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

Step 1: Write the molecular formula of both compounds. CH₃CHCl₂ has 2 carbons, 4 hydrogens and 2 chlorines, so its formula is C₂H₄Cl₂. CH₂Cl-CH₂Cl also has 2 carbons, 4 hydrogens and 2 chlorines, so it is also C₂H₄Cl₂. Same molecular formula means the two are isomers of each other.

Step 2: Look at where the two chlorine atoms sit on the carbon chain. In CH₃CHCl₂, both chlorine atoms are attached to the same carbon, this is 1,1-dichloroethane. In CH₂Cl-CH₂Cl, one chlorine is on each carbon, this is 1,2-dichloroethane.

Step 3: When two compounds have the same carbon skeleton and the same functional group but the position of the substituent differs on that skeleton, the isomerism is called positional isomerism. Here the carbon chain is the same, a straight 2 carbon chain, and the substituent is chlorine in both, only its position changes.

Step 4: This rules out chain isomerism, which needs different carbon skeletons, functional group isomerism, which needs different functional groups such as an alcohol versus an ether, and metamerism, which needs different alkyl groups on either side of the same functional atom, typically seen in ethers, amines and thioethers. So the correct answer is positional isomerism, option C.