Which of the following IUPAC names is correct ?

Options

A. 2-Methyl-3-ethylpentane
B. 3-Ethyl-2-methylpentane
C. 2-Ethyl-3-methylpentane
D. 3-Methyl-2-ethylpentane.

Explanation

To determine which of the provided IUPAC names is correct, we need to analyze each name based on the IUPAC nomenclature rules. Here’s a step-by-step breakdown of the solution:

### Step 1: List the Given Names
The names provided are:
1. 2-methyl, 3-ethyl, pentane
2. 3-methyl, 2-methyl, pentane
3. 2-ethyl, 3-methyl, pentane
4. 3-ethyl, 2-methyl, pentane

### Step 2: Identify the Longest Carbon Chain
In all cases, we are dealing with pentane, which indicates a 5-carbon chain. However, we need to check if there are longer chains possible in the structures implied by the names.

### Step 3: Analyze Substituents
The substituents in the names are:
- Methyl (–CH₃)
- Ethyl (–C₂H₅)

### Step 4: Determine the Correct Order of Substituents
According to IUPAC rules, when naming compounds with multiple substituents, they should be listed in alphabetical order regardless of their position on the carbon chain.

- Ethyl (E) comes before Methyl (M) alphabetically.

### Step 5: Evaluate Each Name
1. **2-methyl, 3-ethyl, pentane**: Incorrect because ethyl should come before methyl.
2. **3-methyl, 2-methyl, pentane**: Incorrect because it has two identical substituents and does not follow the alphabetical order.
3. **2-ethyl, 3-methyl, pentane**: Incorrect because it does not follow the alphabetical order (methyl should come after ethyl).
4. **3-ethyl, 2-methyl, pentane**: Correct because it follows the alphabetical order (ethyl before methyl).

### Conclusion
The correct IUPAC name among the options provided is **3-ethyl, 2-methyl, pentane**.

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