Hydrocarbon

Organic Chemistry : National Examination Board, Nepal
Alkane
Alkene
Alkyne
Dr. Damodar Koirala
Amarsingh Model Secondary
School
Pokhara, Nepal

Dr. Damodar Koirala koirala2059@gmail.com
Hydrocarbons
• Organic compounds containing carbons and hydrogens
only. Eg: Alkane, alkene, alkyne, benzene
• Saturated hydrocarbon: Organic compound with
general formula CnH2n+2. There is no multiple bond or a
ring in saturated hydrocarbon. Acyclic alkane is only
example of saturated hydrocarbon
• Unsaturated hydrocarbon: Hydrocarbon with general
formula other that . There is a multiple bond or a ring.
Eg: alkene, alkyne, cyclic hydrocarbon…
2

Alkane and nomenclature
• General formula : CnH2n+2, where n = 1,2,3,4….
3
1. Find the longest chain called parent chain
2. The substituent carbon has lowest possible number
3. The sum of numbers used to indicate the positions of
various alkyl groups must be the lowest
4. When same substituent is present more than once on the
chain then di, tri, tetra etc are used together with a set of
locants

Isomerism in Alkane
• Only chain isomerism is possible for alkane
• Only for alkane with carbon number greater than 3
• Write the isomers of C5H10.
4

Structure of Alkane
• All Carbon of alkane has sp3 hybridization
• The bond angle is 109.5
5
Ethane

Preparation of alkane
• Hydrogenation of Alkene and Alkyne
• Decarboxylation of Carboxylic acids
• Reduction of Alkyl Halide
• Action of Sodium on Alkyl Halides (Wultz Reaction)
6

Catalytic Hydrogenation of Alkene and Alkyne:
• Hydrogenation of alkenes or alkyne in presence of
nickel or platinum catalyst produces alkane
7
** Methane can not be produced by this method
*Make sure to name all organic compounds involved in chemical reaction
CH2=CH2 + H2 CH3CH3
Ni or Pt
300 C
HCCH + 2H2 CH3CH3
Ni or Pt
300 C

Decarboxylation of Carboxylic acids
• When sodium salt of carboxylic acid is heated with
soda lime ( NaOH and CaO in 3:1 ratio), a molecule
of CO2 is eliminated to produce alkane.
8
** The carbon chain length is reduced by 1
RCOONa + NaOH RH + Na2CO3
CaO
Heat
RCOOH RH + Na2CO3
Soda lime
Heat
CH3COONa + NaOH CH3CH3 + Na2CO3
CaO
Heat

Reduction of Alkyl Halide
• In presence of zinc and HCl, alkyl halide is reduced
to alkane
9
R-Cl + Zn + 2HCl R-H + ZnCl2 + HCl
CH3CH2Cl + Zn + 2HCl CH3CH3 + ZnCl
2
+ HCl
*Make sure to name all organic compounds involved in chemical reaction

Action of Sodium on Alkyl Halides (Wultz Reaction)
• Two molecules of alkyl halide when heated with Na
metal in presence of dry ether, they lose their halogen
atoms and the joining of two alkyl group produces a
symmetric alkane (R-R) with even number of carbon.
10
CH3-Br + Na + Br-CH3 CH3-CH3 + 2NaBr
Dry ether
R-Br + Na + Br-R R-R + 2NaBr
Dry ether
CH3CH2-Br + Na + Br-CH2CH3 CH3CH2-CH2CH3 + 2NaBr
Dry ether

Alkane: Chemical reaction
• The alkanes the least chemically reactive class of
organic compounds because alkanes do not contain
any function group and contain strong carbon-
carbon single bonds and strong carbon-hydrogen
bonds.
11

Alkane: Chemical reaction
• Substitution reaction
• Halogenation
• Nitration: Substitution of -NO2 group for H)
• Sulphonation (Substitution of -SO3H for H)
• Oxidation of ethane
12

Halogenation
13
• Alkane reacts with halogen in presence of sunlight to produce
haloalkane
• Here, -H of alkane is substituted with -X
• Substitution continues until all “H” is replaced by “X”
CH4 + Cl2 CH3-Cl + HCl
CH3-Cl + Cl2 CH2Cl2 + HCl
CH2Cl2 + Cl2 CHCl3 + HCl
CHCl3 + Cl2 CCl4 + HCl
Sunlight
Sunlight
Sunlight
Sunlight

