What is the correct IUPAC name of the compound? [figure]
- 1-Ethylcyclopent-2-en-3-ol
- 4-Ethylcyclopent-2-en-1-ol
- 1-Ethyl-3-hydroxycyclopent-2-ene
- 4-Ethyl-1-hydroxycyclopent-2-ene
Answer
(2) 4-Ethylcyclopent-2-en-1-ol
Solution
Principal functional group: –OH (suffix "-ol"), so the ring carbon carrying –OH is C-1.
Number the ring from C-1 towards the double bond so that the C=C gets the lowest locants: C-2 = C-3.
The ethyl group is then on C-4.
Parent: cyclopentene (five-membered ring with one C=C) cyclopent-2-en-1-ol.
IUPAC name: 4-Ethylcyclopent-2-en-1-ol.
(Options (3) and (4) wrongly write –OH as the prefix "hydroxy"; option (1) does not give –OH the lowest locant.)
Answer: (2)