Which of the following is most reactive towards nucleophilic addition reactions ?

Options

A. `CH_3 COCH_3`
B. `CH_3 CHO`
C. `CH_3COC_2H_5`
D. `HCHO`

Answer

To determine which of the given compounds is most reactive towards nucleophilic addition reactions, we need to analyze the structure of each compound and the factors that influence the reactivity of carbonyl compounds in such reactions.

### Step-by-Step Solution:

1. **Understanding Nucleophilic Addition**:
- Nucleophilic addition reactions involve the attack of a nucleophile (an electron-rich species) on the electrophilic carbon of a carbonyl group (C=O). The reactivity of carbonyl compounds towards nucleophiles depends on the electrophilicity of the carbon atom, which is influenced by the presence of electron-donating or electron-withdrawing groups.

2. **Analyzing the Given Compounds**:
- Let's denote the compounds as follows:
1. Compound A: R1C(=O)R2 (e.g., CH3C(=O)CH3)
2. Compound B: R3C(=O)R4 (e.g., CH3C(=O)H)
3. Compound C: R5C(=O)R6 (e.g., CH2=CHC(=O)H)
4. Compound D: R7C(=O)H (e.g., H2C=O)

3. **Identifying Electron-Donating and Electron-Withdrawing Effects**:
- Electron-donating groups (like alkyl groups) increase the electron density on the carbonyl carbon, making it less electrophilic and less reactive towards nucleophiles.
- Electron-withdrawing groups (like -CHO, -COOH) increase the positive character of the carbonyl carbon, making it more electrophilic and more reactive.

4. **Comparing the Compounds**:
- For each compound, we need to evaluate the presence of electron-donating or withdrawing groups:
- **Compound A**: Has two methyl groups (electron-donating), which reduce the electrophilicity.
- **Compound B**: Has one methyl group and a hydrogen (less electron-donating effect).
- **Compound C**: Has a vinyl group (alkene) which can have a moderate electron-withdrawing effect.
- **Compound D**: Has a carbonyl group with a hydrogen, which is highly electrophilic due to the absence of electron-donating groups.

5. **Determining the Most Reactive Compound**:
- Among the compounds analyzed, **Compound D** (R7C(=O)H) has the highest electrophilicity due to the absence of electron-donating groups. Therefore, it is the most reactive towards nucleophilic addition reactions.

### Conclusion:
The most reactive compound towards nucleophilic addition reactions is **Compound D**.

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