13.6 CLASSIFICATION OF ORGANIC COMPOUNDS

There are millions of organic compounds. It is not possible to study each compound separately. To facilitate learning, they are divided into different groups and sub-groups. It is useful to choose those compounds with a similar structure. So here you will learn the classification of organic compounds based on the carbon skeleton. They are broadly divided into two main groups:

DO YOU KNOW

Alkyl radical contains one less hydrogen than its parent alkane.

(1) Open Chain Compounds

Open chain compounds contain an open chain of carbon atoms. In these compounds, carbon atoms are linked in a linear pattern. For instance:

Propane
CH₃-CH₂-CH₃

Butane
CH₃-CH₂-CH₂-CH₃

Is the compound having the following structure an open chain compound?
CH₂-CH₂-CH₂-CH₂

Open chain compounds may be either straight-chain or branched-chain. Those compounds which contain any number of carbon atoms joined one after the other in a chain or row are called straight chain compounds. In these compounds, carbon atoms are connected in one continuous chain.

Examples:
Propane
CH₃-CH₂-CH₃

Butane
CH₃-CH₂-CH₂-CH₃

Pentane
CH₃-CH₂-CH₂-CH₂-CH₃

Those compounds which contain carbon atoms on the sides of the chain are called branched chain compounds. In these compounds, branches of carbon atoms are attached to a chain of carbon atoms. Which of the following is a branched chain compound?
CH₃-CH(CH₃)-CH₂-CH₃
CH₃-CH₂-CH₂-CH₃
CH₃-CH-CH₃

Open chain compounds are also called alicyclic compounds.

(2) Closed Chain or Cyclic Compounds

Organic compounds which contain rings of atoms are called closed chain or cyclic compounds. For example:

Cyclopropane
CH₃-CH₂-CH₂

Cyclobutane
CH₂-CH₂-CH₂-CH₂

Cyclohexane
CH₃-CH₂-CH₂-CH₂-CH₂-CH₂

Benzene
C₆H₆

Cyclic compounds which contain rings of carbon atoms are called homocyclic or carbocyclic compounds. Which of the above cyclic compounds are carbocyclic? Cyclic compounds that contain one or more atoms other than carbon atoms in the ring are called heterocyclic compounds:

CONCEPT ASSESSMENT EXERCISE 13.4

A to E are the structural formulas of some organic compounds.

Structural Formulas

Give the letters which represent:

  1. A branched chain compound.
  2. A cyclic compound.
  3. Two straight chain compounds.