Bimolecular Elimination Reaction

Contents

• Elimination reaction

• Dehydrohalogenation

• E2 reaction

• Mechanism

• Reactivity of E2 reaction

• Orientation of E2 reaction

• Ozonolysis

Learning
Objectives

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

• Explain kinetics and mechanism of E2 reaction

• Outline reactivity and orientation in E2 reaction

Elimination
Reaction

• Definition

• Example

– Dehydrohalogenation of alkyl halide

– 1, 2 – elimination or β elimination

• Mechanism

• E1 – Elimination unimolecular

• E2 – Elimination bimolecular

E2 Reaction

• Definition

– Bimolecular elimination reaction

• Example

• Kinetics

– 2nd order kinetics

– Rate = k [alkyl halide] [base]

• Mechanism

• Orientation

– Saytzeff rule

“The more substituted alkene product is obtained when a
proton is removed from the β -carbon that is bonded to the fewest hydrogens”

– Saytzeff rule

– Ease of formation of alkenes

– Stability of alkenes

• Reactivity

Order of reactivity of alkyl halides towards E2

Ozonolysis

• Ozonolysis is an organic reaction where the unsaturated
bonds of alkenes and alkynes are cleaved with ozone

• Alkenes and alkynes form organic compounds in which the
multiple carbon–carbon bond has been replaced by a carbonyl group

Summary

 • Alkyl halides
undergo β elimination reactions and the product is alkene

• Dehydrohalogenation involves removal of a proton and a
halide ion

• E2 reaction is bimolecular elimination reaction

• E2 reaction mechanism takes place in 1 step

• More stable alkene is the major product which is given by
Saytzeff rule

• Tertiary alkyl halides readily undergo E2 reaction