The order of reactivity of carbonyl compounds for nucleophilic addition is

Options

A. `Ar_(2)C=OgtR_(2)C=OgtArCHOgtRCHOgtH_(2)C=O`
B. `H_(2)C=OgtR_(2)C=OgtAr_(2)C=OgtRCHOgtArCHO`
C. `H_(2)C=OgtRCHOgtArCHOgtR_(2)C=OgtAr_(2)C=O`
D. `ArCHOgtAr_(2)C=OgtRCHOgtR_(2)C=OgtH_(2)C=O`

Answer

To determine the order of reactivity of carbonyl compounds for nucleophilic addition, we need to analyze the electrophilicity of the carbonyl carbon in different compounds. The more electrophilic the carbonyl carbon, the more reactive it is towards nucleophiles.

### Step-by-Step Solution:

1. **Understanding Nucleophilic Addition**:
- Nucleophilic addition involves a nucleophile attacking an electrophilic carbon atom in a carbonyl group (C=O). The carbonyl carbon is electrophilic due to the electronegativity of oxygen, which pulls electron density away from the carbon.

2. **Identifying the Compounds**:
- The compounds given are:
- A: Ar2CO (e.g., diphenyl ketone)
- B: R2CO (e.g., acetone)
- C: ArCHO (e.g., benzaldehyde)
- D: RCHO (e.g., acetaldehyde)
- E: H2CO (e.g., formaldehyde)

3. **Evaluating Electrophilicity**:
- **Formaldehyde (H2CO)**: The carbonyl carbon is highly electrophilic because it is not stabilized by any electron-donating groups. Thus, it is the most reactive.
- **Acetaldehyde (RCHO)**: The methyl group (CH3) donates electron density through the inductive effect, making it less electrophilic than formaldehyde but more electrophilic than benzaldehyde.
- **Benzaldehyde (ArCHO)**: The phenyl group can donate electron density through resonance, which decreases the electrophilicity of the carbonyl carbon, making it less reactive than acetaldehyde.
- **Acetone (R2CO)**: The two methyl groups donate electron density through the inductive effect, further decreasing electrophilicity compared to benzaldehyde.
- **Diphenyl Ketone (Ar2CO)**: The presence of two phenyl groups significantly decreases the electrophilicity of the carbonyl carbon due to resonance donation from both rings, making it the least reactive.

4. **Order of Reactivity**:
- Based on the analysis of electrophilicity:
1. **Formaldehyde (H2CO)** - Most reactive
2. **Acetaldehyde (RCHO)**
3. **Benzaldehyde (ArCHO)**
4. **Acetone (R2CO)**
5. **Diphenyl Ketone (Ar2CO)** - Least reactive

### Final Order of Reactivity:
**H2CO > RCHO > ArCHO > R2CO > Ar2CO**