Preparation and reactions of alkane, alkene, conjugated diene, uses of paraffins, electrophilic addition reaction, free radical addition reaction, markovnikov rule, antimarkovnikov rule, stability of alkenes, conjugated dienes, E1 and E2 reaction and mechanism.

1. Alkanes and alkenes
Mr. Mote G.D.
ADCBP, Ashta Dist: Sangli
Maharashtra

2. Alkanes
• alkanes are the simplest class of organic compounds. They are made of
carbon and hydrogen atoms only and contain two types of bonds, carbon-
hydrogen (C—H) and carbon-carbon (C—C) single covalent bonds. They do
not have functional groups.
• Alkanes form a homologous series with the general formula CnH2n+2,
where n is the number of carbon atoms in the molecule The first member
of the family has the molecular formula CH4, (n = I) and is commonly
known as methane and the second member with molecular formula C2H6,
(n=2) is called ethane.
• These compounds are also known as the Saturated hydrocarbons.
• These hydrocarbons are relatively unreactive under ordinary laboratory
conditions, but they can be forced to undergo reactions by drastic
treatment. It is for this reason that they were named Paraffins (Latin
parum affinis =little activity).
C
H
H H
H
Methane
C C
H
H
H
H
H
H
ethane
2Mr. Mote G.D

3. SP3 hybridization of alkanes
• According modern orbital theory carbon has electronic
configuration.
• C (ground state) 1S2 2s2 2pX
1. 2pY
1 2pZ°,
• C (excited state) 1S2 2s1 2pX
1. 2pY
1 2pZ
1,
• One 2s and three 2p orbital gives 4 new sp3 orbitals
• The four new sp3 orbitals are arranged in space in such a way that
their axes are directed towards the corners of a regular
tetrahedron.
• In the formation of a methane molecule, the sp3 orbitals overlap
with 1s orbitals of four hydrogen atoms to form four s-sp3 sigma
bonds.
• In ethane molecule, sp3 orbital of one carbon overlaps with sp3
orbital of the other carbon, the remaining three sp3 orbitals of each
of the two carbons overlap with the is 1s orbitals of H. atoms to
form s-sp3 sigma bonds. 3Mr. Mote G.D

4. SP3 hybridization of alkanes
C H
H
H
H
109.5°
1.09 A
C C
H
H
H
H
HH
109.5°
1.54 A1.10 A
4Mr. Mote G.D

5. Alkenes
• Alkenes are hydrocarbon that contains a carbon-carbon
double bond(C=C) in their molecule.
• Molecular formula CnH2n(n= number of carbon atoms)
• Alkenes are commonly known as olefins.
H2C CH2
ethylene
(ethene)
H2C CH CH2 CH3
1-Butene
H3C C
H
C
H
CH3
2-butene
5Mr. Mote G.D

6. SP2 hybridization
• In ethylene the carbon atoms are sp2 hybridized, they are
attached to each other by a σ bond and a π bond.
• The σ bond results from overlap of one sp2 hybrid orbital from
one with sp2 hybrid orbital of another carbon.
• The π bond is formed from overlap of unhybridized p orbital's.
• Remaining sp2 orbital's form σ bond with hydrogen atoms.
6Mr. Mote G.D

7. Method of preparation of alkanes
1. Hydrogenation of Alkenes and Alkynes
2. Reduction of alkyl halides
3. Decarboxylation of Carboxylic acids
4. Hydrolysis of Grignard Reagent
5. Action of Sodium on Alkyl haIides; Wurtz
Reaction.
6. Corey-House alkane synthesis
7. Electrolysis of salts of Carboxylic acids;Kolbe's
method
7Mr. Mote G.D

8. 1. Hydrogenation of alkene and alkyne
• Alkanes can be prepared by the catalytic hydrogenation of
unsaturated hydrocarbons in the presence of catalyst ‘Ni’ or
‘pt’ at 200⁰C to 300⁰C.
R C
H
CH2 H2
Ni

R
H2
C CH3
Alkene
Alkane
H3C C
H
CH2 H2
Ni

H3C
H2
C CH3
propene
Propane
R C CH H2
Ni

R
H2
C CH3
Alkene
Alkane
H3C C CH H2
Ni

H3C
H2
C CH3
methyl acetylene
Propane
2
2
8Mr. Mote G.D

9. 2. Reduction of alkyl halides
• Alkyl halide undergo reduction with nascent hydrogen in
presence of reducing agent like Zn/HCl to form alkanes.
R X
Alkyl halide
H2
R H HX
Alkane
Zn/HCl
H3C I
Methyl iodide
H2
H3C H HI
methane
Zn/HCl
9Mr. Mote G.D

