Elimination reactions are exact reverse of addition reactions.

1. ELIMINATION REACTIONS
PRESENTED BY:
•Gandham Malasree
•M Pharmacy
•Regd no: 620209502002
•Dept of Pharmaceutical Chemistry
•AU college of Pharmaceutical sciences

2. ELIMINATION REACTIONS:
• Elimination reactions are exact reverse of addition reactions.
• Its is defined as removal of atom or group of atoms from the adjacent carbon of a
molecule and this leads to the formation of multiple bonds either double bond or
triple bond depending on how many atoms are removing.
• Elimination reactions are endothermic reactions i.e,. These reactions takes place in the
presence of heat.
Elimination reactions
Alpha elimination reactions Beta elimination reactions

3. 1,1-Elimination or α-Elimination:
It is an elimination reaction in which an organic compound loses two ligands from
the same atom .
Alc.KOH

4. β-Elimination (beta-elimination)
E1 E2 E1cb

5. Eg; Dehydrohalogenation Of Alkyl Halides
this reaction undergoes two mechanisms i.e., E1 & E2

6. E2 MECHANISM:
 It is a bimolecular reaction.
 It is a single step process.
 It follows second order kkinetics.
 Rate α [ substrate ] [ Nucleophile].
 1o alkyl halides undergo E2 Mechanism
 E.g., n-propyl bromide

7. E1 MECHANISM:
 It is an unimolecular reaction.
 It is a two step process.
 It follows first order kkinetics.
 Rate α [ substrate ].
 3oalkyl halides undergo E1 Mechanism
 E.g., 3o butyl bromide

8. Step 1: Formation of carbocation by ionization

9. Step 2: Elimination of proton

10. E1cb reaction :
 It is a unimolecular reaction.
 It is a two step process , it forms carbanion as intermediate which is conjugate base of
starting material.
 It follows second order kinetics.
 Rate α [ substrate ] [ Nucleophile].
 It should have a poor leaving group
 Beta hydrogen is highly acidic in nature.
 It follows Hoffmann rule.
General reaction:

11. MECHANISM:
Step 1: Formation of carabanion by deprotonation
Step 2: Removal of halide

12. Type E1 E2 E1cb
Intermediate/
transition state
Carbocation No Intermediate Carbanion
Reactivity order 3∘>2∘>1∘ 3∘>2∘>1∘ 3∘>2∘>1∘
Regioselectivity Saytzeffs Rule Saytzeffs Rule And
Hoffman Rule
Hoffman Rule
Reagent Weak Base
Polar Protic Solvent
Strong Base Aprotic
Solvent
Stereochemistry Non –
Stereospecific
Racemization
Stereospecific
Anti- Elimination