Which one of the following is most reactive towards electrophilic reagent ?

Options

A.
B.
C.
D.

Explanation

To determine which compound is most reactive towards electrophilic reagents, 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 Compounds
Assume we have four aromatic compounds with different substituents in the ortho position relative to a methyl group. The substituents could be -OH, -OCH3, -NH2, and -SH.

### Step 2: Understand Electrophilic Aromatic Substitution
Electrophilic aromatic substitution (EAS) is a reaction where an electrophile replaces a hydrogen atom on an aromatic ring. The reactivity of the aromatic compound towards electrophiles is influenced by the nature of the substituents attached to the ring.

### Step 3: Analyze the Effects of Substituents
1. **-OH (Hydroxyl Group)**: This group has a strong +M (mesomeric) effect due to the presence of lone pairs on oxygen, which can donate electron density to the aromatic ring, increasing reactivity.
2. **-OCH3 (Methoxy Group)**: Similar to -OH, this group also exhibits a +M effect but is slightly less strong than -OH.
3. **-NH2 (Amino Group)**: This group also has a +M effect due to the lone pairs on nitrogen, contributing to increased reactivity.
4. **-SH (Thiol Group)**: This group has a weaker +M effect compared to the others.

### Step 4: Compare the +M Effects
- The order of +M effect strength is:
1. -OH (strongest)
2. -OCH3
3. -NH2
4. -SH (weakest)

### Step 5: Determine the Most Reactive Compound
Since the -OH group has the strongest +M effect, it will increase the electron density on the aromatic ring the most, making it the most reactive towards electrophilic reagents.

### Conclusion
The compound with the -OH substituent is the most reactive towards electrophilic reagents.

### Final Answer
The answer is the compound with the -OH group.

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