Arrange reactivity of given carboxylic acids for esterification reaction in decreasing order
1. HCOOH
2. `CH_3CH_2COOH`
3. `CH_3-underset(CH_3)underset(|)(CH)-COOH`
4. `CH_3- underset(CH_3)underset(|)overset(CH_3)overset(|)C-COOH`

Options

A. 4,3,2,1
B. 1,2,3,4
C. 3,4,2,1
D. 2,3,4,1

Answer

To arrange the reactivity of the given carboxylic acids for the esterification reaction in decreasing order, we need to consider the electrophilicity of the carbonyl carbon in each carboxylic acid. The more electrophilic the carbonyl carbon, the more reactive it will be in the esterification reaction.

### Step-by-Step Solution:

1. **Identify the Carboxylic Acids**:
- 1. HCOOH (Formic acid)
- 2. CH3CH2COOH (Propanoic acid)
- 3. CH3C(CH3)(COOH) (2-Methylpropanoic acid)
- 4. CH3C(CH3)2COOH (3-Methylbutanoic acid)

2. **Analyze Electrophilicity**:
- **Formic Acid (HCOOH)**: The carbonyl carbon has no alkyl groups attached, which means it has the highest electrophilicity. The hydrogen atom does not donate electron density, making the carbon more electron-deficient and thus more reactive.
- **Propanoic Acid (CH3CH2COOH)**: The presence of one alkyl group (ethyl) will slightly reduce the electrophilicity of the carbonyl carbon due to the +I (inductive) effect, but it is still more electrophilic than the others.
- **2-Methylpropanoic Acid (CH3C(CH3)(COOH))**: This compound has two alkyl groups (one ethyl and one methyl). The +I effect from these groups will further decrease the electrophilicity of the carbonyl carbon compared to propanoic acid.
- **3-Methylbutanoic Acid (CH3C(CH3)2COOH)**: This compound has three alkyl groups attached to the carbonyl carbon. The +I effect is maximized here, making the carbonyl carbon the least electrophilic and thus the least reactive in esterification.

3. **Order of Reactivity**:
- Based on the analysis, we can arrange the carboxylic acids in decreasing order of reactivity for esterification:
- **Most Reactive**: HCOOH (Formic acid)
- **Second**: CH3CH2COOH (Propanoic acid)
- **Third**: CH3C(CH3)(COOH) (2-Methylpropanoic acid)
- **Least Reactive**: CH3C(CH3)2COOH (3-Methylbutanoic acid)

4. **Final Arrangement**:
- The final order of reactivity for esterification is:
1. HCOOH
2. CH3CH2COOH
3. CH3C(CH3)(COOH)
4. CH3C(CH3)2COOH