electrophilic addition reactions

1. GENERAL MECHANISM (When electrophile does not have lone pair like etc.)
NOTE:
1. 1st step is the rate determining step (rds) of this reaction.
2. Carbocation intermediate is formed. Rerrangement may be possible.
3. Rate of EAR Nucleophilicity of alkene
stability of carbocation formed.
ELECTROPHILIC ADDITION REACTION (EAR)

2. (A) (B) (C)
NOTE: Alkene is more reactive than alkyne towards EAR.
ELECTROPHILIC ADDITION REACTION (EAR)
(A) (B)

3. Observed in those reactions in which carbocation is formed as intermediate.
Less stable carbocation rearranges itself to more stable carbocation by shifting of
via formation of a 3 membered cyclic transition state.
Transition state
Rearrangement can be ‘n’ times but each time by 1,2-shift and the formed
carbocation should be more stable either through hyperconjugation
or resonance.
REARRANGEMENT IN CARBOCATION

4. 
Ph – C – CH2
Ph
Ph
REARRANGEMENT IN CARBOCATION

5. REARRANGEMENT IN CARBOCATION

6. REARRANGEMENT IN CARBOCATION

7. REARRANGEMENT IN CARBOCATION

8. REARRANGEMENT IN CARBOCATION

9. REARRANGEMENT IN CARBOCATION

10. Note: never rearranges.
+ve charge on pi bond never rearrange.
REARRANGEMENT IN CARBOCATION

11. RING EXPANSION
If there is next to a 4 or 5 membered ring then ring expansion takes place.
4 membered ring converts into a 5 membered ring and 5 membered ring converts into
a 6 membered ring
REARRANGEMENT IN CARBOCATION

12. REARRANGEMENT IN CARBOCATION

13. Cyclopropyl methyl
carbocation
RING CONTRACTION
REARRANGEMENT IN CARBOCATION

14. CHEMICAL REACTIONS OF ALKENE/ALKYNE

15. CHEMICAL REACTIONS OF ALKENE/ALKYNE

16. STEREOCHEMISTRY OF REACTION
When a reactant that does not have a chiral centre undergoes an addition reaction
and forms a product with one chiral centre then racemic mixture is formed.
CHEMICAL REACTIONS OF ALKENE/ALKYNE

17. 1. Reaction with CONC. H-X ( HALOGEN ACID ) (Hydrohalogenation)
Mechanism:
NOTE:
1.Carbocation intermediate is formed.Rearrangement may be possible.
2.Rate of reaction- HI > HBr > HCl > HF
EAR or CHEMICAL REACTIONS OF ALKENE/ALKYNE

18. Markovnikov’s rule:
The rule states that negative part of the reagent gets attached to that unsaturated carbon
which possesses lesser number of hydrogen atoms.
NOTE:
1.Markovnikov’s rule is not applicable if double bonded carbon atom have same
number of hydrogen atoms..
2.Not applicable in the cases where double bonded carbon is directly attached
to strong electron withdrawing group.
Note: Always make more stable carbocation.
CHEMICAL REACTIONS OF ALKENE/ALKYNE

19. REACTIONS (E.A.R.)
Q.
Q.

20. Q.
Q : Total products formed on addition of H-Br to But-1-ene?
(A) 1 (B) 2 (C) 3 (D) 4

21. Q.