JEE Advanced 2025 Paper 2 Q08 Chemistry Organic Reactions & Mechanisms Aldehydes & Ketones Hard

JEE Advanced 2025 Paper 2 · Q08 · Aldehydes & Ketones

For the reaction sequence given below, the correct statement(s) is(are):

Phenyl glycidate ($Ph$-epoxide-$CH$-$COOR$ -- an epoxy ester of styrene oxide) -> $LiAlH_4$ -> P (a 1,2-diol $Ph-CH(OH)-CH(OH)-...$ or $Ph-CH(OH)-CH_2-OH$ after epoxide opening + ester reduction). P -> $CrO_3-H_2SO_4$ (Jones) -> Q (a carboxylic acid). Q -> $NaOH$ and $CaO$, heat -> R. P -> $H_2SO_4$, 443 K -> S (dehydration product, an alkene).

  1. A. P is optically active.
  2. B. S gives Bayer's test.
  3. C. Q gives effervescence with aq. $NaHCO_3$.
  4. D. R is an alkyne.
JEE Advanced multi-correct — pick every correct option, then check.
Reveal answer + step-by-step solution

Correct answer:B, C

Solution

$LiAlH_4$ reduction of the epoxy-ester opens the epoxide and reduces the ester to give the racemic diol P. (A) Racemic mixtures are NOT optically active overall. FALSE. Q is a carboxylic acid (Jones oxidation of the primary alcohol). Carboxylic acid + aq. $NaHCO_3$ -> evolves $CO_2$ (effervescence). (C) TRUE. S is the dehydration product of the diol (alkene/styrene-type). Alkenes give Baeyer's test (decolourise cold dilute alkaline $KMnO_4$). (B) TRUE. R is the decarboxylation product of Q under $NaOH/CaO$ (soda-lime decarboxylation), giving an arene/alkylbenzene, NOT an alkyne. (D) FALSE. Correct: (B), (C).

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