|
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.
|
