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Question #44039
The Question
Consider the enantiomerically pure compound \ce{X}, (2S)-2-(4-nitrophenyl)propanamide. \ce{X} is subjected to two distinct reaction sequences:
Sequence 1: \ce{X} is treated with \ce{Br2} (1 eq.) and aqueous \ce{NaOH} at . The resulting intermediate is then reacted with \ce{SnCl2 / HCl} followed by neutralization with excess \ce{NaOH} to yield the major product \ce{P}.
Sequence 2: \ce{X} is treated with \ce{B2H6} in THF, followed by acidic workup and subsequent neutralization to yield the major product \ce{Q}.
Identify the correct IUPAC names and stereochemical descriptors for products \ce{P} and \ce{Q}.
Options
- A.
\ce{P}: (1S)-1-(4-aminophenyl)ethan-1-amine, \ce{Q}: (2S)-2-(4-nitrophenyl)propan-1-amine
- B.
\ce{P}: (1S)-1-(4-aminophenyl)ethan-1-amine, \ce{Q}: (2R)-2-(4-nitrophenyl)propan-1-amine
- C.
\ce{P}: (1R)-1-(4-aminophenyl)ethan-1-amine, \ce{Q}: (2S)-2-(4-aminophenyl)propan-1-amine
- D.
\ce{P}: (2S)-2-(4-aminophenyl)propan-1-amine, \ce{Q}: (1S)-1-(4-nitrophenyl)ethan-1-amine
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Exception_Exposure
Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.
Concepts Behind This Question
Hoffmann Bromamide Rearrangement|Reduction Selectivity (Sn/HCl vs LiAlH4)|Inductive Effect Trends
Why This Question Is Tricky
Common Mistakes
The problem tests chemoselectivity and stereochemical fidelity.
A major trap is the CIP priority assignment in product Q.
Students often erroneously assign higher priority to the massive nitrophenyl group over the smaller aminomethyl group, leading to an incorrect (R) designation.
Furthermore, students frequently over-apply generic reduction logic, assuming B2H6 reduces nitro groups (it does not) or forgetting that HBR degrades the carbon chain by one carbon while strictly retaining stereochemistry.
The inductive effect (-I) of the nitro group slows the HBR migration but does not alter the chemoselective or stereochemical outcome.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Amines - Class 12 |
| Concept | Hoffmann Bromamide Rearrangement |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |