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Anuvrat Kulkarni Grade:

Thank you....... How do we calculate no. of Chain, Position, Metamerism, Tautomerism? please tell me formula

7 years ago

Answers : (1)

879 Points

Dear anuvrat,

Chain isomerism

This type of isomerism arises from the difference in the nature, structure of the carbon chain. For example, for butane (C4H10), the following arrangements are possible.

butane in straight chain

iso butane in branched chain

Pentane (C5H12) exhibits the following three structures.

structures of pentane


Butanol (butyl alcohol) has the following two structures of the carbon chain.

structures of butanol


For butanal, (C3H7CHO), the following chain isomers are possible.

chain isomers of butanal


Position isomerism

This isomerism arises due to the difference in the position of the same functional group or the same substituent while the arrangement of carbon atoms remains same. For example,

Chloropropane (C3H7Cl) can have two positional isomers given below.


positional isomers of chloropropane



Butene (C4H8) can have two positional isomers.


positional isomers of butene



Propanol (C3H7OH) has the following positional isomers.


positional isomers of propanol



Functional isomerism

The compounds having the same molecular formula but different functional groups are said to exhibit functional isomerism. Such compounds are termed functional isomers. For example, there are two compounds having the molecular formula C2H6O viz.,



functional isomers of C2H6O



The molecular formula C3H6O represents two functional isomers.


functional isomers of C3H6O



This type of isomerism arises from the unequal distribution of carbon atoms on either side of the functional group in the molecule of compounds belonging to the same homologous series. For example, diethyl ether and methylpropyl ether are metamers.

diethyl ether and methylpropyl ether are metamers

A ketonic compound having the molecular formula C5H10O, has the following two metamers.

metamers of C5H10O


This is a special case of functional isomerism. Certain substances can

exhibit properties of two functional groups as for instance, acetoacetic ester behaves like a ketone as well as an alcohol. This arises due to the migration of a labile hydrogen atom from one place to another.In acetoacetic ester, the inter-conversion between keto and enolic group takes place as follows.


inter-conversion between keto and enolic group


In amides, it happens as follows:


keto-enol tautomerisn in amides


Both these forms of the same molecule exist in equilibrium in a sample of compound. The migration of a labile hydrogen between two polyvalent atoms in the same molecule causes this type of dynamic isomerism. This is termed as tautomerism or keto-enol tautomerisn. Such isomers are termed as tautomers.


Please feel free to ask your queries here. We are all IITians and here to help you in your IIT JEE preparation.

All the best.

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Askiitians Expert

Sagar Singh

B.Tech, IIT Delh

7 years ago
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