JEE Main 2025 · 8 April · evening · Single correct · +4 / −1
What is the correct IUPAC name of the compound?
- (a) 1-Ethylcyclopent-2-en-3-ol
- (b) 4-Ethylcyclopent-2-en-1-ol
- (c) 1-Ethyl-3-hydroxycyclopent-2-ene
- (d) 4-Ethyl-1-hydroxycyclopent-2-ene
Answer and solution
Answer (b) 4-Ethylcyclopent-2-en-1-ol
Solution
Chemistry ma’am · 4 steps
The OH is the boss here: give its carbon number 1, then run towards the double bond.
- Principal group. The ring carries an -OH group, a C=C double bond and an ethyl group. Of these, -OH has the highest priority, so it is named as the suffix -ol and its carbon gets locant 1.
- Choose the direction. From C1 you can number the ring two ways. The next rule is that the double bond gets the lowest possible locant.
Direction from C1 Double bond at Ethyl at Towards the double bond C2 = C3, locant 2 C4 Towards the CH₂ C4 = C5, locant 4 C3 - Build the name. With the first direction, the parent is cyclopent-2-en-1-ol and the ethyl group sits on C4. Substituent prefixes come before the parent name.
- So. The compound is 4-ethylcyclopent-2-en-1-ol, which is option (b).
The idea to keep. In a ring, the carbon with the principal group is always C1. Then number in the direction that gives the double bond the lowest locant, and only after that look at the substituents.
Answer from the NTA final answer key. Solution by PrepWiser.