Question

Find the number of structural isomers possible for hexane ?

• A. Two
• B. Four
• C. Three
• D. Five

Hint:

Draw the longest chain first, then shorten it by one carbon and place a methyl at different spots, and so on.

Answer 1

The Correct Option is D

Step 1: Understand the question
Hexane has the molecular formula \(\text{C}_6\text{H}_{14}\). We count every different carbon skeleton that fits this formula, that is, the chain isomers.

Step 2: Six-carbon and five-carbon chains
Chain of 6 carbons: n-hexane. Chain of 5 carbons with one methyl: the methyl can be on C2 (2-methylpentane) or on C3 (3-methylpentane). A methyl on C1 would just extend the chain, so it is not new.

Step 3: Four-carbon chains
Chain of 4 carbons with two methyl groups: both on C2 give 2,2-dimethylbutane, and one on C2 and one on C3 give 2,3-dimethylbutane. Other placements repeat these or lengthen the chain.

Step 4: Count
n-Hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane make 5. A three-carbon chain cannot hold six carbons without repeating the earlier structures. So the answer is five.

Final Answer:
Hexane has five structural isomers, counting itself. This is option (D). \[ \boxed{\text{(D) }5} \]