Which of the following names of alcohols is correct according to the IUPAC system?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2-Methylcyclopentanol
A cyclic alcohol is named with the prefix cyclo, and the carbon carrying the –OH group is taken as C-1. In 2-methylcyclopentanol the –OH group is on C-1 of a five-membered ring and the methyl group is on the next carbon, C-2, so the name follows the rules.
Why the other options are incorrect
Option (1) 2-Methylbutan-3-ol — Incorrect.
The compound is CH3CH(CH3)CH(OH)CH3. The chain must be numbered from the end nearest to the –OH group, which puts –OH on C-2 and the methyl group on C-3.
The correct name is 3-methylbutan-2-ol.
Option (2) Ethan-1,2-diol — Incorrect. In a polyhydric alcohol the ‘e’ of the alkane is kept before ‘diol’ or ‘triol’. HO–CH2–CH2–OH is ethane-1,2-diol.
Option (4) 2-Ethylpropan-1-ol — Incorrect. The compound is HOCH2CH(CH2CH3)CH3. Its longest chain has four carbon atoms, not three, so it is named as a butanol: 2-methylbutan-1-ol.
NCERT (2026-27 edition):
7.2 Nomenclature – “According to IUPAC system, the name of an alcohol is derived from the name of the alkane from which the alcohol is derived, by substituting ‘e’ of alkane with the suffix ‘ol’. The position of substituents are indicated by numerals. For this, the longest carbon chain (parent chain) is numbered starting at the end nearest to the hydroxyl group. … For naming polyhydric alcohols, the ‘e’ of alkane is retained and the ending ‘ol’ is added.”
“Cyclic alcohols are named using the prefix cyclo and considering the —OH group attached to C–1.”