10. 3. Decarboxylation of carboxylic acid
• When sodium salt of carboxylic acid is heated strongly with
sodalime(NaOH+CaO) to form sodium carbonate and alkane
R COONa
Sodium salt
of carboxylic acid
NaOH R H Na2CO3
Alkane

H3C COONa
Sodium acetate
NaOH H3C H Na2CO3
methane

10Mr. Mote G.D

11. 4. Hydrolysis of Grignard reagents
• Alkyl magnesium halides(Grignard reagent) are obtained by
treating alkyl halides with magnesium in anhydrous ether to
give alkanes.
RX Mg
ether
RMgX
Alkyl halide Alkyl magnesium halide
RMgX H OH R H MgX(OH)
Alkane
CH3MgI H OH 3HC H MgI(OH)
Methane
Methyl magnesium
iodide
11Mr. Mote G.D

12. 5. Wurtz synthesis
• Higher alkanes are produced by heating an alkyl halide with
sodium metal in dry ether. Two molecules of alkyl halide lose
their halogen atoms as NaX. These net result is the joining of
two alkyl group to yield symmetrical alkane having even
number of carbon atoms.
R X 2Na R X
Alkyl halide
ether
R R
Symmetrical
alkane
2NaX
H3C Br 2Na H3C Br
Methyl halide
ether
H3C CH3
ethane
2NaBr
12Mr. Mote G.D

13. 6. Corey-House alkane synthesis
• An alkyl halide is first converted to lithium dialkylcopper and
then treated with an alkyl halide to give an alkane
CH3 CH2 Cl 2Li
ether
CH3 CH2 Li LiCl
CH3 CH2 Li CuI (CH3 CH2)2CuLi LiI
(CH3 CH2)2CuLi CH3 CH2 Cl CH3 CH2 CH2 CH3
LiCl
CH3 CH2 Cu
13Mr. Mote G.D

14. 7. Kolbe's Electrolysis Method
• Alkanes are formed, on electrolysis of concentrated aqueous
solution of sodium or potassium salt of saturated mono
carboxylic acids
R COONa H2O R R CO2 NaOH H22
electrolysis 2
14Mr. Mote G.D

15. Reactions of alkanes
A. Substitution reaction
1. Halogenations
2. Nitration
3. Sulphonation
B. Thermal and catalytic reaction
1. Oxidation
2. Pyrrolysis( Cracking)
3. Isomerization
4. Aromatisation
15Mr. Mote G.D

16. 1. Halogenation
• It involves the substitution of H-atoms of alkanes by as many halogen
atoms i.e., by chlorine (chlorination) ; by bromine (bromination) by iodine
(iodination) or by fluorine (fluorination)
• Methane reacts with chlorine in the presence of ultraviolet light or at high
temperature (300°C) to yield methyl chloride or chloromethane and
hydrogen chloride.
CH4
Cl2
uv light
CH3Cl HCl
Methane chlorine methyl chloride
16Mr. Mote G.D
Cl Cl Cl Cl+hv
1. Chain initiation step
2. Chain propagation step
Cl CH3H H Cl CH3
CH3
3. Chain termination step
Cl+ CH3 Cl
+

17. 2. Nitration
• When alkane react with nitric acid at high temp(400°-500°) to
form nitro alkane
R H OH NO2
400-500°
R NO2 H2O
H3C H OH NO2
400-500°
H3C NO2 H2O
Methane
Nitro methane
17Mr. Mote G.D
HO NO2
OH NO2+hv
1. Chain initiation step
2. Chain propagation step
CH3H H CH3
CH3
3. Chain termination step
+
+
400-500
°c
NO2 CH3 NO2
OH + H H2O

18. 3. Sulphonation
• This involves the substitution of a hydrogen atom of alkane
with –SO3H.
• When pronged reaction of alkane with fuming sulphuric acid
to give alkanesulfonic acid.
R H HO SO3H R SO3H H2O

fuming
sulphuric acid
alkane
Alkanesulphonic
acid
18Mr. Mote G.D

19. 4. Combustion (oxidation)
• Combustion of alkane gives carbon dioxide and water.
• The general equation for the combustion of a hydrogen is
given below.
CxHy (x + y/4)O2
xCO2 y/2 H2O
(5 + 12/4)O2
12/2 H2O
C5H12
5CO2
heat
H= -845.2 cal/mole
pentane
19Mr. Mote G.D

