Metamerism and Ring Chain Isomerism

Isomerism of Class 11


This type of isomerism is due to the unequal distribution of carbon atoms on either side of the multivalent functional group (i.e. –O-,-S-,-NH-, –CO- etc.) in the molecule of compounds belonging to the same class. For example, methyl propyl ether and diethyl ether both have same molecular  formula 

(a)        CH3CH2COCH2CH3            is a metamer of     CH3COCH2CH2CH3

                   Pentan-3-one                                                  Pentan-2-one

(b) CH3-O-CH2CH2CH3            is a metamer of     CH3CH2O-CH2CH3

              Methoxy propane                                                      Ethoxy ethane

             (Methyl n-propyl ether)                                              (Diethyl ether)

(c)  CH3CH2-NH-CH2CH3          is a metamer of     CH3-NH-CH2CH2CH3

            Diethyl amine                                                (Methyl n-propyl amine)

Ring-Chain Isomerism

Compounds having same molecular formula but possessing open chain and cyclic structures are called ring-chain isomers and the phenomenon is called ring-chain isomerism.

Degree of Unsaturation

Deficiency of two hydrogen atoms in a molecule is a result of either a pi-bond or a ring in the structure of that molecule. The sum of pi-bonds and rings in the structure of a compound collectively is called degree of unsaturation or double bond equivalents in that compound. The most general type of formula for any organic species is (CaHbNcOd).

If the compound contains other atoms also, the tetravalent atoms are replaced by carbon, monovalent atoms are replaced by hydrogen, divalent atoms are replaced by oxygen and trivalent atoms are replaced by nitrogen. Then all oxygen and all nitrogen atoms are removed from the formula. However, for the removal of each N atom, one H atom is removed from the molecular formula. As a result of all these operations, we will get a hydrocarbon. Now this concluded hydrocarbon is compared with saturated alkane to determine the degree of unsaturation or double bond equivalents.

Talk to Our counsellor