1. WELCOME

2. ADDITION REACTION
RAHUL B S
M PHARM PART 1

3. CONTENTS
Introduction
Types of addition reaction
Orientation and reactivity
Reactions
References

4. INTRODUCTION
Addition reaction is defined as that reaction in which
all the reagent atoms are added to the reactant and thus
the product contains all the atoms of the reactant as well
as that of the reagent.
Characteristic feature of unsaturated compounds

5. Types of addition reaction
Electrophilic addition
Nucleophilic addition
Free radical addition
Addition to conjugated system

6. ELECTROPHILIC ADDITION
Step 1 H y
slow +
+ C C H
H2C CH2 + y
H H
Step 2
H y w y
+ -
C C H
+ w H C C H
H H H H

7. The second step is similar to SN1 mechanism
Not all additions follow the simple mechanism
Eg; -
Br
Br Br
+
+ Br Br Br
C C
H2C CH2 H2C CH2
H H

8. STEREO CHEMISTRY
Three possibilities.
• Y and W enter on same side of the plane, addition is stereospecific
and syn
• May enter on the opposite sides, stereospecific anti addition
And may be Not stereospecific
• YW is added to cis and trans of an olefin ABC=CBA Cis olefin is an eg;
If the addition is syn the product will be erythro
If the addition is anti the product is threo

9. Erythro
y w w
y
A A A
B
C C
A B
B B
w
y
y
w A
A A
B
C C
A B
B B
Threo
y
A B
y
A A
w
C C A B
B w
B
w
A B
A A w
C C y
A B
B y B

10. If Y=W (Br2 ) the erythro pair is meso compound.
STEREOCHEMISTRY OF HX
• The stereochemistry of HX is varied
• Treatment of 1,2, dimethyl cyclohexene with HBr gave predominent
antiaddition
H3C Br
CH3
HBr
H3C
CH3
While addition of water to 1,2- dimethyl cyclohexene gave equal amount
of the cis and trans alcohols.
H3C H3C CH3
CH3 OH
H2O
H3C HO
CH3
+

11. NUCLEOPHILIC ADDITION
step 1
y
slow -
H C C H
H2C CH2 + y-
H H
step 2
y y
w
-
H C C H + w
+ H C C H
H H H H

12. Addition of HY to a substrate of the form –C=C-Z, where Z =
CHO,COR,COOR,CONH2,SOR,SO2R etc.
H y y
- - -
y + C C C O [ H C C C O H C C C O ]
H H H H H H H H H
y y H
HY
H C C C OH H C C C O
H H H H H H
Protonation occur at oxygen
The mechanism is 1,4 nucleophillic addition.

13. When Z = CN or CO
Y- attack to the carbon, similar to the above
Mechanism may be 1,2 or 1,4 addition .
Y- never attack at 3 position
y
y
- -
H H C C C O
C C C O
H H H H H
H

14. An important substrate of this type is acrylonitrile and 1,4 addition to is
called cyanoethylation,because the Y is cyanoethylated
H2C CH C N + HY y CH2 CH2 C N

15. STEREO CHEMISTRY
•Nucleophillic addition is carbanion mechanism
•Addition should be nonstereospic and stereoselective.
Eg ; E and Z from of an olefin ABC=CDE
-
- y D C
A D Y
E
C C C
A B
B E
E -
y C
A E Y-
C C C D
A B
B D

16. Eg ; addition of HCN, addition of alcohols
Addition of HCN
Ba(CN)2
HC CH + HC N H2C CH C N
acrylonitrile
Addition of alcohols
KOH
HC CH + H3C OH H2C CH O CH3
vinyle methyl ether

17. FREE RADICAL ADDITION
hv or spontaneous
YW y*
dissociation + W*
step 1
y
H2C CH2 + y* H C CH2
H
step 2
W y
y
y*
H C CH2 + YW H C C H +
H H H

18. When free radicals are added to 1,5 or 1,6 dienes, the initially formed
radical can add intramolecularly to the other bond leading to a cyclic
product.
Eg;
y CH2 CH2 Y CH CH2
H2C CH2 HC
CH2 HC C
CH HC
+ y*
CH2 CH2 CH2 CH2 + YW
CH2 CH2 CH2 CH2
CH2
Y CH2 CH2 W
HC HC
CH2 CH2
CH2
It should be non stereospecific, may stereoselective,
Not all free radical additions are stereoselective

19. For many radicals step 1 is reversible.
Causes cis – trans isomerization.
1 2 1 4
R R R R 1
4
1 R
R 2 y* R
R
y C C y C C
4
3 4 rotation 3 2 R
3 R
2
R
3 R R R R R
CYCLIC MECHANISMS
•Initial attack is not at one carbon
•Both carbon are attacked simultaneously
y w
y w
H C C H H3C C C CH3
CH3 CH3
H H