20. 5. Pyrolysis (Cracking)
• The decomposition of a compound by heat is called pyrolysis.
• This process when applied to alkane is known as cracking.
• Larger alkanes are broken into a mixture lower molecular
weight alkanes, alkenes and hydrogen
CH3 CH3
500°C
absence
of air
CH2=CH2
CH4 H2
Ethane Ethene
2 2 2
Methane
20Mr. Mote G.D

21. 5. Pyrolysis (Cracking)
• Mechanism
21Mr. Mote G.D
H3C CH3
CH3
hv
1. Chain initiation step
2. Chain propagation step
CH4
3. Chain termination step
+400-500
°c
H2C CH2
2
CH3 H2C CH3H
CH3 CH2
H2
C CH2H
+

22. 6. isomerization
• Normal alkanes are converted to their branched chain isomers
in the presence of aluminium chloride and HCl
• e.g. n-butane is converted into isobutane
CH3 CH2 CH2 CH3
n-butane
AlCl3
HCl
CH3 C
H
CH3
CH3
isobutane
22Mr. Mote G.D

23. 7. Aromatatization
• Alkanes containing 6 to 10 carbon atoms are converted into
benzene and its homologues at high temp and in the presence
of a catalyst.
• e.g. n- hexane is passed over Cr2O3 supported over alumina
at 600°C to form benzene
CH3CH2CH2CH2CH2CH2CH3
n-hexane
Cr2O3-Al2O3
600°C/10 atm
4 H2
Benzene
23Mr. Mote G.D

24. Uses of paraffins
• Paraffin is widely used as fuel for jet engines and
rockets and as fuel or a fuel component for diesel and
tractor engines.
• paraffin is the most widely used heating oil in home
central heating systems in the UK and it is still used in
less developed countries as the main fuel for cooking.
• Liquid paraffin can be used as a lubricant for
machinery.
• It is commonly used to treat dry skin, constipation, and
eczema.
• Paraffin wax is also used as a water-harvesting soil
treatment to supply runoff water to dry areas, as an
adhesive and as a water-proofing agent.
24Mr. Mote G.D

25. Preparation of alkenes
1. Dehydration of alcohols.
2. Dehydrohalogenation of alkyl halides.
3. Dehalogenation of vicinal dihalides.
4. Controlled hydrogenation of alkynes.
5. Cracking of alkanes.
25Mr. Mote G.D

26. 1. Dehydration of alcohol
• When alcohol is heated in the presence of sulphuric acid to
form alkene by elimination of water
R
H
C
H
CH2
OH
H2SO4

R
H
C CH2
alkene
H3C
H
C
H
CH2
OH
H2SO4

H3C
H
C CH2
Propene
alcohol
1-
propanol
H2O
H2O
26Mr. Mote G.D

27. 2. Dehydrohalogenation of alkyl halides
• When alkyl halide is heated with alcoholic solution of sodium
hydroxide to form alkene and hydrogen halide.
R
H
C
H
CH2
x
NaOH in alcohol

R
H
C CH2
alkene
H3C
H
C
H
CH2
Cl
NaOH in alcohol

H3C
H
C CH2
Propene
alkyl halide
Propyl chloride
H2O
H2O
HX
HCl
27Mr. Mote G.D

28. 2. Dehydrohalogenation of alkyl halides
Saytzeff rule
• If the dehydrohalogenation of alkyl halide can yield more
than one alkene, according to saytzeff rule main product is
the most highly substituted alkene.
• E.g. when 2-bromo butane is heated with alcoholic KOH to
form 80% 2-butene and 20% 1-butene
28Mr. Mote G.D

29. 2. Dehydrohalogenation of alkyl halides
Saytzeff rule
C
H
C
Br
CH
H
CH3
H
H
H
2-bromo butane
KOH
KOH
C
H
C CH CH3
H
H
H
C
H
C CH
H
CH3
H
H
-H2O
-KBr
C
H
C CH
H
CH3
H
H
1-butene (20%)
Br
-H2O
Br
1° carbocation(less stable)
2° carbocation (stable)
-KBr
C
H
C C
H
CH3
H
H
H
2-Butene (80 %)
29Mr. Mote G.D

