Hydrocarbons: Introduction, Examples, Types

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Hydrocarbons: Introduction, Examples, Types

Those compounds which contain only carbon and hydrogen are called hydrocarbons. Those hydrocarbons in which all the chains present in the atoms are open are called aliphatic hydrocarbons.

There are two types of aliphatic hydrocarbons-
  1. Aliphatic saturated hydrocarbons
  2. Aliphatic unsaturated hydrocarbons
Aliphatic Saturated Hydrocarbons
Aliphatic saturated hydrocarbons are those compounds which-
  1. Which are aliphatic, that is, in which all the chains present in the atoms are open,
  2. Which are saturated i.e. in which all the four valencies of each carbon atom present are satisfied by single bonds, and
  3. In which only carbon and hydrogen are present, no other elements are present.
  4. These compounds are also called alkanes. Since these compounds are less reactive than other organic compounds, they are also called paraffins (reactivity). These compounds have the general formula CnH2n+2 and are members of the same homologous series.
In this series all the members following propane show isomerism. In the above list only the names of straight chain compounds have been included.

            H                           H     H
             |                             |       |
   H一  C 一H           H一 C一 C一 H         OR        CH3-CH3
             |                             |       |                      
            H                           H     H                            
     
      methane                                        Ethene 
            
Aliphatic Unsaturated Hydrocarbons
Those compounds are called aliphatic unsaturated hydrocarbons which-
  1. Which are aliphatic i.e. in which all the chains of present atoms are open,
  2. which are unsaturated i.e. contain at least one carbon-carbon double bond or carbon-carbon triple bond, and
  3. In which only carbon and hydrogen elements are present.
Those aliphatic unsaturated hydrocarbons which contain only one carbon-carbon double bond are called alkenes. Those aliphatic unsaturated hydrocarbons which contain only one carbon-carbon triple bond are called alkynes.

Alkenes - Those aliphatic unsaturated hydrocarbons in which only one carbon-carbon double bond is present are called alkenes. The general formula of alkenes is CnH2n and all alkenes are members of the same homologous series. Replacing n with 1 in the general formula CnH2n gives the formula CH2. All the four valencies of carbon are not satisfied in this formula. Hence it does not show any compound. It exhibits a bivalent free radical named methylene radical. It is temporary. Two methylene radicals combine to form a molecule of ethylene (C2H4). The simplest member of this series is ethylene (C2H4).

Structural Formula of Ethylene-    CH2 = CH2

This compound reacts with chlorine to form the oily substance ethylene di-chloride. Hence the members of this category are also called olefins (olefiant = oil maker). The double bonds present in olefins are also called olefinic bonds.

Alkynes – Those aliphatic unsaturated hydrocarbons in which only one carbon-carbon triple bond is present are called alkynes. The general formula of alkynes is CnH2n-2 and all alkynes are members of the same homologous series. In the general formula CaH2n-2, the formula (sign) obtained by keeping the value of n as 1 is C. This is the symbol of the carbon atom, so it does not represent any compound. The simplest member of this series is acetylene (C2H2).

Structural Formula of Acetylene- CH ≡ CH   or   H 一 C ≡ C 一H

The triple bonds present in alkynes are also called acetylenic bonds.

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