in essence this was the first demonstration of simultaneous anomeric and exo-anomeric effects. 

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