30. 2. Dehydrohalogenation of alkyl halides
(β-Elimination reaction)
• E1 Mechanism: in this mechanism, breaking of the C-X bond is
complete before any reaction occurs with base to lose
hydrogen and before the carbon-carbon double bond is
formed.
• This mechanism is designated E1, E- elimination 1-
unimolecular
• E.g. reaction of 2-bromo -2- methyl propane to form 2-methyl
propene which follows two step mechanism via carbocation
intermediate.
CH3 C
CH3
Br
CH3
2-Bromo 2-methyl propane
CH3OH
methanol
CH3 C
CH3
CH2
2-methyl propene
CH3 O
H
H
30Mr. Mote G.D

31. CH3 C
CH3
Br
CH3
2-Bromo 2-methyl propane
CH3 C
CH3
CH3
carbocation
slow, rate
determining
Br
CH3 O
H
H2C C
CH3
CH3
H
H2C C
CH3
CH3
3HC
O
H
H
Step-I
Step-II
fast
2-methyl butene
E 1 Mechanism
31Mr. Mote G.D

32. 2. Dehydrohalogenation of alkyl halides
(β-Elimination reaction)
• E2 Mechanism: this a concerted process, E stands for
elimination 2- stands for bimolecular because the base
removes a β- hydrogen at the same time the C-X bond is
broken to form alkyl ion.
• The rate law for the rate determining step is
dependent on both the alkyl halide and base.
• Rate: k[alkyl halide][base], if base is strong then E2
mechanism is operated.
CH3 CH2 CH2 Br
n-
bromo propane
CH3 CH2OH
NaOH
CH3 C
H
CH2 NaBr
CH3 CH2OH
ethanol
propene
H2O
32Mr. Mote G.D

33. E 2 Mechanism
H3C
H
C CH2 Br
CH3 CH2 OH
NaOH
CH3 CH2 O-
ethoxide ion
H
CH3 CH2 ONa
ethoxide ion
Na+
CH3 CH2 O-
ethoxide ion
Na+
CH3 CH2OH
ethanol
CH3 C
H
CH2
propene
NaBr
1. In this mechanism, proton transfer to the base, formation of carbon-carbon double bond
Ejection of bromide ion occurs simultaneously, that is all bond forming and breaking occur at
the same time.
2. Product is formed according to saytzeff rule.
33Mr. Mote G.D

34. Carbocation rearrangement
34Mr. Mote G.D
CH3 C
H
C C
CH3
Cl
H2SO4
-HCl
CH3
H
C C C
CH3
CH3
CH3
CH3
H
CH3
Mechnism:
CH3 C
H
H
C C
CH3
Cl CH3
CH3
H
H-OSO3H
-HCl
CH3
H
C C C
CH3
CH3
CH3
H
2° Carbocation
CH3
H
C C C
CH3
CH3
H
CH3
CH3
H
C C C
CH3
CH3CH3
OSO3H
-H2SO4
CH3
CH3
CH3
3° Carbocation
CH3CH3
2-chloro-3,3,4-trimethylpentane 2,3,4-trimethylpent-2-ene
less stable
highly stable

35. E1 Versus E2
Sr.
no
E1 E2
1 Unimolecular reaction Bimolecular reaction
2 Two step reaction One step reaction
3 Carbocation intermediate formed No Carbocation intermediate formed
4 No transition state is formed transition state is formed
5 Polar protic solvent is good Polar aprotic solvent is best
6 Strong nucleophile not interferes
reaction
Strong nucleophile fasters the reaction
7 Slow rate determining step Fast rate determining step
8 Rearrangement may takes place There is no rearrangement
9 Bond formation and bond breaking
is not simultaneous
Bond formation and bond breaking is
simultaneous
10 Reaction rate is increases when
substrate concentration increases
Reaction rate is increases when substrate
and base concentration increases
11 No stereo specific Antiperiplanar (stereo specific)
12 Follows saytzeff rule Follows saytzeff rule
13 Β-elimination Β-elimination 35Mr. Mote G.D

36. Factor affecting on E1 and E2
Sr.
no
E1 E2
1 Good leaving group- alcohol Better leaving groups faster the reaction
2 Reactivity order: 3°>2°>1° Reactivity order: 3°>2°>1°
3 Stable carbocation-tertiary
carbocation
4 Weak bases-Water or Alcohol Favored by strong base
5 Polar protic solvents Polar aprotic solvents
6 Only substrate concentration
fasters the reaction
substrate concentration as well as strong
base fasters the reaction
7 First order kinetics Second order kinetics
8
9
10
11
12
36Mr. Mote G.D

