Question

The correct IUPAC name of

• A. 4-Ethyl-1-Fluoro-2-nitrobenzene
• B. 1-Ethyl-4-Fluoro-3-nitrobenzene
• C. 3-Ethyl-6-Fluoronitrobenzene
• D. 5-Ethyl-2-Fluoronitrobenzene

Answer 1

The Correct Option is A

1. Identify the substituents on the benzene ring
The substituents on the benzene ring are:

- Ethyl ($-C_2H_5$)
- Fluoro ($-F$)
- Nitro ($-NO_2$)

2. Apply IUPAC Nomenclature Rules

- Numbering: The substituents should be numbered to give the lowest possible set of numbers. The priority of numbering is generally based on alphabetical order.

- Alphabetical Order: When naming the compound, the substituents are listed in alphabetical order.

Following these rules, the ethyl group will have a lower number.
Considering the order Fluoro, then Nitro is best.

3. Determine the correct numbering
If we start numbering from the Fluoro group, we have F at 1, $NO_2$ at 2, and ethyl at 4, giving us 1-Fluoro, 2-Nitro, 4-Ethyl.
If we start numbering such that ethyl gets number 1, we have Ethyl at 4, F at 1 and $NO_2$ at 2, giving us 4-Ethyl, 1-Fluoro, 2-Nitro.
According to alphabetical order and priority, it should be numbered such that numbering starts from the Fluoro group.

The molecule follows alphabetical order - Ethyl, Fluoro, Nitro.
We assign the lowest locant to Fluoro i.e., '1'.
The IUPAC name would then be 4-Ethyl-1-Fluoro-2-nitrobenzene.

Final Answer:
(A) 4-Ethyl-1-Fluoro-2-nitrobenzene

Answer 2

To name this compound, follow the IUPAC nomenclature rules:

1. Identify the parent structure: The parent structure is a benzene ring, as the compound contains a benzene ring.
2. Number the positions on the benzene ring: Begin numbering the ring from the position of the highest priority substituent. The highest priority substituent here is the nitro group (NO₂), which is assigned position 1.
3. Number the other substituents: The next priority substituent is the fluorine atom (F), which is placed in position 2. The ethyl group (C₂H₅) is placed in position 4.
4. The correct IUPAC name is: 4-Ethyl-1-Fluoro-2-nitrobenzene.

The correct answer is (A) : 4-Ethyl-1-Fluoro-2-nitrobenzene.