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NEET CHEMISTRYHydrocarbonsMedium

Question

X and Y in the above-mentioned reaction are respectively:

A

X = 2–Butyne; Y = 3–Hexyne

B

X = 2-Butyne; Y = 2-Hexyne

C

X = 1-Butyne; Y = 2-Hexyne

D

X = 1-Butyne; Y = 3–Hexyne

Step-by-Step Solution

  1. Missing Data Analysis: The specific reaction scheme is not provided in the text, but the question asks to identify reactants/products X and Y. Based on the options and standard alkyne chemistry, the reaction likely involves the conversion of a lower alkyne (X) to a higher alkyne (Y).
  2. Chemical Principle (Acidity of Alkynes): Terminal alkynes (like 1-Butyne) possess an acidic hydrogen atom attached to the spsp hybridised carbon atom. They react with strong bases like sodamide (NaNH2NaNH_2) to form stable sodium alkynides [NCERT 11th, Hydrocarbons, Sec 13.4.4; Source 136, 303]. R−C≡C−H+NaNH2→R−C≡C−Na++NH3R-C \equiv C-H + NaNH_2 \rightarrow R-C \equiv C^- Na^+ + NH_3 Internal alkynes (like 2-Butyne) do not have this acidic hydrogen and do not undergo this reaction.
  3. Synthesis of Higher Alkynes: The sodium alkynide formed can react with primary alkyl halides (e.g., Ethyl bromide, C2H5BrC_2H_5Br) via nucleophilic substitution to form higher alkynes. CH3CH2−C≡C−Na++C2H5Br→CH3CH2−C≡C−CH2CH3+NaBrCH_3CH_2-C \equiv C^- Na^+ + C_2H_5Br \rightarrow CH_3CH_2-C \equiv C-CH_2CH_3 + NaBr
  4. Deduction:
  • For X to react, it must be a terminal alkyne. This suggests X is 1-Butyne (CH3CH2−C≡CHCH_3CH_2-C \equiv CH), eliminating 2-Butyne options.
  • If 1-Butyne is alkylated with an ethyl group (to increase carbon count from C4 to C6), the product is 3-Hexyne (CH3CH2−C≡C−CH2CH3CH_3CH_2-C \equiv C-CH_2CH_3).
  • Option 4 matches this sequence.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Hydrocarbons. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYHydrocarbonsabovementionedreactionrespectively

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