37. 3. Dehalogenation of vicinal dihalide
• Dehalogenazion involves the removal of a molecule ( X—
X)from a reactant molecule.
• A compound having two halogen atoms on adjacent carbon
atoms called a vicinal dihalide (or vic .dihalide).
• The treatment of vic-dihalides with zinc dust using ethyl
alcohol as solvent, results in dehalogenation, and an alkene is
formed.
R C
H
CH
H
BrBr
vic-dihalide
Zn
ethanol R C
H
CH
H
alkene
ZnBr2
H3C C
H
CH
H
BrBr
1, 2 dibromo propane
Zn
ethanol H3C C
H
CH
H
propene
ZnBr2
37Mr. Mote G.D

38. 4. Controlled hydrogenation of alkyne
1. Alkynes undergoes hydrogenation in the nickel or palladium
or platinum to form alkenes
R C C H
alkyne
H2
Ni
250-300
°C
R C
H
CH2
H3C C C H
methyl acetylene
H2
Ni
250-300
°C
H3C C
H
CH2
ethene
38Mr. Mote G.D

39. 5. Pyrolysis (Cracking)
• The decomposition of a compound by heat is called pyrolysis.
• This process when applied to alkane is known as cracking.
• Larger alkanes are broken into a mixture lower molecular
weight alkanes, alkenes and hydrogen
CH3 CH3
500°C
absence
of air
CH2=CH2
CH4 H2
Ethane Ethene
2 2 2
Methane
39Mr. Mote G.D

40. reactions of alkenes
1. Addition of hydrogen halides.
2. Addition hypohalous acids.
3. Addition of sulphuric acid.
4. Addition of water.
5. Addition halogens.
6. Addition of hydrogen
7. Catalytic oxidation
8. Oxidation with potassium permanganate
9. Ozonolysis
10. Polymerization.
11. Oxymercuration-demercuration of alkenes
40Mr. Mote G.D

41. Electrophilic addition reactions
1. Alkenes contain carbon- carbon double bond to which treatment
of hydrogen halide.
2. Initially addition of hydrogen(electrophile) to form carbocation
3. carbocation attacked by halide( nucleophile) to form addition
product, that addition reaction is called as electrophilic addition
reaction
41Mr. Mote G.D
C
H
CH2 H+
H
C CH2
R
HBr H+
Br-
R
H
H
C CH2R
H
Br
alkyl halide
H2C CH2 HBr CH3 CH2 Br
ethyl bromide
ethylene
C
H
C
H HBr
2-Bromo butane2-Butene
H3C CH3
C
H
C
H
H3C CH3
BrH
Br-
Mechanism
examples

42. 1. Addition of hydrogen halides
1. Alkenes react with hydrogen halides (HCl, HBr or HI) to form
alkyl halides.
H2C CH2 HBr CH3 CH2 Br
ethyl bromide
ethylene
C
H
C
H HBr
2-Bromo butane2-Butene
H3C CH3
C
H
C
H
H3C CH3
BrH
42Mr. Mote G.D

43. Markovnikov rule
1. If alkene is unsymmetrical, the H+of HX goes to the double
bonded carbon that has already greatest number of
hydrogen's.
e.g. reaction of HCl with propene yields 2-chloropropane.
CH3 C
H
CH2
propene
HCl
CH3 C
H
Cl
CH3
2-Chloro propane
43Mr. Mote G.D

44. Markovnikov rule
1. formation of carbocation, two types of carbocations are
possible.
2. Bromide ion attacks the more stable secondary carbocation
3. The order of stability of carbocation 3°> 2°>1°
CH3 C
H
CH2
propene
HCl
CH3
H
C CH3
2° Carbocation
(more stable)
HCl
CH3 CH2 CH2
1° carbocation
(less stable)
Br CH3 CH
Br
CH3
2-Bromo propane
(markovnikov product)
44Mr. Mote G.D

45. Markovnikov rule
4. Secondary carbon has lower energy, more stable secondary
carbocation hence lower energy transition state and faster
rate of formation.
45Mr. Mote G.D

