JEE Main 2022 · 25 July · morning · Single correct · +4 / −1
A compound ‘A’ on reaction with ‘X’ and ‘Y’ produces the same major product but different by product 'a' and 'b′. Oxidation of 'a' gives a substance produced by ants.
'X' and 'Y' respectively are
- (a) KMnO₄ / H⁺ and dil. KMnO_(4′) 273 K
- (b) KMnO₄ (dilute), 273 K and KMnO₄ / H⁺
- (c) KMnO₄ / H⁺ and O₃, H₂ O / Zn
- (d) O₃, H₂ O / Zn and KMnO₄ / H⁺
Answer and solution
Answer (d) O₃, H₂ O / Zn and KMnO₄ / H⁺
Solution
Chemistry ma’am · 4 steps
Look at the CH₂= end: the reagent that leaves it as HCHO is X, because HCHO oxidises to formic acid.
- Read compound A. A is CH₂=C(CH₃)-CH₂-C(CH₃)₃. Both reactions break the C=C bond and give the same ketone, CH₃COCH₂C(CH₃)₃, from the substituted carbon. So both X and Y must cleave the double bond. They differ only in what the terminal CH₂ becomes.
Reagent Effect on the double bond Ketone formed? Fate of the =CH₂ carbon O₃, then Zn/H₂O reductive cleavage yes stops at HCHO KMnO₄/H⁺ oxidative cleavage yes HCHO → HCOOH → CO₂ + H₂O dil. KMnO₄, 273 K adds two OH groups, no cleavage no, gives a diol stays as CH₂OH in the diol - Identify a. Ants produce formic acid, HCOOH. The only by-product that oxidises to it is formaldehyde, HCHO. So a is HCHO, and X is ozonolysis with Zn/H₂O.
- Identify b. Hot acidic KMnO₄ gives the same ketone, but it oxidises the CH₂ end all the way to CO₂ and water. So b is CO₂, and Y is KMnO₄/H⁺.
- So. X is O₃, H₂O/Zn and Y is KMnO₄/H⁺, which is option (d).
The idea to keep. A terminal =CH₂ gives HCHO on reductive ozonolysis but CO₂ with acidic KMnO₄. Cold dilute KMnO₄ never cleaves the double bond. It only makes a diol.
Answer from the NTA final answer key. Solution by PrepWiser.