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 determine the reactivity of the given carboxylic acids for esterification reactions in decreasing order, we need to analyze the effects of substituents on the electrophilicity of the carbonyl carbon in each acid. The more electrophilic the carbonyl carbon, the more reactive the acid will be in esterification.

### Step-by-Step Solution:

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

2. **Understand the Esterification Reaction:**
- The esterification reaction involves a carboxylic acid (RCOOH) reacting with an alcohol (R-OH) to form an ester (RC(=O)OR') and water (H2O). The rate of this reaction depends on the electrophilicity of the carbonyl carbon in the carboxylic acid.

3. **Analyze Electrophilicity:**
- Electrophilicity is affected by the presence of electron-donating groups (like alkyl groups) which increase electron density on the carbonyl carbon, making it less electrophilic and thus less reactive.
- HCOOH has no substituents, making it the most electrophilic.
- CH3CH2COOH has one alkyl group (ethyl), which will slightly decrease electrophilicity.
- CH3C(CH3)2COOH has two alkyl groups (isopropyl), which will further decrease electrophilicity.
- CH3C(CH3)3COOH has three alkyl groups (tert-butyl), which will significantly decrease electrophilicity.

4. **Order the Reactivity:**
- Based on the analysis:
- HCOOH (most electrophilic, no substituents)
- CH3CH2COOH (one ethyl group)
- CH3C(CH3)2COOH (two methyl groups)
- CH3C(CH3)3COOH (three methyl groups, least electrophilic)

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