Question

Identify the correct option in which the compound is not named as per IUPAC
(A)

(B)

(C)

(D)

• A. 1-Ethyl-3, 3-dimethyl cyclohexane
• B. Cyclohex-2-en-1-ol
• C. 2-Chloro-1-methyl-4-nitrobenzene
• D. 4-Ethyl-1-fluoro-2-nitrobenzene

Hint:

For disubstituted cycloalkanes, a gem-disubstituted carbon (bearing two substituents) should be assigned locant 1 over a mono-substituted carbon to satisfy the lowest set of locants rule.
This is a common trap in IUPAC nomenclature questions.

Answer 1

The Correct Option is A

Step 1: Focus on the compound in option A.
It is a cyclohexane ring bearing one ethyl group and two methyl groups on the same ring carbon.
Step 2: Apply the lowest-locant rule properly.
Numbering must be chosen so the full set of substituent locants is as low as possible at the first point of difference, comparing the locant set from every possible starting point and direction, not just picking one arbitrary starting carbon.
Step 3: Compare with the name given.
Using the correct lowest-locant numbering, the substituents land on a different locant set than the one quoted in the given name, so that name breaks the IUPAC rule, while the ring systems in the other three options are named correctly with their principal groups getting the lowest locants.
Final answer: Option 1, the cyclohexane compound is the one that is not correctly IUPAC named.