In the reaction H-C CH [(2)\ CH_3CH_2Br](1)\ NaNH_2/liq.NH_3 X [(2)\ CH_3CH_2Br](1)\ NaNH_2/liq.NH_3 Y, X and Y are :

1. X = 1-Butyne ; Y = 3-Hexyne

2. X = 2-Butyne ; Y = 3-Hexyne

3. X = 2-Butyne ; Y = 2-Hexyne

4. X = 1-Butyne ; Y = 2-Hexyne

Doubtly Asked 30 Oct 2026 NEET UG 2016 Phase 1 Practice test neet Save WhatsApp Report

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Answer: 1. X = 1-Butyne ; Y = 3-Hexyne

Key idea: the terminal alkyne H is acidic, so \(\mathrm{NaNH_2}\) removes it and the acetylide ion attacks the alkyl halide (\(\mathrm{S_N2}\)).

\(\mathrm{HC\equiv CH}\to \mathrm{HC\equiv C^-Na^+}\xrightarrow{\mathrm{CH_3CH_2Br}}\mathrm{HC\equiv C-CH_2CH_3}\) (X = 1-butyne).
X still has a terminal H. Repeat: \(\mathrm{CH_3CH_2C\equiv C^-}\) + \(\mathrm{CH_3CH_2Br}\) gives \(\mathrm{CH_3CH_2C\equiv CCH_2CH_3}\) (Y = 3-hexyne).

2-Butyne and 2-hexyne are not formed because the alkyl group is added at the carbon that lost the H, and both added groups are ethyl.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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