Question

What are structural isomers? List any four characteristics of isomers. Draw the possible structures of butane.

Answer 1

Isomerism is the phenomenon of existence of two or more compounds possessing the same molecular formula but different chemical and physical properties. Isomerism is broadly of two types, that is, structural isomerism or constitutional isomerism, and stereoisomers.

Complete step by step solution:
Structural isomers are those isomers in which the compounds possessing the same molecular formula differ in their properties due to the difference in the linkage of atoms inside the molecule, i.e., due to a difference in their structures or bonding.
The four main characteristics of isomerism are:

1. They have the same molecular formula but have a different structural formula.
2. Two or more different compounds are represented by the same molecular formula.
3. Isomers of a certain molecular formula differ in their properties.
4. Isomerism is observed only if the hydrocarbon contains four or more carbon atoms.
   There are two possible structural isomers for butane. They are n-butane and isobutane or 2- methyl propane. There structures are as follows:
   

Note:
Structural isomers can be of various sub types namely:

1. Chain isomers: They are different due to a difference in the arrangement of the parent carbon chain present in them. One of them may contain a straight chain while the others may be branched.
2. Positional isomers: They are different due to the difference in the position of the functional group or the multiple bonds or the branched chain attached to the parent carbon chain.
3. Functional isomers: They differ in the functional group present in them. For example an alcohol and an ether have the same molecular formula.
4. Metamers: They differ only in the alkyl groups present and have the same functional group.
5. Tautomers: Tautomers are structural isomers (constitutional isomers) of chemical compounds that readily interconvert.
6. Ring chain isomers: They possess open chain and cyclic structures having the same molecular formula.