Choose the most reactive among the following compound :

Options

A.
B.
C.
D.

Answer

To determine the most reactive compound among the given alkyl derivatives of benzene, we will analyze the compounds based on their ability to donate electron density to the benzene ring, which is crucial for electrophilic substitution reactions.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We have four alkyl derivatives of benzene. Let's denote them as:
- Compound A: Toluene (methylbenzene)
- Compound B: Ethylbenzene
- Compound C: Propylbenzene
- Compound D: Benzene (for comparison)

2. **Understand the Reactivity in Electrophilic Substitution**:
- Benzene is an electron-rich species and undergoes electrophilic substitution reactions.
- The reactivity of benzene derivatives is influenced by substituents that can either donate or withdraw electron density.

3. **Identify Electron Donating and Withdrawing Groups**:
- Alkyl groups (like methyl, ethyl, propyl) are electron-donating groups due to their +I (inductive) effect.
- The more electron density that can be provided to the benzene ring, the more reactive the compound will be.

4. **Consider Hyperconjugation**:
- Hyperconjugation occurs when alkyl groups donate electron density through the overlap of σ-bonds with the empty p-orbitals of the benzene ring.
- The extent of hyperconjugation depends on the number of alpha hydrogens attached to the alkyl group.

5. **Count the Alpha Hydrogens**:
- **Toluene (Compound A)**: Has 3 alpha hydrogens (from the methyl group).
- **Ethylbenzene (Compound B)**: Has 5 alpha hydrogens (from the ethyl group).
- **Propylbenzene (Compound C)**: Has 7 alpha hydrogens (from the propyl group).
- **Benzene (Compound D)**: Has no substituent, hence no alpha hydrogens.

6. **Determine the Most Reactive Compound**:
- The compound with the highest number of alpha hydrogens will exhibit the most hyperconjugation and thus increase the electron density on the benzene ring the most.
- Comparing the alpha hydrogens:
- Toluene: 3
- Ethylbenzene: 5
- Propylbenzene: 7
- Benzene: 0
- Propylbenzene has the most alpha hydrogens (7), making it the most reactive compound among the options.

7. **Conclusion**:
- The most reactive compound among the given options is **Propylbenzene**.

### Final Answer:
The most reactive compound among the given options is **Propylbenzene**.