Compounds having same molecular formula but different connectivity of atoms or groups are called structure isomers. Structrue isomers are futher classify according to their dissimilarities.
Which is not the isomer of butanoic acid?

Options

A. `3`-Hydroxybutanal
B. Ethyl ethanoate
C. `2`-Methylpropanoic acid
D. Butane-`2,3`-diol

Answer

To determine which compound is not an isomer of butanoic acid, we need to follow these steps:

### Step 1: Identify the molecular formula of butanoic acid.
Butanoic acid has the molecular formula C4H8O2.

### Step 2: Analyze the options provided.
We have the following options:
1. 3-hydroxybutanol
2. Ethyl ethanoate
3. 2-methyl propanoic acid
4. Butane-2,3-diol

### Step 3: Calculate the molecular formulas of the options.
1. **3-hydroxybutanol**:
- Structure: CH3-CH(OH)-CH2-COOH
- Molecular formula: C4H8O2 (Isomer of butanoic acid)

2. **Ethyl ethanoate**:
- Structure: CH3-COO-CH2-CH3
- Molecular formula: C4H8O2 (Isomer of butanoic acid)

3. **2-methyl propanoic acid**:
- Structure: CH3-CH(CH3)-COOH
- Molecular formula: C4H8O2 (Isomer of butanoic acid)

4. **Butane-2,3-diol**:
- Structure: CH3-CHOH-CHOH-CH3
- Molecular formula: C4H10O2 (Not an isomer of butanoic acid)

### Step 4: Compare the molecular formulas.
- The first three options (3-hydroxybutanol, ethyl ethanoate, and 2-methyl propanoic acid) all have the same molecular formula as butanoic acid (C4H8O2).
- The fourth option, butane-2,3-diol, has a different molecular formula (C4H10O2).

### Conclusion:
The compound that is not an isomer of butanoic acid is **butane-2,3-diol**.

### Final Answer:
**Butane-2,3-diol** is not an isomer of butanoic acid.

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