Which isomerism is shown by the following pairs?
\(CH_3CH_2CH_2OH\) and \(CH_3CH_2OCH_3\)
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Functional isomerism
Both compounds have the molecular formula C3H8O:
\( \ce{CH3CH2CH2OH} \) is propan-1-ol, an alcohol (–OH group).
\( \ce{CH3CH2OCH3} \) is methoxyethane, an ether (C–O–C group).
Compounds with the same molecular formula but different functional groups are functional (functional group) isomers. Alcohols and ethers of the same formula are a standard example.
Why the other options are incorrect
Option (1) Position isomerism — Incorrect. Position isomers keep the same functional group at a different position on the chain, e.g. propan-1-ol and propan-2-ol.
Option (3) Structural isomerism — Incorrect. This is the broad class that includes chain, position and functional isomerism; it does not name the specific type shown by an alcohol–ether pair.
Option (4) Chain isomerism — Incorrect. Chain isomers differ in the carbon skeleton (straight or branched) with the same functional group, e.g. butan-1-ol and 2-methylpropan-1-ol.