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Homologous Seriesy A series of organic compounds with similar chemical
properties, in which each member differ by CH2 is
called the homologous series.
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Homologous
series
General
formula
Example Functional
group
Alkanes CnH2n + 2 CH4
Alkyl CnH2n + 1 CH3
Alkenes CnH2n C2H4 C = C
Alkynes CnH2n í 2 C2H2 C C
Alcohols CnH(2n + 1)OH CH4O - OH
Carboxylic acid CnH2n+1COOH CH2O2 - COOHEster RCOOR¶
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Alkanes :
CnH2n+2 , n = 1,2,3,.
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Formula Branch or name of group
CH3 - methyl
C2H5 - ethylC3H7 - propyl
C4H9 - butyl
C5H11 - pentyl
A) IUPAC (International Union of Pure and Applied Chemistry)
± is used to name organic compound.
Organic compound is divided into three portions which is Prefix + Root + Suffix.
1.Prefix ± name of the branch or side chain.
General formula: CnH2n+1 ±Where n = 1, 2, 3, « (n = number of carbon)
Alkyl group signifies that it is not part of the main chain.
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Number of side chain Prefix
2 Di-
3 Tri-
4 Tetra-
5 Penta-
6 Hexa-
Two or more types of branches are present, name them in
alphabetical order.
More than one side chains are present, prefixes are used.
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Number of carbon
atoms
Root name
1 meth-2 eth-3 prop-4 but-
5 pent-6 hex-7 hept-8 oct-9 nan-10 dec-
2.Root ± the parent hydrocarbon (denotes the longest carbon chain).
�The longest continuous (straight chain) carbon chain is selected.
�Identify the number of carbon.
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Homologousseries
Functionalgroup
Suffix
Alkane - C C - -ane
Alkene - C = C - -ene
Alcohol OH -olCarboxylic acid COOH -oic
Ester COO -oate
3. Suffix ± f unctional group.
Prefix + Root + Suffix
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Naming Alkanesy IUPAC rules :
y Choose the longest continuous carbon chain as the
parent chain. Carbon atoms are numbered startingfrom whichever end that gives the lower value forthe 1st substituent.
y Prefix di-, tri-, tetra,is used to indicate the same
substituents in the molecule.
y Substituents are named in the order of increasingsize or in alphabetical order.
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Physical Properties of AlkaneName Molecular
formula
RMM Density
(g cm-3)
Physical state at
25°C
Methane CH4 16 - Gas
Ethane C2H6 30 - Gas
Propane C3H8 44 - Gas
Butane C4H10 58 - Gas
Pentane C5H12 72 0.63 Liquid
Hexane C6H14 86 0.66 Liquid
Heptane C7H16 100 0.68 Liquid
Octane C8H18 114 0.70 Liquid
Nonane C9H20 128 0.72 Liquid
Decane C10H22 142 0.73 Liquid
.
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Name Formula Number of isomers
Methane
EthanePropane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
Undecane
Dodecane
Tridecane
Tetradecane
Pentadecane
Eicosane
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
C11
H24
C12H26
C13H28
C14H30
C15H32
C20H42
2
3
5
9
18
35
75
159
355
802
1858
4347
360000
gas
liquid
solid
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Physical PropertiesName Physical
StateDensity (g cmí3)
Solubility in water
Electrical conductivity
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
OctaneNonane
Decane
0.63
0.66
0.68
0.700.72
0.73
Insoluble in
water
Cannot
conduct
electricity
gas
liquid
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Physical Properties of Alkane.
Solubility in water ± all members in alkanes are insoluble in water but soluble in many organic solvent (benzene and ether ).
Density of alkane ± the density of water is higher than density of
alkane.
When going down the series, relative molecular mass of alkanes is
higher due to the higher force of attraction between molecules and
alkane molecules are packed closer together.
Electrical conductivity ± all members in alkanes do not conduct
electricity.
Alkanes are covalent compounds and do not contain freely moving ions.
Boiling and melting points ± all alkanes in general have low
boiling points and melting points.
Alkanes are held together by weak intermolecular forces.
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Chemical properties of Alkane
Reactivity of alkanes
Alkanes are less reactive (saturated hydrocarbon).
Alkanes have strong carbon-carbon (C ± C) bondsand carbon-hydrogen (C ± H) bonds.
All are single bonds which require a lot of energy to
break.
Alkanes do not react with chemicals such as oxidizing agents, reducing agents, acids and
alkalis.
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Chemical properties of Alkane
Substitution reaction of alkanes
(Halogenation)
Substitution reaction is one atom (or a group of atoms) in a molecule is replaced by
another atom (or a group of atoms).
Substitution reaction of alkanes take place in
ultraviolet light.
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Example:
Alkanes react with bromine vapour (or chlorine) in
the presence of UV light.
CH4 + Cl2 ±> HCl + CH3Cl (Chloromethane)CH3Cl + Cl2 ±> HCl + CH2Cl2 (Dichloromethane)
CH2Cl2 + Cl2 ±> HCl + CHCl3 (Trichloromethane)
CHCl3 + Cl2 ±> HCl + CCl4 (Tetrachloromethane)
The rate of reaction between bromine and alkanes
is slower than the rate of reaction between chlorine
and alkanes
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Combustion of Alkanesy Combustion of alkanes
Complete combustion of hydrocarbons
C x H y + ( x + y/4) O2 > x CO2 + y/2 H2OCH4 + 2O2 > CO2 + 2H2O
y Incomplete combustion
occurs when insufficient supply of oxygenCH4 + O2 > C + H2O2CH4 + 3O2 > 2CO + 4H2O
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Isomers
Butane, C4H10
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( A)
(B)