46. Anti-markovnikov rule
• the H+of HX goes to the double bonded carbon that has
already least number of hydrogen's. in presence of peroxide is
known as anti- markovnikov.
• E.g. propylene reacts with HBr in the presence of a by a free
radical mechanism.
46Mr. Mote G.D
Sr.no Markovnikov Antimarkovnikov
1 H of goes to double bonded carbon
atom which has greatest number of
hydrogen atom
H of goes to double bonded carbon atom
which has least number of hydrogen atom
2. Initially hydrogen goes to carbon to
carbocation
Initially halogen goes to carbon atom
which has greatest number of hydrogen
atom
3. Secondary carbocation
intermediate formed
Secondary free radical intermediate
formed
4. Peroxide effect is not considered Peroxide effect is considered
5. Electrophilic addition reaction Free radical addition reaction

47. Mechanism of antimarkovnikov rule
(free radical addition reaction)
1. Peroxide dissociates to give alkoxy free radicals.
2. Alkoxy free radical attacks HBr to form a bromine atom( free radical)
3. Bromine atom can attack propylene to give a primary free radical and a
secondary free radical.
4. More stable secondary free radical attacks H+ form n- propyl bromide
R O O R 2R O
2R O HBr R OH Br
Br CH2 C
H
CH2
CH3
H
C CH2
Br
CH3
H
C CH2
Br
H CH3 CH2 CH2Br
n- propyl bromide 47Mr. Mote G.D

48. 2. Addition of hypohalous acids
1. Alkenes react with hypohalous acid to give halohydrins.
H2C CH2
HOCl 2HC CH2
HO Cl
ethylene chlorohydrin
48Mr. Mote G.D
CH3 C
H
CH2
HO Cl H3C
H
C CH2
OH Cl
HO Cl + OH
CH3 C
H
CH2 H++ CH3
H
C CH2
Cl
OH
H3C
H
C CH2
OH Cl
prop-1-ene
2- chloro propanol
Cl

49. 3. Addition of sulphuric acid
1. Sulphuric acid undergoes addition reaction to an alkene to
form alkyl hydrogen sulfate.
49Mr. Mote G.D
CH3 C
H
CH2
H OSO3H H3C
H
C CH2
OSO3H H
H OSO3H H+ + OSO3H
CH3 C
H
CH2 H++ CH3
H
C CH2
H
OSO3H
H3C
H
C CH2
OSO3H H
prop-1-ene
isopropyl hydrogen sulfate

50. 4. Addition of water
1. Water adds to alkene in presence of acid catalyst form
alcohol
50Mr. Mote G.D
H OH- H+ + OH-
CH3 C
H
CH2 H++ CH3
H
C CH2
H
OH-
H3C
H
C CH2
OH H
prop-1-ene
2-Propanol
C
H
CH2
propene
C
H
OH
CH2
H
2- propanol
H2O
H+
H3C H3C

51. 5. Halogenations of alkenes
1. When alkene is treated with halogen in presence of sodium
chloride to give di-halogenated alkane.
e.g. when ethene is react with chlorine in presence of sodium
chloride to form 1,2 dichloro ethane.
H2C CH2 Cl2
H2C CH2
Cl Cl
NaCl
ethene
1,2-dichloroethane
51Mr. Mote G.D

52. 6. Addition of hydrogen
1. Alkanes can be prepared by the catalytic hydrogenation of
unsaturated hydrocarbons in the presence of catalyst ‘Ni’ or
‘pt’ at 200⁰C to 300⁰C.
R C
H
CH2 H2
Ni

R
H2
C CH3
Alkene
Alkane
H3C C
H
CH2 H2
Ni

H3C
H2
C CH3
propene
Propane
52Mr. Mote G.D

53. 7. Catalytic oxidation
• Alkenes add on oxygen atom across the carbon-carbon double
bond when reacted with oxygen (0 2) in the presence of silver
catalyst, to form expoxides.
• e. g. ethylene undergoes oxidation in presence of silver
catalyst to form ethylene oxides.
H2C CH2 1/2 O2
Ag
H2C CH2
O
oxirane
(ethylene oxide)
ethylene
53Mr. Mote G.D

54. 9. Oxidation with KMnO4
1. Treatment of alkenes with cold, dilute basic KMnO4 leads to 1,2-
diols (vicinal diols).
.e.g. ethylene reacts with cold, dilute basic KMnO4 to form ethane 1,2
diol
H2C CH2
NaOH
H2C CH2
ethylene
KMnO4
OH OH
ethane-1,2-diol
54Mr. Mote G.D

