Give the stability of the following resonance structures
(a) `H_(2)C = overset(o+)N =overset(Θ)C`
(b) `H_(2)overset(o+)C -N =overset(Θ)N`
(c ) `H_(2)overset(Θ)C -overset(o+)N -= N`
(d) `H_(2) overset(Θ)C - N = overset(o+)N` .

Explanation

(i) The lesser the charge separation, the more stable the resonating structure. `(I)` and `(III)` have less charge separation. But in `(III)`, charge is on electropositive `C` atom. Therefore, `(I)` is more stable than `(III)`. Since both have six convalent bonds, so `(I)` more stable than `(III) (I gt III)`.
(ii) Both `(II)` and `(IV)` have five convalent bonds, but `(II)` is more stable than `(IV)` because in `(II)` positive charge is on electropositive `C` atom and negative charge is on `EN` (electronegative) `N` atom, whereas in `(IV)` its is reversed.
Therefore , `II gt IV`
So, the stability order is : `I gt III gt II gt IV`.