Which of the following pairs do not constitute resonance structures ?

Explanation

(a) In resonance, the position of atoms or nuclei remains fixed, so pairs in (ii) constitude resonance. In othe pairs, the position of atoms are changing , therefore, (i),(iii), and (iv) pairs do not constitude resonance structures.
(i) They constitude functional isomerism (nitro to nitrite)
(ii) They constitude resonance structures.
(iii) They constitude tautomerism (keto and enol) and also show functional isomerism.
(iv) They constitude positional isomerism (position of double bond has changed).
(b) (i) `(C - Br)`, since `Br` is more `EN` than `H`.
(ii) `(C - O)`, since `O` is more `EN` than `N`
(iii) `(C - O)`, since `O` is more `EN` than `S`.
( c) Inductive effect is least in `(C_2 - C_3)` bond because the magnitude of inductive effect diminishes as the number of intervening bond increases.
(d) (i)
(ii) Picric acid is `2,4,6-`trinitrophenol.
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