Absolute stereochemistry of the given compound is: · ABC26OR0701
Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Reagents, Reaction Mechanisms & Named Reactions – General · Exam: GATE 2000-2022 · Marks: 2 · Difficulty: Easy
Absolute stereochemistry of the given compound is: 
(a)$4a\mathrm{S}, 8a\mathrm{R}$
(b)$4a\mathrm{R}, 8a\mathrm{S}$
(c)$4a\mathrm{S}, 8a\mathrm{S}$
(d)$4a\mathrm{R}, 8a\mathrm{R}$
Answer
Answer: A ✓ checked by 4AB · confidence high
The source book printed no answer; this one was worked out and checked — see the explanation.
There was no answer key. CIP analysis of the drawn structure: C8a (C1 ketone > CHO > C4a > C8, CHO hashed) is R; C4a (OH > C8a > C4 > C5, OH hashed) is S. That gives 4aS, 8aR = (a).
Explanation
C8a: the priorities are C1 (ketone carbon; O, O, C) > CHO (O, O, H) > C4a (O, C, C) > C8 (C, H, H). The CHO group is hashed (pointing back) and the lowest-priority C8 lies in the plane. Tracing 1 → 2 → 3 gives R, so C8a is R.
C4a: the priorities are OH > C8a (C, C, C) > C4 (next to the alkene carbon C3) > C5. The OH is hashed (pointing back), and the 1 → 2 → 3 sequence gives S, so C4a is S. Answer: (a) 4aS, 8aR.
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