Class 11 Chemistry Notes General Organic Chemistry - AglaSem
  1. Hypothetical structure exist on paper
  2. The energy difference between different resonating structures is very small.
  3. All Resonating Structure contribute towards the formation of resonance hybrid.
    (Their contribution may different)
  4. A single Resonating Structure can’t explain each and every property of that particular compound

Drawing Resonating Structure: –






Resonance hybrid: –

  • It is a real structure which explains all the properties of a compound; formed by the contribution of different resonating structure, Hybrid is a single diagram way to explain everything.
 Resonance Energy: –
It is the difference between theoretical value of Heat of Hydrogenation and experimental value of Heat of Hydrogenation or we can say that
It is the difference between most stable Resonating Structure and most stable Resonating Hybrid.
  • More the resonance energy, more stable will be the molecule.
  • Cyclohexane is thermodynamically more stable than benzene; even though resonance energy of benzene is more.
  • Resonance energy is an absolute term.
Contribution of Different Resonating Structure towards Resonance Hybrid
(1) Non- polar Resonating Structure contribute more than polar Resonating Structure
(a) CH2 = CH – CH = CH2
(b) 40
(c) 41
a> b = c stability
(2) Polar R.S. With complete octet will contribute more as compared with the one with incomplete octet

(3) In polar Resonating Structure The negative charge should be on more electronegative atom and positive charge should be more electropositive atom



(4) Compound with more covalent bond will contribute more towards resonating hybrid.

(5) Unlike charges should be closer to each other whereas like charges should be isolated.

(6) Extended conjugation contributes more than cross conjugation.

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