20. ADDITION TO CONJUGATED SYSTEM
Electrophillic addition on a compound with two double bonds in
conjugation 1,2 addition product is often obtained, but in most
cases there is also a 1,4 addition product often in larger yield.
y w y w
CH yw
H2C CH CH2
+ H C CH CH CH2 + H C CH CH C CH3
H H CH3
y y
H2C CH CH CH2
+ y
+
[ H C C
+
CH CH2 H C CH CH
+
C H ]
H H H H

21. ORIENTATION AND REACTIVITY
Electron donating groups increase the reactivity of a double bond
towards electrophilic addition.
Electron withdrawing groups decrease it.
The reactivity toward electrophilic addition of a group of olefins increased
in the order.
CCl3CH=CH < Cl2CHCH=CH < ClCH2CH=CH <CH3CH2=CH2
2 2 2
Simple olefins do not react by the nucleophilic mechanism
Compounds that have a double bond conjugated with a Z-group always
react by a nucleophilic mechanism
Z= NO2,COAr,CHO,COR,CN,COOR,CONH
2,CONHR

22. Electron withdrawing groups enhance nucleophilic addition and inhibit
electophilic addition
In compounds containing both double and triple bonds ,bromine,an
electrophilic reagents, always adds to the double bond
Bridged intermediates reacts faster with double than with triple bonds
The presence of electron withdrawing groups lowers the alkene/alkyne
rate ratio
Triple bonds are more susceptible to nucleophilic & less to electrophilic
attack than double bonds
Alkyl groups in general increases the rates of electrophilic addition
In free radical addition the main effect seems to be steric
Stability order of the free radical intermediates 30 > 20 > 10

23. STEREOCHEMICAL ORIENTATION
The syn addition of an unsymmetrical cyclic olefin, the two groups can
come in from the more hinderd face or from the less hinderd face of the
double bond.
CH3 O CH3
CH3 peroxylauric
+
acid H H
H
O
76% 24%
In anti additon the initial attack by the electrophile is from less hindered
face.

24. Addition to cyclopropane rings
Addition to cyclopropane ring results in the opening of 3 membered
ring.
H3C CH2 CH2 Br
H2C
CH2
CH2
+ HBr
F O
CH2 CH Bu
H2C CH Bu
+ F C C H3C CH2
F
F OH F
O C C
OAc
O F
+ Pb(oAc) 4
OAc
Addition of cyclopropane involves electrophillic addition.
Substituted cyclopropane follow markonikov’s rule.
CH3 CH3
CH2
HC C CH3 + HX H3C CH C X
H3C CH3
CH3

25. REACTIONS
Addition of hydrogen halides
Alkenes reacts with hydrogen halides form alkyl halides
Order of reactivity
HI >HBr>H Cl >HF
H2C CH2 + HX H3C CH2 X
If olefin is symmetrical alkyl halide is formed.
If it is unsymmetrical two different alky halides are possible.

26. H3C CH2 CH2 anti markonikof rule
Br
n - propyle bromide
HBr
H3C CH CH2
++
propylene
H3C CH CH3
markonikof rule
Br
iso propyle bromide

27. MARKOWNIKOFF RULE
The positive portion of the reagent goes to the side of the double or
triple bond that has more number of hydrogen atom.
The negative (or more negative) part of unsymmetrical addendum
attaches to that carbon atom of the double bond which bears the least
number of hydrogen atoms.
MECHANISM
H X H X
+ +
H3C CH CH2 H3C CH CH2 H3C CH 2 CH2
X
H3C CH+ CH3
:X-
H3C CH CH3

28. The peroxide effect (anti-Markownikoff’s addition)
Addition of hydrogen bromide to propene in presence of air, peroxide or light
yields predominantly n-bromo pentane i.e, the reagent adds on the olefin in a
manner contrary to Markownikoff’s rule.
H3C CH2 CH2
Br anti markonikof rule
n - propyle bromide
HBr
H3C CH CH2
++
propylene
H3C CH CH3
Br markonikof rule
iso propyle bromide

29. Dissociation
RO:OR 2OR
alkoxy radical
RO* + HBr ROH + Br
Bromine free radical
H3C CH2 CH2 Br
Br + H2C CH CH3
Propene
Br
H3C CH CH3 +
Br
HCl and HI do not give peroxide effect.
HCl bond is stronger than H-Br bond it is not break by free
radicals easily.
HI is weaker than H-Br it is broken easily but the Iodine atoms
combine readily and yield iodine molecule.

30. REFERENCES
Jerry March , Advanced Organic Chemistry,Wiley Student Edition, 734
O.P. Agarwal, Organic Chemistry, Goel Publishing House, 409
Morrison Boyd , Organic Chemistry, Prentice Hall of India Private Limited
, 317