The configurations at the two asymmetric centres (C-1 and C-6) in the bicyclo [4.4.0] decane, given below are · ABC26OR0746
Subject: Organic Chemistry · Chapter: Stereochemistry · Topic: Stereochemistry – General · Exam: GATE 2000-2022 · Marks: 2 · Difficulty: Hard
The configurations at the two asymmetric centres (C-1 and C-6) in the bicyclo [4.4.0] decane, given below are 
(a)1R, 6R
(b)1R, 6S
(c)1S, 6S
(d)1S, 6R
Answer
Answer (as printed): B
Explanation
Bicyclo[4.4.0]decane numbering: C-1 is the ring-fusion carbon bearing Me, C-2 is the C=O, and C-6 is the other ring-fusion carbon (H dashed).
C-1 (Me on a wedge, toward the viewer): priorities C-2 (O,O,C) > C-6 (C,C,H) > C-10 (C,H,H) > CH₃. In the drawing C-2 → C-6 → C-10 runs anticlockwise; the lowest group points toward the viewer, so the sense is reversed and C-1 is R.
C-6 (H dashed, away): priorities C-1 (C,C,C) > C-5 (its path reaches the C=O carbon first) > C-7 > H. C-1 → C-5 → C-7 runs anticlockwise, so C-6 is S.
Configuration: 1R, 6S, option (b).
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