Question

The number of possible structural isomers of $C_3H_6Cl_2$ are

• A. 3
• B. 2
• C. 5
• D. 4
• E. 6

Hint:

For substituted alkanes, first use chain symmetry to avoid counting identical positions twice.

Answer 1

The Correct Option is D

Concept:
Structural isomers have same molecular formula but different connectivity of atoms.
Step 1: Parent carbon chain.
For $C_3H_6Cl_2$, the parent chain is propane with two hydrogen atoms replaced by two chlorine atoms.
Step 2: Write all possible positions of two chlorine atoms.
Distinct arrangements are: \[ 1,1\text{-dichloropropane} \] \[ 1,2\text{-dichloropropane} \] \[ 1,3\text{-dichloropropane} \] \[ 2,2\text{-dichloropropane} \]
Step 3: Check duplicates.
By chain symmetry, no other new arrangement is possible.
Step 4: Total isomers.
\[ \boxed{4} \]
Hence, correct option is (D).