Reactivity of acids in esterification follows the order .

Options

A. `HCO OH gt CH_(3)CO OH gt RCH_(2)CO OH gt R_(2)CHCO OH gt R_(3)C CO OH`
B. `CH_(3)CO OH gt HCO OH gt R_(3)C CO OH gt R_(2) CHCO OH gt RCH_(2)CO OH`
C. `R_(3)C CO OH gt R_(2)CHCO OH gt RCH_(2)CO OH gt CH_(3)CO OH gt HCO OH`
D. None of the above

Answer

To determine the reactivity of acids in esterification, we need to analyze the structure of the acids and how their substituents affect the electron density at the carbonyl carbon. The order of reactivity can be established based on the electron-donating or electron-withdrawing effects of the alkyl groups attached to the carboxylic acid.

### Step-by-Step Solution:

1. **Understanding Esterification**:
Esterification is a reaction between a carboxylic acid (RCOOH) and an alcohol (R'OH) to form an ester (RCOOR') and water. The reaction is typically catalyzed by an acid.

2. **Identifying the Acid Structure**:
The general structure of a carboxylic acid is RCOOH, where R is the alkyl or aryl group. The reactivity in esterification depends on the nature of the R group.

3. **Electron Density at Carbonyl Carbon**:
The carbonyl carbon (C=O) in the carboxylic acid is electrophilic, meaning it is susceptible to nucleophilic attack. The electron density on this carbon can be affected by the substituents (R groups).

4. **Effect of R Groups**:
- Electron-donating groups (like alkyl groups) increase the electron density on the carbonyl carbon, making it less electrophilic and thus less reactive in esterification.
- Conversely, electron-withdrawing groups (like hydrogen in formic acid) decrease the electron density, making the carbonyl carbon more electrophilic and more reactive.

5. **Order of Reactivity**:
- Formic acid (HCOOH) has no alkyl group, making it the most reactive.
- Acetic acid (CH3COOH) has a methyl group, which is weakly electron-donating, making it less reactive than formic acid.
- Butyric acid (C2H5COOH) has an ethyl group, which is more electron-donating than a methyl group, making it even less reactive.
- Propionic acid (C3H7COOH) has a propyl group, further decreasing reactivity.
- Higher alkyl groups (like isobutyric acid) will have even lower reactivity due to increased electron-donating effects.

6. **Final Order of Reactivity**:
The order of reactivity of the acids in esterification is:
- Formic acid (most reactive)
- Acetic acid
- Propionic acid
- Butyric acid
- Higher alkyl acids (least reactive)

Thus, the order of reactivity of acids in esterification follows:
**HCOOH > CH3COOH > C2H5COOH > C3H7COOH > R groups**