Which one the following has maximum reactivity towards HCN ?

Options

A. HCHO
B. `CH_3COCH_3`
C. `CH_3CHO`
D. `C_2H_5COCH_3`

Answer

To determine which compound has the maximum reactivity towards HCN, we need to analyze the electron-withdrawing or electron-donating effects of the substituents on the carbonyl carbon of the compounds provided. The more electron-deficient the carbonyl carbon is, the more reactive it will be towards nucleophiles like HCN.

### Step-by-Step Solution:

1. **Identify the Compounds**: Let's analyze the given options:
- Option 1: HCHO (Formaldehyde)
- Option 2: CH3COCH3 (Acetone)
- Option 3: CH3CHO (Acetaldehyde)
- Option 4: C2H5COCH3 (Butyrophenone)

2. **Understand the Reactivity of Carbonyl Compounds**: In carbonyl compounds, the carbon atom is electrophilic due to the partial positive charge created by the electronegative oxygen atom. Nucleophiles like HCN will attack this electrophilic carbon.

3. **Evaluate the Electron-Withdrawing and Electron-Donating Effects**:
- **Formaldehyde (HCHO)**: The hydrogen atom does not donate electron density, making the carbonyl carbon more positive and thus more reactive.
- **Acetone (CH3COCH3)**: The two methyl groups are electron-donating, which reduces the positive charge on the carbonyl carbon, making it less reactive than formaldehyde.
- **Acetaldehyde (CH3CHO)**: The methyl group donates some electron density, but less than acetone, so it is more reactive than acetone but less than formaldehyde.
- **Butyrophenone (C2H5COCH3)**: Both the ethyl and methyl groups donate electron density, further reducing the positive charge on the carbonyl carbon, making it the least reactive.

4. **Rank the Reactivity**:
- HCHO (most reactive)
- CH3CHO (more reactive than acetone)
- CH3COCH3 (less reactive)
- C2H5COCH3 (least reactive)

5. **Conclusion**: Based on the analysis, the compound with the maximum reactivity towards HCN is **HCHO (Formaldehyde)**.

### Final Answer:
**HCHO (Formaldehyde)** has the maximum reactivity towards HCN.