Which of the following compounds shall not produce propene by reaction with HBr followed by elimination or direct only elimination reaction?

Options

A. Cyclopropane
B. `H_3C-CH_2-CH_2OH`
C. `H_2C=C=O`
D. `H_3C-CH_2-CH_2Br`

Answer

To determine which compound does not produce propene by reaction with HBr followed by elimination or direct elimination, we will analyze each option step by step.

### Step 1: Analyze Cyclopropane (Option A)
- **Structure**: Cyclopropane is a three-membered ring with the formula C3H6.
- **Reaction with HBr**: When cyclopropane reacts with HBr in the presence of UV light, it undergoes radical cleavage, leading to the formation of radicals.
- **Formation of Propene**: The radicals can rearrange and eliminate hydrogen to form propene (C3H6).
- **Conclusion**: Cyclopropane can produce propene.

### Step 2: Analyze 1-Propanol (Option B)
- **Structure**: 1-Propanol has the formula CH3CH2CH2OH.
- **Reaction with HBr**: In the presence of H+, the hydroxyl group (OH) can be protonated to form a better leaving group (water).
- **Elimination Reaction**: The elimination of water leads to the formation of a carbocation, which can rearrange to form a more stable carbocation and subsequently eliminate a proton to form propene.
- **Conclusion**: 1-Propanol can produce propene.

### Step 3: Analyze Ketene (Option C)
- **Structure**: Ketene has the formula CH2=C=O.
- **Reactivity**: Ketene does not undergo reactions that lead to the formation of alkenes like propene. Instead, it reacts with nucleophiles or can form other products.
- **Conclusion**: Ketene does not produce propene.

### Step 4: Analyze 1-Bromopropane (Option D)
- **Structure**: 1-Bromopropane has the formula CH3CH2CH2Br.
- **Reaction with HBr**: In the presence of a strong base (like KOH), it can undergo elimination (dehydrohalogenation).
- **Formation of Propene**: The elimination of HBr leads to the formation of propene.
- **Conclusion**: 1-Bromopropane can produce propene.

### Final Conclusion:
The compound that does not produce propene by reaction with HBr followed by elimination or direct elimination is **Option C: Ketene**.

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