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: Method
List skeletons by the length of the longest chain, from long to short.

Step 2: Longest chain 6
Only one: $\text{CH}_3(\text{CH}_2)_4\text{CH}_3$.

Step 3: Longest chain 5
One extra carbon as a methyl branch on carbon 2 or carbon 3. These two are different molecules (carbon 4 is the same as carbon 2 by symmetry).

Step 4: Longest chain 4
Two methyl branches: $(\text{CH}_3)_3\text{C-CH}_2\text{CH}_3$ and $(\text{CH}_3)_2\text{CH-CH}(\text{CH}_3)_2$. Chain of 3 is impossible with only a methyl or ethyl branch without lengthening. Total: $1 + 2 + 2 = 5$.

Final Answer:
The five isomers of $\text{C}_6\text{H}_{14}$ include hexane. This is option (D). \[ \boxed{\text{(D) }5} \]