Which of the following is the correct IUPAC name of the following structure?
A. Chlorocyclopentane
B. 2-Chloro-1-methylcyclopentane
C. 1-Methyl-2-chlorocyclopentane
D. 1-Chloro-2-methylcyclopentane
The Correct Answer and Explanation is
To determine the correct IUPAC name of the given structure, let’s break down the naming rules and apply them step-by-step. Since the image of the structure is not provided, we’ll assume a general structure that this multiple-choice question refers to—typically, a cyclopentane ring substituted with a methyl group (–CH₃) and a chlorine atom (–Cl).
Step 1: Identify the Parent Hydrocarbon
The base structure is cyclopentane, which is a five-membered carbon ring.
Step 2: Identify the Substituents
We are told (or can infer) that there is:
- One chlorine (Cl) substituent
- One methyl (CH₃) substituent
Step 3: Number the Carbon Ring
The rules for numbering a ring in IUPAC naming are:
- Number the ring in a way that gives the lowest possible set of locants to the substituents.
- Alphabetical priority is used only when both substituents could receive the same numbers by numbering in either direction.
Let’s try numbering the ring:
- Start at the carbon bonded to the chlorine atom (Cl) → this becomes carbon 1.
- Then number the ring to give the next substituent (the methyl group) the lowest possible number.
So if the methyl group is attached to the next carbon, it would be at carbon 2.
This gives:
- Chlorine at position 1
- Methyl at position 2
Now apply alphabetical order in naming: “chlorine” comes before “methyl”, so “chloro” is listed before “methyl” in the name.
Correct IUPAC Name:
1-Chloro-2-methylcyclopentane
Answer:
✅ D. 1-Chloro-2-methylcyclopentane
Explanation Summary:
- The parent ring is cyclopentane.
- The ring contains two substituents: a chloro and a methyl group.
- The ring is numbered such that substituents get the lowest locants: Cl at carbon 1, CH₃ at carbon 2.
- Substituents are listed alphabetically in the name.
- Hence, the correct IUPAC name is 1-Chloro-2-methylcyclopentane.
This follows all standard IUPAC nomenclature rules
.