Question

Number of constitutional isomers of alkane with formula $C_6H_{14}$ is

• A. 3
• B. 2
• C. 5
• D. 10
• E. 8

Hint:

There is no simple formula for calculating the number of isomers. The best way is to systematically decrease the main chain length and add branches while avoiding duplicates.

Answer 1

The Correct Option is C

Concept: Constitutional (structural) isomers are compounds with the same molecular formula but different connectivity of atoms. For alkanes, this involves varying the carbon chain length and branching.

Step 1: Identify the possible carbon skeletons.

• n-hexane: A straight chain of six carbons.
• 2-methylpentane: A five-carbon chain with a methyl group on the second carbon.
• 3-methylpentane: A five-carbon chain with a methyl group on the third carbon.
• 2,2-dimethylbutane: A four-carbon chain with two methyl groups on the second carbon.
• 2,3-dimethylbutane: A four-carbon chain with methyl groups on the second and third carbons.

Step 2: Conclusion.
There are exactly 5 distinct structural isomers for hexane.