See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Hydration of alkynes with HgSO4/dil. H2SO4 (Markovnikov addition of water) converts alkynes to carbonyl compounds (ketones or aldehydes). Reduction of a ketone with LiAlH4 produces a secondary alcohol, which can be chiral and thus form a racemic mixture. Step 1: The final product (C) is a racemic mixture, meaning it contains a chiral center. A racemic mixture is formed when a prochiral carbonyl compound (specifically a ketone with two different alkyl groups) is reduced by LiAlH4, which attacks from both faces of the carbonyl equally, producing equal amounts of R and S enantiomers. Step 2: For (B) to give a racemic mixture upon LiAlH4 reduction, (B) must be a ketone with two different groups on either side of the carbonyl — i.e., an unsymmetrical ketone. Reduction of an aldehyde gives a primary alcohol (only one 'H' and one alkyl group on the carbon — actually it does give a chiral center if the resulting alcohol is chiral, but let's check each option). Step 3: Evaluate each option for hydration product (B): - (a) CH3-C≡CH (propyne): Markovnikov hydration gives CH3-CO-CH3 (acetone) — a symmetrical ketone, reduction gives 2-propanol which has no chiral center → NO racemic mixture. - (b) HC≡CH (acetylene): hydration gives CH3CHO (acetaldehyde) — an aldehyde, reduction gives ethanol — no chiral center → NO racemic mixture. - (c) CH3-C≡C-CH3 (2-butyne): Markovnikov hydration gives CH3-CO-CH2-CH3... wait, actually for an internal symmetric alkyne, hydration gives CH3-CO-CH2-CH3? No — 2-butyne is symmetric, so hydration gives CH3-C(=O)-CH2CH3? Actually 2-butyne hydration gives butanone (CH3COCH2CH3) — an unsymmetrical ketone. LiAlH4 reduction of butanone gives 2-butanol (CH3-CH(OH)-CH2CH3), which has a chiral center at C2. Since LiAlH4 is achiral and attacks both faces, it gives a racemic mixture of (R)- and (S)-2-butanol. This matches the condition. - (d) Ph-CH=CH2 (styrene): this is an alkene, not an alkyne, and HgSO4/dil. H2SO4 is used for alkyne hydration. Even if it reacted, it would give PhCH(OH)CH3 directly or PhCOCH3 — but styrene is not an alkyne. Step 4: Why not option (a)? Propyne gives acetone (symmetric ketone) → 2-propanol has no chiral center, no racemic mixture possible. Why not option (b)? Acetylene gives acetaldehyde → ethanol, no chirality. Why not option (d)? Styrene is an alkene, not an alkyne; HgSO4/dil. H2SO4 is specific for alkynes. Step 5: Option (c) CH3-C≡C-CH3 (2-butyne) → hydration gives butanone (methyl ethyl ketone) → LiAlH4 reduction gives racemic 2-butanol. This perfectly matches all the given conditions. Therefore, the correct answer is C.