(a) Tetravalency Principle of Kekule :
The main points of this principle are given as below :
- Carbon atom shows tetravalency i. e., its valency is four.
- Carbon atom combines with other carbon atoms to form different open chained closed chained compounds.
- Carbon can form single bond, double bond and triple bond with other atoms.
(b) Van’t Hoff and Le Bel’s Principle : According to this principle, “In an organic compound, four valency of carbon is present at the centre of the structure”. Four covalent bonds of carbon form 109°28′ with each other. All the four valency of carbon are same. This theory shows that all the four valencies of carbon are not present in one plane. This theory helps in understanding the study of three dimensional shape of carbon.
(c) Homologous Series : All organic compounds are made up of a progressively building chain of carbon atoms with a number of compounds having the same functional groups. Such a series of similarly constituted compounds are called a homologous series.
Members of a homologous series are similar in structure and exhibit similar chemical characteristics. The two consecutive members of the series differ in their molecular formula by a —CH2— group.
