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 C_nH_{2n + 2}

 

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

2) Alcohols having the general formula C_nH _{2n + 1}OH

CH3-OH	Methanol
CH3-CH2-OH	Ethanol
CH3(CH2)2OH	n-Propanol
CH3 (CH2)3OH	n- butanol

 

 

 

3) Amines having the general formula C_nH_{2n + 1}NH₂

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.