Nitration
14
• Alkane reacts with nitric acid to produce nitroalkane
• Here, -H of alkane is substituted with -NO2
Alkane + Nitric acid Nitroalkane
CH3-CH3 + HNO3 CH3-CH2NO2 + H2O
CH4 + HNO3 CH3NO2 + H2O

Alkane + Sulphuric acid alkane sulphonic acid
Sulphonation
15
• Alkane reacts with sulphonic acid to produce alkane
sulphonic acid
• Here, -H of alkane is substituted with -SO3H
CH3-CH3 + H2SO4 CH3-CH2SO3H + H2O

Combustion of alkane
• Reaction of alkane with air produces CO2 and H2O
16
CH4 + 2O2 CO2 + 2H2O
C2H6 + 7/2 O2 2CO2 + 3H2O
C3H8 + 5 O2 3CO2 + 4H2O

Oxidation of ethane
• Ethane reacts with O2 in presence of MnO catalyst
to produce ethanal
17
CH3-CH3 + O2 CH3-CHO + H2O
MnO

Alkene and nomenclature
18
• Organic compound with at-least one double in it
• The general formula of alkene is CnH2n
• For naming: Determine the longest carbon chain containing
double bond in it then provide lowest number to the double bond.
• Name as alk-position-ene (position is required only if more that 3
carbon is involved in parent chain)

Isomerism in alkene
19
• Chain isomerism
• Positional isomerism
• Geometric isomerism (cis-trans or e-z)
• Ring-Chain isomerism

Chain Isomerism in alkene
20
• Two alkenes with same molecular formula and
different parent chain (or different chain length)
CH2=CH-CH2-CH3
CH2=C-CH3
CH3

Positional Isomerism in alkene
21
• Two alkenes with same molecular formula, same
parent chain but double bond in different position.
CH2=CH-CH2-CH3
CH3-CH=CH-CH3

Cis-trans Isomerism in alkene
22
• For disubstituted alkene
• Alkene except Ethene and propene shows cis-trans
isomerism

Symmetric and asymmetric alkene
23
• Alkene with same groups on two side of double bond is
symmetric alkene.
• Alkene with different groups on two sides of double bond is
asymmetric alkene
CH3CH=CHCH3 CH2=CHCH2CH3
CH3CH2CH=CHCH2CH3 CH3CH=CHCH2CH2CH3

Structure of alkene
24
• The carbon involved in double bond have sp2
hybridization
• The bond angle is 120
pi bond in ethene
Sigma bonds in ethene

Structure of ethene
25
Orbitals structure in ethene

Preparation of alkene
26
• Dehydrohalogenation of haloalkane
• Dehydration of alcohol
• Catalytic hydrogenation of alkyne

Dehydrohalogenation of haloalkane
27
• Haloalkane reacts with alcoholic KOH or
alcoholic NaOH loses HX to produce alkene

Dehydrohalogenation of haloalkane
28
• If two alkene are possible then the one with most substituted
alkene is preferred (Saytzeff’s rule)
• Saytzeff’s rule: “when an alkyl halide reacts with alcoholic
solution of potassium hydroxide and if two alkenes are
possible, then the one which is more substituted, will be the
major product”

Dehydration of alcohol
29
• In presence of dehydrating agent, alcohol losses
water to produce alkene
• In presence of dehydrating agent, alcohol losses
water to produce alkene

Catalytic hydrogenation of alkyne
30
• Alkyne reduces to alkene in presence of Pd on Barium
sulphate and quinoline. The catalyst is called Lindar’s catalyst
BaSO4
• It is called partial reduction since the reduction of alkene
does not proceed further to alkane.

Alkene: Chemical reaction
• Addition
• Hydrogen
• Hydrogen halide (Markovnikov’s and Anti
Markovnikov’s)
• Water
• Ozone
• Oxidation with alkaline KMnO4 (Bayers reagent)
31

Hydrogenation
• Addition of hydrogen to unsaturated hydrocarbons
takes place in the presence of a catalyst like Ni, Pt or
Pd.
32

Halogenation
• The reddish-brown color of Br2 gets 2 discharged. This
reaction is also used as test for unsaturation in hydrocarbons.
33
• Alkene adds to halogen to produce dihaloalkane

Hydrohalogenation
• When halogen acids are alkene, halogen adds to one
carbon and hydrogen adds to another carbon of the
double bond.
34

Hydrohalogenation
• In case of unsymmetrical alkenes (which contain unequal number of H-atoms
attached to the carbon atoms of the double bonds), the addition of HX takes
place according to the Markownikoff’s rule.
• This rule states that in the addition of halogen acids to unsymmetrical alkenes,
the halogen of HX goes to that carbon atom of C = C bond which already has
less H-atoms attached to it.
• In other words, hydrogen atom of HX goes to the carbon atom with more
number of H-atoms attached to it.
35

