11.1 Organic Compounds (Classification and Characteristics)

11.1.1 Classification of Organic Compounds

All known organic compounds have been broadly divided into two categories depending upon their carbon skeleton. These are:

(i) Open chain or acyclic compounds. (ii) Closed chain or cyclic compounds.

(i) Open chain or Acyclic compounds

Open chain compounds are those in which the end carbon atoms are not joined with each other, in this way they form a long chain of carbon atoms. These chains may be either straight or branched. For example,

(a) Straight chain compounds are those in which carbon atoms link with each other through a single, double or triple bonds forming a straight chain such as;

(b) Branched chain compounds are those in which there is a branch along a straight chain, such as:

Open chain compounds are also called aliphatic compounds.

(ii) Closed chain or Cyclic compounds

Closed chain or cyclic compounds are those in which the carbon atoms at the end of the chain are not free. They are linked to form a ring. They are further divided into two classes:

(a) Homocyclic or carboxylic compounds.

(b) Heterocyclic compounds.

(a) Homocyclic or Carbocyclic compounds.

Homocyclic or carboxylic compounds contain rings which are made up of only one kind of atoms, i.e., carbon atoms. These are further divided into two classes:

Aromatic compounds Alicyclic compounds

Aromatic compounds:

These organic compounds contain at least one benzene ring in their molecule. A benzene ring is made up of six carbon atoms with three alternating double bonds. They are called aromatic because of aroma or smell they have. For example:

They are also called benzenoid compounds.

Alicyclic or non-benzenoic compounds:

Carbocyclic compounds which do not have benzene ring in their molecules are called alicyclic or non- benzenoid compounds. For example,

(b) Heterocyclic compounds

Cyclic compounds that contain one or more atoms other than that of carbon atoms in their rings are called heterocyclic compounds.