Which of the following IUPAC name is incorrect ?

Options

A. Ethanoic acid
B. Ethanal
C. Pent-3-yne
D. 3-Methylpentan-2-ol

Answer

To determine which IUPAC name is incorrect, we will analyze each option step by step.

### Step 1: Analyze Ethanoic Acid
- **Structure**: Ethanoic acid has the structure CH3COOH.
- **IUPAC Name**: The IUPAC name is indeed ethanoic acid.
- **Conclusion**: This name is correct.

### Step 2: Analyze Ethanol
- **Structure**: Ethanol has the structure CH3CH2OH.
- **IUPAC Name**: The IUPAC name is ethanol.
- **Conclusion**: This name is correct.

### Step 3: Analyze Pent-3-yne
- **Structure**: The structure given is CH3CH2C≡CCH3.
- **IUPAC Name**: The name pent-3-yne suggests that the triple bond is at the third carbon.
- **Correct Numbering**: According to the lowest sum rule, the correct numbering should be:
- 1: C≡C (triple bond)
- 2: CH2
- 3: CH2
- 4: CH
- 5: CH3
- **Correct Name**: The correct IUPAC name should be pent-2-yne, as the triple bond is between the second and third carbon.
- **Conclusion**: This name is incorrect.

### Step 4: Analyze 3-Methylpentan-2-ol
- **Structure**: The structure should have a hydroxyl (OH) group and a methyl group.
- **IUPAC Name**: The name 3-methylpentan-2-ol indicates that the OH group is on the second carbon and a methyl group is on the third carbon.
- **Correct Numbering**: The numbering should be:
- 1: OH
- 2: CH2
- 3: CH
- 4: CH2
- 5: CH3
- **Conclusion**: This name is correct.

### Final Conclusion
The incorrect IUPAC name among the options is **C: Pent-3-yne**.

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