1. The document discusses various electrophilic addition reactions that can occur with alkenes, including addition of bromine, hydrogen bromide, water, peroxyacids to form epoxides, borane to form alcohols, mercury acetate for oxymercuration-demercuration, and ozone for ozonolysis. 2. Key aspects of the reactions are discussed, including reaction mechanisms and products obtained via Markovnikov or anti-Markovnikov addition. 3. Examples are provided for many of the addition reactions to illustrate how different functional groups are formed depending on the reagents used.

1. Electrophilic Addition to Alkene
Dr. Firoz Khan
Assistant ProfessorAssistant Professor
AIKTC, School of Pharmacy,
Panvel, Navi Mumbai, India.
https://scholar.google.co.in/citations?user=FkGHPWQAAAAJ&hl=en

2. Contents
1. Addition of bromine
2. HBr (in presence and absence of peroxide)
3. Reaction with N-bromo succinimide.
4. Water
5. Oxidation of alkenes to epoxide
6. Hydroboration-oxidation
5. Oxidation of alkenes to epoxide
6. Hydroboration-oxidation
7. Dimerization
8. Oxymercuration-demercuration
9. Ozonolysis
10.Periodate cleavage

4. Addition of bromine (Halogens)
Reaction
Mechanism

5. Formation of Halohydrin
Mechanism
Example

6. Addition of HBr (Absence of peroxide)

7. Markovnikov’s rule
Addition of hydrogen to an unsymmetrical alkene occurs at those
carbon atoms with maximum number of hydrogen atoms.
Such an addition leads to a stable carbocation.

8. Addition of HBr (Presence of peroxide)
In the presence of peroxides, HBr adds to an alkene to
form the “anti-Markovnikov” product.
Peroxides produce free radicals.
Free-Radical Initiation
Propagation Steps

9. Addition of HBr to alkene

10. Reaction with N –Bromosuccinimide (NBS)

12. Addition of Water
The Markovnikov addition of water to the double bond
forms an alcohol.
Uses dilute solutions of H2SO4 or H3PO4 to drive equilibrium
toward hydration.

13. Mechanism

14. Orientation

15. Epoxidation
Alkene reacts with a peroxyacid to form an epoxide
(also called oxirane).
The usual reagent is peroxybenzoic acid.
The peroxyacid and the alkene react with each other
in a one-step reaction to produce the epoxide and a
molecule of acid.
The most common peroxyacid used is meta-
chloroperoxybenzoic acid (m-CPBA).

16. Mechanism
Example
Stereospecific

17. More substituted alkenes
epoxidize faster
One equivalent of peroxyacid
epoxidize one alkene
Ring Opening

18. Anti-addition will
be formed.

19. Hydroboration-Oxidation of Alkenes
One Borane reacts with three alkenes to form trialkyl borane which on
further oxidation with H2O2 form three molecules of alcohol.

20. The reaction adds BH3 across the double bond with anti-
Markovnikov orientation and forms the alcohol.

21. OH
HBH3
H2O2
CH
CH3
H C
CH3
Examples for Hydroboratio-oxidation reaction
CH3
HH
H3C
BH3
H2O2
CH3
OHH
H3C
BH3
H2O2
OH
H

22. DimerizationDimerization

23. Oxymercuration-demercuration
Reagent is mercury(II) acetate, which dissociates to
form +Hg(OAc).form +Hg(OAc).
+Hg(OAc) is the electrophile that adds to the pi bond.
The intermediate is a three-membered ring called the
mercurinium ion.
Overall the addition of water follows Markovnikov’s
rule.

24. Mechanism of Oxymercuration-demercuration

25. Example

26. Ozonolysis
Ozone will oxidatively cleave (break) the double bond to
produce aldehydes and ketones.
A second step of the ozonolysis is the reduction of the
intermediate by zinc or dimethyl sulfide.

27. Mechanism
The ozone adds to the double bond, forming a five-membered ring
intermediate called molozonide, which rearranges to form the
ozonide.
The ozonide is not isolated, but is immediately reduced by a mild
reducing agent, such as zinc or dimethyl sulfide, to give the
aldehydes and ketones as the main products.

28. Ozonolysis can be used to generate not only aldehydes, but also
other functional groups.
Completing the reaction with oxidizing agents such as H2O2 will
give carboxylic acids, and more powerful reducing agents such as
NaBH4 will give alcohols.

29. Periodate cleavage
This can be done in two steps using OsO4 in conjunction with the
reagent sodium periodate, NaIO4/ HIO4.
The diol product forms a periodate ester, which decomposes to give
two molecules of aldehyde or ketone.

30. Mechanism

31. When KMnO4 is used instead of OsO4, the ketone
will remain ketone, aldehyde will oxidise to
carboxylic acid and formaldehyde will form CO2.