Organic Chemistry

1. Alkanes
Organic Chemistry

2. What are Alkanes?
Crude oil is a mixture of compounds called hydrocarbons. Many useful materials can be produced from crude oil. It
can be separated into different fractions using fractional distillation, and some of these can be used as fuels.
Alkanes are chemical compounds that consist of carbon (C) and hydrogen (H) atoms, so they are also called
hydrocarbons. The chemical structure of alkanes only consists of single bonds.
Methane Pentane

3. Homologous series of Alkanes.
Alkane Molecular formula
Methane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
Pentane C5H12
Hexane C6H14
Heptane C7H16
Octane C8H18
Nonane
Decane
C9H20
C9H20
• The alkanes are a family of
hydrocarbons that share the same
general formula. This is: CnH2n+2
• The general formula means that the
number of hydrogen atoms in an
alkane is double the number of carbon
atoms, plus two.
• For example, methane is CH4 and
ethane is C2H6.
• Alkane molecules can be represented
by displayed formulas. In a displayed
formula, each atom is shown as its
symbol (C or H) and each covalent bond
by a straight line.

4. Isomerism In Alkanes
Isomerism
All the alkanes with 4 or more carbon atoms in them show structural isomerism. This
means that there are two or more different structural formulae that you can draw for each
molecular formula.
 For example, an isomer of butane is methyl propane

5. Methane
 Methane is the simplest compound in alkanes series with molecular formula CH4.
 It is the major compound of natural gas which in found in association with petroleum deposits.
 It is found in swamps and marshy places where vegetation decay in the absence of oxygen takes place.
 It also occurs in coal mines, where it is known as fine damp, because it explodes very easily
 STRUCTURE
Composition of methane molecule:
Methane molecule consists of one carbon and four hydrogen atoms (CH4).
Geometry of methane:
Methane molecule is tetrahedral in structure in which carbon is central atom and
four H-atoms are surrounding it in three-dimensions.

6. Tetrahedral Shape
Bond Angles:
HCH-bond angles are 109.5o
.
Bond Length:
All C-H bonds are 1.09Ao
.

7. Laboratory Preparation Of Alkanes
Preparation of methane:
In the laboratory methane is formed by heating sodium ethanoate with a mixture of sodium hydroxide and calcium
oxide, called soda lime.
On heating in the presence of a catalyst, calcium oxide, the -COONa group from sodium ethanoate is replaced by
the hydrogen atom from sodium hydroxide, forming methane and sodium hydroxide gets converted into sodium
carbonate.
Ex: preparation of propane from sodium butanoate.
CH3COONa + NaOH(CaO) → CH4 + Na2CO3

8. PhysicalProperties
Physical Properties of Methane
(i) Methane is a colorless, odorless, and tasteless nonpoisonous gas.
(ii) Methane is sparingly soluble in water but dissolves readily in alcohol and ether.
(iii) Methane is lighter than air.
(iv) Methane melts at -184°C and boils atomic -161.4°C.
(v) Methane like carbon dioxide, also traps infrared radiations (heat radiations) reflected by the
earth. As a result, methane gas also contributes to the greenhouse effect. Actually, a molecule of
methane traps twenty times more heat radiations than a carbon dioxide molecule.

9. Chemical Properties of Methane
1. Stability:
Chemically, methane is very stable and remains unaffected when treated with KMnO4, K2Cr2O7, H2SO4, HNO3, etc. under normal conditions.
2. Combustion:
Methane burns in excess of air or oxygen with a pale-blue nonluminous flame to give carbon dioxide and water. The combustion reaction is highly exothermic. Therefore,
methane is an excellent fuel.
In the presence of insufficient air (or oxygen), methane undergoes incomplete (or partial) combustion producing carbon monoxide (CO) gas. Carbon monoxide gas is highly
poisonous.
3. Substitution reactions:
The reactions in which one or more hydrogen atoms of a molecule are replaced and by some other atoms or groups are called substitution reactions. The substitution reaction
in which one or more hydrogen atoms are replaced by an equal number of halogen atoms is called halogenations. Saturated hydrocarbons (alkanes) give substitution reactions.
Methane reacts with chlorine (or bromine) in the presence of sunlight or a halogen-carrier to give halo alkenes in which one or more H-atoms are replaced by equal number of
halogen atoms.
4. Action with steam:
Methane gives hydrogen when mixed with steam and the mixture is passed over nickel supported on alumina heated to 1000k.
5. Pyrolysis :
When heated to about 1300 k, methane gets decomposed to give carbon black and hydrogen

10. Uses of methane:
Methane is used as domestic fuel.
It is used in rubber industry.
It is used in the preparation of organic compounds like chloroform, methanol, formaldehyde,
methyl chloride, carbon tetrachloride, etc.
Uses

11. Ethane
Ethane is a hydrocarbon gas made from petroleum. It is the second (first is methane) in a
series of simple hydrocarbon petrochemical compounds in a family of related compounds
named ‘Alkanes’, all of which have the feature of containing only single bonds
between carbon atoms.

12. Properties of Ethane
What are the Properties of Ethane?
The chemical formula for ethane gas is C2H6.
Ethane is a hydrocarbon that exists in nature as an odorless and colorless gas at standard temperature and pressure.
It is a stable compound and shows resistance to reactivity.
It has a molar mass of 30.07 grams per mole (g/mol).
The melting point of ethane is -181.76 °C (89.34 °K) and its boiling point stands at -88.6° C (184.5 °K).
Ethane is soluble in polar solvents like water due to its non-polar nature. Basically, the solubility of ethane is quite low for the formation of a homogeneous
solution.
CHEMICAL PROPERTIES
COMBUSTION REACTION
Ethane burns in air or oxygen with a non-luminous flame to produce carbon dioxide and water. It is an exothermic reaction.
2C2H6 + 7O2 4CO2 + 6H2O + HEAT
HALOGENATION Replacement of halogen with H-atom of an organic compound is called Halogenation. It is a substitution reaction.
CHLORINATION:
C2H6 + Cl2 C2H5Cl C2H4Cl2+ Cl-CH2-CH2-Cl

13. Laboratory Preparation of Ethane
It is prepared in the laboratory by the reduction of ethyl iodide with nascent hydrogen produced from zinc-copper couple
and ethyl alcohol
A mixture of ethyl iodide and alcohol is taken in the dropping funnel and slowly dropped in the flask.Nascent hydrogen
thus produced reduced ethyl iodide to ethane . It is collected by downward displacement of water

14. USES OF ETHANE
Ethane is used in the production of ethylene for making plastics, anti-freeze and detergents; it's a
ripening agent for foods, a refrigerant, a substance in producing welding gas and a primary
ingredient in mustard gas. Ethane is a component in the natural gas methane and is removed by
cryogenic liquefaction.