Treatment of buta-1,3-diyne with NaNH2 (2 equivalents), followed by reaction with excess of trans- CH3−CH=CH−CH2−Br gives X as the major product. The maximum number of carbon atoms that are collinear (in a straight line) in X is ____.
Answer: 6
Solution
Buta-1,3-diyne (HC≡C-C≡CH) is treated with 2 equivalents of NaNH2, which deprotonates both terminal alkynes to form the dianion.
This dianion then reacts with excess trans-CH3CH=CHCH2Br via SN2 substitution at both ends.
The product X has the structure where the central C≡C-C≡C unit (4 carbons) remains linear, and each end is connected to an allyl group.
The maximum number of collinear carbon atoms includes the four carbons of the diyne unit plus one carbon from each of the two allyl groups that align with the triple bonds.
Maximum collinear carbons = 6
JEE Advanced · 2026 · 17 May 2026 · Paper 1 · Numerical answer
