Discussion
The correct absolute configuration for the chiral centers in the following compound is :
![A bicyclo[2.2.1]heptan-2-one drawn in perspective, with a gem-dimethyl bridge carbon at the top, carbon 1 bearing H next to the C=O and carbon 4 bearing a methyl group](/uploads/question-images/sppu-mhset-2018-01-28-chemical-sciences-paper-2/q27.png)
Answer: C
Both chiral centres are R: 1R, 4R.
The compound is a trimethylbicyclo[2.2.1]heptan-2-one in which C1 carries H and is bonded to the carbonyl carbon, and C4 carries a methyl group. Because the bridgeheads are tied together by the bicyclic frame, the two centres are fixed relative to each other.
At C1 the priorities are C=O carbon (O,O,C) > C7, the gem-dimethyl bridge (C,C,C) > ring CH2 (C,H,H) > H. At C4 they are C7 (C,C,C) > the CH2 next to the carbonyl (it leads to O) > the other ring CH2 > CH3. Reading the perspective drawing with H at C1 and CH3 at C4 pointing away, the sequence 1 → 2 → 3 runs clockwise at each centre, so both are R.
In the bridged ring the two centres cannot be inverted independently, so a mixed pair such as 1S,4R or 1R,4S does not exist for this constitution, and 1S,4S is the mirror image of the compound drawn.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development