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13.5 Hydro Carbons

One of the important families of organic compounds is the Hydrocarbon family. Hydrocarbons as the name implies, are compounds whose molecules contain only carbon and hydrogen. They can be divided into several groups, as summarized below, based on the nature of the carbon skeleton and the type of bond that exists between the individual carbon atoms.

Following are some of the examples of hydrocarbons:

Homologous series :

A series of compounds which have a common general formula and in which each member differs from the next member by a constant unit, which is the methylene group (- CH2-) is called the homologous series. Members of a homologous series are called homologs.

A few examples of the homologous series with some of their homologs are given below.

1) Straight chain alkanes having general formula CnH2n + 2

Table 24

Structure

Name

1. CH4

Methane

2. CH3 - CH3

Ethane

3. CH2-CH2-CH3

Propane

4. CH3-CH2CH2CH3

Butane

5. CH3-(CH2)3-CH3

Pentane

6. CH3-(CH2)4-CH3

– Hexane

7. CH3(CH2)5CH3

– Heptane

8. CH3 (CH2)6 CH3

– Octane

9. CH3 (CH2)7CH3

– Nonane

10. CH3 (CH2)8 CH3

n - Decane


Table 25

2) Alcohols having the general formula CnH 2n + 1OH

CH3-OH

Methanol

CH3-CH2-OH

Ethanol

CH3(CH2)2OH

n-Propanol

CH3 (CH2)3OH

n- butanol

Table 26

3) Amines having the general formula CnH2n + 1NH2

CH3-NH2

Methylamine

CH3 CH2 NH2

Ethylamine

CH3(CH2)2 NH2

n-Propylamine

CH3(CH2)3NH2

n-Butylamine

General characteristics of alkanes of a homologous series.

1. Lower members are gases.

2. Members with five to sixteen carbon atoms are liquid.

3. Higher members are solids.

4. Density increases with increase in molecular weight.

5. Boiling point increases with increase in molecular weight.

6. Melting point increases with increase in molecular weight.

7. Insoluble in water but soluble in organic solvents.

8. Exhibit isomerism.

Index

13.1 Introduction
13.2 Functional Groups

13.3 Formula of Organic Compounds
13.4 Geometrical Isomerism
13.5 Hydrocarbons
13.6 Homologous Compounds

Chapter 1





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