Q9 · CSIR-NET Chemistry, June 2011
Paper: CSIR-NET June 2011 · Subject: Organic Chemistry · Chapter: General Organic Chemistry · Topic: General Organic Chemistry – General · Marks: 2 · Difficulty: Medium
The configurations at the two stereocentres in the compound given below are 
(a)1R, 4R
(b)1R, 4S
(c)1S, 4R
(d)1S, 4S
Answer
Answer (as printed): A
Explanation
Number the bicyclo[2.2.2]octenone as in the figure: C-1 carries Me (hashed, pointing away), C-2 is the C=O carbon, C-5=C-6 the alkene and C-7/C-8 the CH₂CH₂ bridge; C-4 carries H (wedge, toward the viewer).
C-1: C-2 (O,O,C) > C-6 (=CH: C,C,H) > C-7 (CH₂: C,H,H) > CH₃. With Me pointing away, C-2 → C-6 → C-7 runs clockwise: 1R.
C-4: C-5 (=CH: C,C,H) > C-3 (CH₂, leads to C=O) > C-8 (CH₂, leads to CH₂) > H. The sequence C-5 → C-3 → C-8 is anticlockwise as drawn, but H points toward the viewer, so the descriptor reverses: 4R.
Answer: 1R, 4R (a).
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