When one structure is not sufficient (enough) to explain each and every property (chemical & physical) then, different structure has been drawn which are known as Resonating Structure (canonical structure).
All these structure contribute to the formation of Real structure, known as Resonating Hybrid.


Condition for Showing Resonance:

  • Molecule should be planer, nearly planer or a part of it is planer

Q.1 Which is planer?

C and D Because they are sp2 hybridized.

Molecule should posses’ conjugated system

Conjugated system:-

  • Continuous Unhybridized p-orbital parallel to each-other.

Types of conjugated system:-

(1) π-bind alternate to π-bond

 CH2 = CH – CH = CH2
(2) π-bond alternate to + charge
CH2=CH        –    CH2+

Resonance takes place due to delocalization of π e-

Position of the atoms remains the same; only delocalization of π e- takes place.

Note: – 

[They are net resonating structure rather they are tautomer]
Bond pair gets converted into lone pair and lone pair get converted into bond pair.

In Resonance No. of unpaired e- remains the same

(They are not resonating structure)

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