Hydrohalogenation
• If the addition of HBr is carried out in the presence of peroxides such as
benzoyl peroxide, then the reaction takes place contrary to Markownikoff’s rule.
This is also known as Anti Markownikoff’s addition or peroxide effect.
36

Hydration
• Alkene is hydrate to alcohol in presence of dilute acid
37

Ozonolysis
• Ozone adds to the alkene forming ozonide. The ozonide
when further reacted with water in the presence of zinc dust,
forms aldehydes or ketones, or both.
• This process of addition of ozone to an unsaturated
hydrocarbon followed by hydrolysis is called ozonolysis.
38

Oxidation with Bayers reagent
• When an alkaline solution of KMnO4
(Baeyer’s
Reagent) is added to an alkene, the purple colour of
KMnO4 gets discharged. This reaction is used to test
unsaturation in hydrocarbons.
39

Alkyne and nomenclature
40
• Organic compound with atleast one triple bond in it
• The general formula of alkene is CnH2n-2
• For naming: Determine the longest carbon chain containing
triple bond in it then provide lowest number to the triple bond.
• Name as alk-position-yne

Isomerism in alkyne
41
• Chain isomerism
• Positional isomerism
• Functional isomerism

Chain Isomerism in alkyne
42
• Two alkynes with same molecular formula and
different parent chain (or different chain length)
CH3CH2CH2C≡CH
CH3-CH-C≡CH
CH3

Positional Isomerism in alkyne
43
• Two alkynes with same molecular formula, same
parent chain but triple bond in different position.
CH3-CH2-CH2-C≡CH
CH3-CH2-C≡C-CH3

Functional Isomerism in alkyne
44
• Functional isomers of alkyne are diene.
• Dienes are organic compounds with two carbon-
carbon double bond on them
CH3C≡CCH3
CH2=CHCH=CH2

Structure of alkyne
45
• The carbon involved in double bond have sp hybridization
• The bond angle is 180
Orbitals structure in ethyne: there are two pi bonds

Preparation of alkyne
46
• Carbon and hydrogen
• Dehydrogenation of vicinal dihalides (1,2-
dibromoethane)
• Reaction of iodoform with silver powder

Dehydrogenation of vicinal dihalides
47
• Vicinal dihalides when treated with alcoholic KOH produces
alkyne. It occurs in two steps.
• Vicinal dihalides when treated with NaNH2 produces alkyne. It
occurs in one step.
NaNH2

Reaction of iodoform with silver powder
48
• When iodoform is heated with silver powder,
ethyne is obtained

Alkyne: Chemical reaction
• Addition
• Hydrogen
• Hydrogen halide
• Water
• Oxidation with alkaline KMnO4 (Bayers reagent)
• Acidic nature
• Action with Sodium
• Ammoniacal AgNO3
• Ammoniacal Cu2Cl2
49

Hydrogenation
• In the presence of a catalyst like Ni, Pt or Pd produces alkane
50
• In the presence of Pd/BaSO4/Quinoline produces alkene
Ni or Pt
300 C
BaSO4

Hydrohalogenation
• Vicinal dihalide is produces
51

Hydration
• Ethyne produces ethanal i.e. aldehyde
52

Oxidation with Bayers reagent
• When an alkaline solution of KMnO4
(Baeyer’s
Reagent) is added to an alkyne, the purple colour of
KMnO4 gets discharged. This reaction is used to test
unsaturation in hydrocarbons.
53

Test reaction of alkyne
• With ammonical solution of cuprous chloride produces red ppt
• With ammonical solution of silver nitrate produces white ppt
54

Acidic character of hydrocarbon
• The acidic nature of hydrocarbons can be determined
with the help of the percentage (%) of s-character of the
hydrocarbon. The greater the percentage of s-character
of a hydrocarbon, the more will be its acidic nature.
55

Test of Alkane/Alkene/Alkyne
56

57

Kolbe’s electrolysis
• Kolbe’s electrolysis can be used to prepare alkane, alkene and alkyne
• Electrolysis of the salts of monocarboxylic acids results in formation
of alkane
58
O
O
Electrolysis
Electrolysis

• Electrolysis of the salts of dicarboxylic acids results
in formation of alkene
59

• Electrolysis of the salts of dicarboxylic acids results
in formation of alkene
60

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