Question

The type of isomerism that exists between CH₃CHCl₂ and CH₂Cl-CH₂Cl is:

• A. Chain isomerism
• B. Functional group isomerism
• C. Positional isomerism
• D. Metamerism

Hint:

Both compounds share the same formula; only the placement of chlorine on the chain differs.

Answer 1

The Correct Option is C

Compare the two structures atom by atom.

1. Both molecules contain 2 carbon atoms, 4 hydrogen atoms and 2 chlorine atoms, giving the same molecular formula $C_2H_4Cl_2$, so they qualify as isomers.
2. In the first structure, $CH_3CHCl_2$, one carbon carries both chlorine atoms and the other carbon carries three hydrogens.
3. In the second structure, $CH_2Cl-CH_2Cl$, the two chlorine atoms are spread out, one on each carbon.
4. The parent chain, ethane, and the substituent, chlorine, are identical in both cases. Only the location of chlorine on the chain has changed, which is the defining feature of positional isomerism.
5. Chain isomerism would need a different arrangement of carbon atoms, and metamerism applies to compounds like ethers or amines with different alkyl groups around a central atom, neither of which fits here.
6. Hence the answer is option C, positional isomerism.