55. 9. ozonolysis
• When ozone is passed through a solution of an alkene in an
inert solvent (CHCI3, or CCl 4) at low temperatures it reacts by
addition across the carbon-carbon double bond of the alkene.
First an unstable intermediate molozonide is formed which
spontaneously isomerises to give the ozonide.
• Ozonide decomposes in presence of zinc to form carbonyl
compounds
55Mr. Mote G.D
H2C CH2
CHCl3
H2C CH2
ethylene
O
O O
O
O O
ozone
1,2,3-trioxolane
HC CH
O O
O
ozonide
Zn/ H2O
H CH
O
H CH
O
ZnO
formaldehyde
CH2
O
O-
CH2
O
3O2 2O3v

56. 10. Polymerization
• Two or more alkene joins together to form new compound
which has several identical units, that reaction is called as
polymerization.
• Addition of alkene together without any loss of atoms that
polymerization is called addition polymerization.
H2C CH2
ethylene
n
H2
C CH2 CH2 CH2
polyethylene
200° c
1500-2000
atm
56Mr. Mote G.D

57. 11. Oxymercuration-demercuration of alkenes
• Mercuric acetate and water add to alkenes called as
oxymercuration
• Reduction of oxymercuration product in presence of sodium
borohydride to form alcohol called as demercuration
57Mr. Mote G.D
CH3 C
H
CH2
CH3 C
H
CH2
Hg
NaBH4
H3C
H
C CH2
OH H
prop-1-ene
2-Propanol
Hg(OOCCH3)2
OH
O C
O
CH3
H2O

58. 11. Oxymercuration-demercuration of alkenes
58Mr. Mote G.D
CH3 C
H
CH2
CH3
H
C CH2
Hg
NaBH4
H3C C
H
CH2
HgOAc
prop-1-ene
OAc
Hg
AcO OAc
OH
HOAc-
-CH3COOH
OH
H3C C
H
CH2
H
OH
Mechanism

59. diene
• An unsaturated hydrocarbon containing two double bond between
carbon atom are called as diene.
• Isolated diene: double bonds are separated by more than one single
bond.
• Conjugated diene: double bonds are separated by one single bond.
• Cumulated diene: double bonds are adjacent
CH3 C
H
C C
H
CH3
cumulated diene
CH3 C
H
C
H
C
H
C
H
CH3
conjugated diene
H2C C
H
H2
C C
H
CH2
isolated diene
59Mr. Mote G.D

60. Preparation of conjugated diene
60Mr. Mote G.D
H2C C
H
C
H
CH2
H2C C
H
H2
C
H2
C
Br2
H2C C
H
H
C CH2
H
-HBr
Br H
KOH-KBr, H2O
1-butene
H2C C
H
C
H
CH2
OH OHH H
-2H2O1,4 butanediol
Cr2O3/Al2O3
H2C C
H
C
H
CH2
H HH H
butane
HC CH
acetylene
CuClNH4Cl
HC C C
H
CH2
vinylacetylene
H2
Lindlar catalyst
1,3butadiene

61. Diels- Alder reaction
• It include the reaction between 1,3 butadiene and ethene to
form cyclohexene(adduct).
1,3 butadiene
ethene
Cyclohexene
61Mr. Mote G.D

62. Electrophilic addition of conjugated diene
• Dienes are treated with hydrogen halides to undergoes 1,2
and 1,4 addition.
H2C C
H
C
H
CH2 HBr H3C
H
C C
H
CH2
H3C C
H
C
H
CH2
HBr
Less stable
more stable
1,4 addition
1,2 addition
H3C
H
C C
H
CH2
Br
2-Bromo-
1 butene
(less stable product2)
62Mr. Mote G.D

63. 1. Addition of hydrogen halides
• Dienes are treated with hydrogen halides to undergoes 1,2
and 1,4 addition.
H2C C
H
C
H
CH2 HBr H3C
H
C C
H
CH2
H3C C
H
C
H
CH2
HBr
Less stable
more stable
1,4 addition
1,2 addition
H3C C
H
C
H
C
H2
Br
1-bromobut-2
-ene
(more stable product 80%)
H3C
H
C C
H
CH2
Br
2-Bromo-
1 butene
(less stable product2)
63Mr. Mote G.D

