Select the correct IUPAC name for the cycloalkane:
The IUPAC name is: 1-fluoro-2-(2-methylethyl)cyclopentane
1-(2-methylethyl)-2-fluorocyclopentane
2-isopropyl-1-fluorocyclopentane
1-fluoro-2-(2-methylpropyl)cyclopentane
The Correct Answer and Explanation is:
The correct IUPAC name is: 1-fluoro-2-(2-methylethyl)cyclopentane
Explanation:
To determine the correct IUPAC name for a substituted cycloalkane, we must follow systematic steps outlined by IUPAC naming conventions. Let’s break it down:
1. Identify the Parent Chain:
The parent compound here is a cyclopentane, a five-membered carbon ring.
2. Identify and Name Substituents:
The two substituents are:
- A fluoro group (–F), which is a halogen.
- An alkyl group that looks like CH2–CH(CH3). This is called a 2-methylethyl group (not to be confused with isopropyl or 2-methylpropyl).
Let’s analyze this group more carefully:
- The carbon bonded to the ring is a CH2, attached to a CH (which has a CH3 group).
- This structure matches the name 2-methylethyl.
- It is not isopropyl (CH(CH3)2), and not 2-methylpropyl (CH2CH(CH3)2).
3. Number the Ring to Give the Lowest Set of Locants:
According to IUPAC rules:
- Number the ring so that substituents get the lowest possible numbers.
- The fluoro group has higher alphabetical priority than the alkyl group. Therefore, the carbon with the fluoro group becomes carbon 1.
- This makes the alkyl group on carbon 2.
4. Write the Name:
- Start with the position and name of the fluoro substituent: 1-fluoro.
- Then list the alkyl group: 2-(2-methylethyl).
- Finally, add the parent name: cyclopentane.
So, the correct IUPAC name is:
1-fluoro-2-(2-methylethyl)cyclopentane
Why the Other Options Are Incorrect:
- 1-(2-methylethyl)-2-fluorocyclopentane: Same groups, but not in alphabetical order—fluoro must come first.
- 2-isopropyl-1-fluorocyclopentane: Incorrect group; isopropyl has a different structure.
- 1-fluoro-2-(2-methylpropyl)cyclopentane: Incorrect group; 2-methylpropyl contains an extra carbon.
Conclusion:
The accurate name follows IUPAC rules for alphabetical priority, correct substituent naming, and proper locant assignment:
✅ 1-fluoro-2-(2-methylethyl)cyclopentane