Reaction Sequence Problem
Q.25 The structure of Y in the above reaction sequence is:
Structure of Y in Reaction Sequence – Electrophilic Substitution of Anisole Explained
In organic chemistry reaction sequence problems, identifying the structure of an intermediate (Y)
requires understanding electrophilic aromatic substitution (EAS), directing effects of substituents,
and oxidation reactions. The methoxy group (–OCH3) strongly activates the benzene ring and
directs incoming groups to ortho and para positions. Let’s solve this step-by-step.
Step 1: Nature of Methoxy Group (–OCH3)
- Electron donating (+M effect)
- Strongly activating
- Ortho/Para directing
Therefore, during electrophilic substitution such as bromination, substitution mainly occurs at
ortho and para positions. Para is the major product due to less steric hindrance.
Step 2: Reaction Logic
Since bromination is an electrophilic substitution reaction, the bromine atom will attach directly to
the aromatic ring. Hence, the intermediate Y must be the brominated anisole product rather than an oxidized acid.
Option-wise Explanation
Option (A)
Methoxy + COOH substituted product
- Represents oxidation product
- Not first step intermediate
Rejected ❌
Option (B)
Side chain bromination
- Not aromatic substitution
- Mechanistically unlikely
Rejected ❌
Option (C)
Meta substituted product
- Methoxy directs ortho/para only
- Meta substitution incorrect
Rejected ❌
Option (D)
p-Bromoanisole (Br para to OCH3)
- Matches ortho/para directing rule
- Para product is major
- Correct electrophilic substitution intermediate
Correct Answer ✅
Final Answer
Option (D) – p-Bromoanisole
Key Concept Summary
| Concept | Explanation |
|---|---|
| Methoxy effect | Electron donating (+M) |
| Orientation | Ortho/Para directing |
| Major product | Para substituted |
| Structure of Y | p-Bromoanisole |
Exam Tips
- –OCH3 always gives ortho/para substitution
- Para product generally major
- Check directing effects before choosing answer
- Oxidation usually occurs after substitution