64. 2. Addition of halogens
• Dienes are treated with halogen to undergoes 1,2 and 1,4
addition.
64Mr. Mote G.D
H2C C
H
C
H
CH2 H2C
H
C C
H
CH2
H2C C
H
C
H
CH2
Br-Br
Less stable
more stable
1,4 addition
1,2 addition
H2C C
H
C
H
C
H2
Br
1,4 dibromo 2-butene
H2C
H
C C
H
CH2
Br
3,4-diromo-
1 butene
(less stable product2)
Br-Br
Br
Br
Br
Br

65. 3. Addition of water
• 1,3 butadiene reacts with water in the presence of H2SO4 to
give a mixture of 1,2 and 1,4 addition products.
65Mr. Mote G.D
H2C C
H
C
H
CH2 H2C
H
C C
H
CH2
H2C C
H
C
H
CH2
H-OH
Less stable
more stable
1,4 addition
1,2 addition
H2C C
H
C
H
C
H2
OH
H2C
H
C C
H
CH2
OH
H-OH
H
H
H
H
but-2-en-1-ol
but-1-en-3-ol

66. 4. Addition of hydrogen
• Dienes are treated with hydrogen hydrogen to undergoes 1,2
and 1,4 addition.
66Mr. Mote G.D
H2C C
H
C
H
CH2 H2C
H
C C
H
CH2
H2C C
H
C
H
CH2
H-H
Less stable
more stable
1,4 addition
1,2 addition
H2C C
H
C
H
C
H2
H
H2C
H
C C
H
CH2
H
H-H
H
H
H
H
but-2-ene
but-1-ene

67. 5. Polymerization
• 1,3 butadiene polymerizes in the presence of peroxide to give
polybutadiene
67Mr. Mote G.D
H2C C
H
C
H
CH2
H2
C
H2
C C
H
C
H
H2
C
peroxide
 n

68. Free radical addition of conjugated diene
• Dienes also undergoes free radical chain reaction to form 1,4
addition product.
H2C C
H
C
H
CH2
H2C
H
C C
H
CH2
H2C C
H
C
H
CH2
HBr
more stable
1,4 addition
1,2 addition
H2C
H
C C
H
CH2
H
4-Bromo -1 butene
(less stable product)
HBr H Br
Br
Br
Br
H2C C
H
C
H
CH3
Br
1 Bromo 2-butene
(more favoured product)
Br
68Mr. Mote G.D

69. Allylic rearrangement
• Allylic compounds are those which have a functional group on
a carbon atom α to an olefinic bond.
• Allylic compounds undergo acid or base catalyzed migration to
form new compound.
R C
H
C
H
C
H
H
OH
H+
R C
H
C
H
CH
H
OH
H3C C
H
C
H
C
H
H
OH
H+
H3C C
H
C
H
CH
H
OH
but-2-en-1-ol
but-3-en-2-ol
Mechanism
H3C C
H
C
H
CH
H
H3C C
H
C
H
CH
H
H3C C
H
C
H
C
H
H
OH
but-2-en-1-ol
H+
OH-
H3C C
H
C
H
CH
H
OH
but-3-en-2-ol
69Mr. Mote G.D

70. Stability of alkenes
• tetra substituted alkenes are more stable than tri, di mono substituted alkenes.
• In di-substituted alkenes , Trans form is more stable than cis form of di-substituted alkenes.
• Because more substitution leads to more conjugation, more conjugation directly proportional
to stability.( Hyper conjugation means number of alpha hydrogen to alpha carbon atoms)
• Less stable isomer has higher energy which is identified by heat of hydrogenation.
• E.g. Cis 2-butene exerts -28.6 kcal/mole energy while trans 2-butene exerts -27.6 kcal/mole
energy on hydrogenation of 2-butene.
70Mr. Mote G.D
C C
H
CH3
H
H3C
C C
H
CH3
H3C
H
Cis- 2-Butene Trans- 2- Butene
CH
H3C
CH
CH3
H H
butane
H=-28.6
CH
H
CH
CH3
H3C H
butane
H=-27.6
H2
H2

71. Stability of conjugated diene
• Conjugated dienes are more stable than isolated dienes, because conjugated diene shows
resonance stabilization effect but isolated dienes does not shows resonance stabilization.
71Mr. Mote G.D
C C
H
CH2
H
H2C
C CH
H
C
H
H2C
H
1,3 butadiene
CH
H3C
C
CH2
H H
1-butane
H=-57.6
CH
H
CH
C
H
H3C H
1-pentene
H=-60.8
H2
H2
CH2
penta-1,4-diene
CH2

72. Stability of alkenes
72Mr. Mote G.D

73. Thank you
73Mr. Mote G.D