Which of the following is most reactive towards electrophillic aromatic substitution for halogen ?

Options

A.
B.
C.
D.

Answer

To determine which compound is most reactive towards electrophilic aromatic substitution for halogen, we need to analyze the substituents on the aromatic ring and their effects on reactivity. Here’s a step-by-step solution:

### Step 1: Identify the Substituents
List the substituents present on the aromatic compounds in the options provided. Common substituents include alkyl groups (like CH3), halogens (like Cl), and electron-withdrawing groups (like NO2).

### Step 2: Determine the Nature of Each Substituent
Evaluate whether each substituent is an electron-donating group (EDG) or an electron-withdrawing group (EWG):
- **Electron-Donating Groups (EDGs)**: These groups increase the electron density on the aromatic ring, making it more reactive towards electrophiles. Examples include alkyl groups (like CH3) and groups that exhibit resonance donation.
- **Electron-Withdrawing Groups (EWGs)**: These groups decrease the electron density on the aromatic ring, making it less reactive towards electrophiles. Examples include nitro groups (NO2) and halogens (like Cl).

### Step 3: Analyze the Effects of Each Substituent
- **CH3 Group**: This is an EDG due to hyperconjugation and inductive effects, increasing the reactivity of the aromatic ring.
- **NO2 Group**: This is a strong EWG, significantly decreasing the reactivity of the aromatic ring.
- **C2F5 Group**: This group has an alkyl component, which can act as an EDG, but the presence of fluorine atoms can also introduce some electron-withdrawing character.
- **Cl Group**: This is an EWG due to its -I (inductive) effect, although it can have some resonance donation.

### Step 4: Compare the Reactivity
Among the groups:
- The CH3 group is the strongest EDG and will make the aromatic ring highly reactive towards electrophilic substitution.
- The C2F5 group has some EDG characteristics but is less effective than CH3 due to the presence of electronegative fluorine atoms.
- The NO2 and Cl groups are both EWGs, which will decrease reactivity.

### Conclusion
The compound with the CH3 group is the most reactive towards electrophilic aromatic substitution for halogen due to its strong electron-donating effect.

**Final Answer**: The compound with the CH3 group (alkyl group) is the most reactive towards electrophilic aromatic substitution for halogen.

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