Electrophilic Addition in Conjugated Dienes

Learning
Objectives

At the end of this
lecture, student will be able to

• Explain the concept of resonance in conjugated dienes

• Relate ∆H and resonance to the stability of conjugated
dienes

• Explain the mechanism of electrophilic addition in
conjugated dienes

Stability
of Conjugated Dienes

• Heat of hydrogenation ∆H

• Conjugation – delocalization of electrons – resonance

Electrophilic
Addition in Conjugated Dienes

• 1,2 – addition

• 1,4 –

Mechanism
of Electrophilic Addition in Conjugated Dienes

• Step 1

• Step 2

• 1, 2 vs 1, 4-addition

Rate vs equilibrium

• Equilibrium favours 1, 4 – addition product

Summary

• Conjugated dienes are resonance stabilised due to
delocalization of π electrons

• Conjugated dienes undergoes electrophilic addition to give
1, 2 – Addition and 1,4 – addition product

• 1,2 – addition product is kinetically favoured

• 1,4 – addition product is thermodynamically favoured

• Most rapidly formed product is the kinetic product

• Most stable product is the thermodynamic product