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 types of carbonyl compounds. The carbonyl compounds we will consider include aldehydes, ketones, and aromatic carbonyl compounds.

### Step-by-Step Solution:

1. **Understanding Nucleophiles and Electrophiles**:
- Nucleophiles are species that have a negative charge or a lone pair of electrons and can donate electrons to electrophiles, which are electron-deficient species.
- In carbonyl compounds, the carbon atom of the carbonyl group (C=O) is electrophilic due to the partial positive charge (δ+) it carries.

2. **Analyzing Different Carbonyl Compounds**:
- **Aldehydes (RCHO)**: The carbonyl carbon in aldehydes is attached to one alkyl group (R) and one hydrogen atom (H). The hydrogen does not exert a +I (inductive) effect, making the carbonyl carbon more electrophilic.
- **Ketones (RC(=O)R')**: In ketones, the carbonyl carbon is bonded to two alkyl groups (R and R'). The presence of two alkyl groups increases the +I effect, which reduces the electrophilicity of the carbonyl carbon compared to aldehydes.
- **Aromatic Carbonyl Compounds (ArC(=O)R)**: In compounds like aromatic aldehydes (ArCHO) or aromatic ketones (ArC(=O)R), the aromatic ring exerts a +R (resonance) effect, which can delocalize the electron density away from the carbonyl carbon, making it less electrophilic.

3. **Comparing Reactivity**:
- Aldehydes are generally more reactive than ketones because the carbonyl carbon in aldehydes is more electrophilic due to the presence of only one alkyl group and one hydrogen atom.
- Among aromatic carbonyl compounds, the presence of the aromatic ring decreases the electrophilicity of the carbonyl carbon due to resonance effects. Therefore, aromatic aldehydes are less reactive than aliphatic aldehydes, and aromatic ketones are less reactive than aliphatic ketones.

4. **Order of Reactivity**:
- Based on the above analysis, we can establish the order of reactivity for nucleophilic addition as follows:
- Aldehydes (RCHO) > Ketones (RC(=O)R) > Aromatic Aldehydes (ArCHO) > Aromatic Ketones (ArC(=O)R)

### Final Order of Reactivity:
**Aldehydes > Ketones > Aromatic Aldehydes > Aromatic Ketones**