The major product M formed in the following reaction is · ABC26OR0620
Subject: Organic Chemistry · Chapter: Reagents, Reaction Mechanisms & Named Reactions · Topic: Reagents, Reaction Mechanisms & Named Reactions – General · Exam: GATE 2000-2022 · Marks: 2 · Difficulty: Easy
The major product M formed in the following reaction is 
(a)
(b)
(c)
(d)
Answer
Answer: B ✓ checked by 4AB · confidence high
The source book printed no answer; this one was worked out and checked — see the explanation.
The substrate on the scan is (1Z,5E)-cyclodeca-1,5-diene. Diimide reduces the strained E bond selectively, leaving (Z)-cyclodecene. Option (a) is drawn with the trans (E) alkene and (b) with the cis (Z) alkene, so the answer is (b), not (a).
Explanation
Diimide (HN=NH), generated from N₂H₄/Cu²⁺/O₂, adds H₂ by a concerted syn transfer, and its rate rises sharply with alkene strain. The substrate is (1Z,5E)-cyclodeca-1,5-diene. The trans C=C in a ten-membered ring is far more strained, so 1 equiv of N₂H₄ reduces it selectively and leaves the cis double bond: (Z)-cyclodecene. In the options, (a) keeps the trans-drawn alkene (E-cyclodecene) and (b) keeps the cis one. Answer: (b).
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