Which of the aldehyde is most reactive ?

Options

A. `C_(6) H_(5) - `CHO
B. `CH_(3)` CHO
C. HCHO
D. All of these are equally reactive

Explanation

To determine which aldehyde is the most reactive, we need to analyze the structures of the given aldehydes and understand how substituents affect their reactivity. Aldehydes have a carbonyl group (C=O) that is polar, making the carbon atom electron-deficient and susceptible to nucleophilic attack.

### Step-by-Step Solution:

1. **Identify the Aldehydes**: The given aldehydes are:
- Benzaldehyde (C6H5CHO)
- Acetaldehyde (CH3CHO)
- Formaldehyde (HCHO)

2. **Understand the Structure**: The general structure of an aldehyde is RCHO, where R can be a hydrogen atom or an alkyl group. The carbonyl carbon is electrophilic due to the electronegativity of oxygen.

3. **Analyze Electron-Donating Effects**:
- **Benzaldehyde**: The phenyl group (C6H5) is a resonance donor, which means it can donate electron density to the carbonyl carbon, reducing its electrophilicity.
- **Acetaldehyde**: The methyl group (CH3) is an electron-donating group (through +I effect), which also decreases the electron deficiency of the carbonyl carbon.
- **Formaldehyde**: This has two hydrogen atoms attached to the carbonyl carbon, with no electron-donating groups. Thus, it retains a higher degree of electron deficiency.

4. **Determine Reactivity**:
- The more electron-deficient the carbonyl carbon, the more reactive the aldehyde will be towards nucleophilic attack.
- Since formaldehyde has no electron-donating groups, it is the most electron-deficient among the three aldehydes.

5. **Conclusion**: Therefore, **Formaldehyde (HCHO)** is the most reactive aldehyde due to the absence of any electron-donating groups that would reduce the electrophilicity of the carbonyl carbon.

### Final Answer:
**Formaldehyde (HCHO) is the most reactive aldehyde.**

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