Which of the following IUPAC Name is conceptually incorrect?

Options

A. `2-`Ethylpentane
B. `5-`Ethyl`-3-`Methyl heptane
C. `2,4` diethylpentane
D. All of these

Explanation

To determine which of the given IUPAC names is conceptually incorrect, we will analyze each name step by step.

### Step 1: Analyze 2-ethylpentane
1. **Identify the longest carbon chain**: The name "2-ethylpentane" suggests a five-carbon chain (pentane) with an ethyl group at the second position.
2. **Draw the structure**:
- The five-carbon chain is:
```
CH3-CH-CH2-CH2-CH3
|
CH2-CH3
```
- This structure indicates a branching at the second carbon.
3. **Check for longer chains**:
- If we start numbering from the leftmost carbon, we can see that the longest chain actually has six carbons (including the ethyl group).
- The correct name should be "3-methylhexane" instead of "2-ethylpentane".

**Conclusion for Step 1**: The name "2-ethylpentane" is conceptually incorrect.

### Step 2: Analyze 5-ethyl-3-methylheptane
1. **Identify the longest carbon chain**: The name "5-ethyl-3-methylheptane" suggests a seven-carbon chain (heptane) with an ethyl group at the fifth position and a methyl group at the third position.
2. **Draw the structure**:
- The seven-carbon chain is:
```
CH3-CH2-CH-CH2-CH-CH2-CH3
| |
CH3 CH2-CH3
```
3. **Check for correct numbering**:
- When numbering from the left, the ethyl group should take priority due to its larger size, and the correct numbering would actually place the ethyl group at the third position.
- The correct name should be "3-ethyl-5-methylheptane".

**Conclusion for Step 2**: The name "5-ethyl-3-methylheptane" is also conceptually incorrect.

### Step 3: Analyze 2,4-Diethylpentane
1. **Identify the longest carbon chain**: The name "2,4-Diethylpentane" suggests a five-carbon chain (pentane) with ethyl groups at the second and fourth positions.
2. **Draw the structure**:
- The five-carbon chain is:
```
CH3-CH-CH2-CH-CH3
| |
CH2-CH3 CH2-CH3
```
3. **Check for longer chains**:
- If we consider the structure, we can see that there is a longer chain available (7 carbons) when we include the ethyl groups.
- The correct name should be "3,5-Diethylheptane".

**Conclusion for Step 3**: The name "2,4-Diethylpentane" is also conceptually incorrect.

### Final Conclusion
All three given IUPAC names are conceptually incorrect. The correct names based on the longest carbon chains and proper substituent placement should be:
- 2-ethylpentane should be 3-methylhexane.
- 5-ethyl-3-methylheptane should be 3-ethyl-5-methylheptane.
- 2,4-Diethylpentane should be 3,5-Diethylheptane.

### Answer: All of the given names are conceptually incorrect.

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