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Class notes chemistry Chemistry Simplified NCERT Class 11
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Class notes chemistry Chemistry Simplified NCERT Class 11
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UNIT 13 HYDROCARBONS Organic compounds containing carbon and hydrogen atoms only are called
hydrocarbons.
Depending on the types of CC bond, hydrocarbons are classified into three.
Saturated Hydrocarbons, Unsaturated Hydrocarbons and Aromatic hydrocarbons.
If carbon atoms form closed chain or a ring, they are called cycloalkanes.
Saturated Hydrocarbons contain CC and CH single bonds.
Unsaturated Hydrocarbons contain CC multiple bonds.
i.e., double bonds, triple bonds or both.
Aromatic hydrocarbons are a special type of cyclic compounds.
They are also called arenes.
ALKANES
Alkanes are saturated open chain hydrocarbons containing CC single bonds.
The general formula for alkanes is CnH2n+2
Where ‘n’ stands for number of carbon atoms and 2n+2 stands for number of hydrogen
atoms in the molecule.
NOMENCLATURE
1)
Hex-2-ene
2)
2-Methyhex-3-ene
3)
1,3-pentadiene
4)
1,4-pentadiene
5)
2-methyl-1,3-butadiene
____________________________________________________________________________________________
Prepared by HAIZEL G. ROY, HSST (HG) Chemistry, Govt. H.S.S. Kalamassery, Ernakulam Page | 1
,6. Write the structures of different chain isomers of alkanes corresponding to the
molecular formula C6H14. Also write their IUPAC names.
7. Write the IUPAC names of the following compounds
a) (CH ) CCH C(CH )
33 2 33
2,2,4,4-Tetramethylpentane
b) (CH )2C(C2H5 )2
3
3,3-DimethylpPentane
8. Write the structural formulas of the following compounds.
(i) 3,4,4,5-Tetramethylheptane
(ii) 2,5-Dimethylhexane
9. Write the structures for each of the following compounds. Why are the given names
incorrect? Write their correct IUPAC Names.
(i) 2-Ethyl Pentane
____________________________________________________________________________________________
Prepared by HAIZEL G. ROY, HSST (HG) Chemistry, Govt. H.S.S. Kalamassery, Ernakulam Page | 2
, Longest chain is of six carbon atoms and not that of five.
Hence the correct name os 3-Methylhexane
(ii) 5-Ethyl-3-Methyl Heptane
Numbering is to be started from the end which gives lower number to ethyl group.
Hence, correct name is 3-ethyl-5-methylheptane
PREPARATION OF ALKANES
1. FROM UNSATURATED HYDROCARBONS
Dihydrogen gas adds to alkenes in the presence of finely divided catalysts like Nickel,
Platinum or Palladium to form alkanes.
This process is called Hydrogenation.
2. FROM ALKYL HALIDES
Alkyl halides except fluorides on reduction with Zn and dil. HCl gives alkanes.
CH3Cl + H2 Zn CH
dil. HCl 4 + HCl
Alkyl halides on treatment with sodium metal in dry ether gives higher alkanes.
This reaction is known as Wurtz Reaction.
Zn
CH3Br + 2Na + CH3Br CH3 -CH3 + 2NaBr
dil. HCl
3. FROM CARBOXYLIC ACIDS
A. DECARBOXYLATION
Sodium salts of carboxylic acids on heating with soda lime gives alkanes containing
one carbon atom less than the carboxylic acid.
The process of elimination of CO2 from a carboxylic acid is known as
Decarboxylation.
NOTE
Sodalime is a mixture of Sodium Hydroxide (NaOH) and Calcium Oxide (CaO).
____________________________________________________________________________________________
Prepared by HAIZEL G. ROY, HSST (HG) Chemistry, Govt. H.S.S. Kalamassery, Ernakulam Page | 3
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