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GATE 2026 CY – Question 23

Organic Chemistry · Stereochemistry: Chirality and symmetry of organic molecules with or without chiral centres and determination of their absolute configurations and optical purity. Relative stereochemistry in compounds having more than one stereogenic centre. Homotopic, enantiotopic and diastereotopic atoms, groups and faces. Conformational analysis of acyclic and cyclic compounds. Geometrical isomerism and optical isomerism. Configurational and conformational effects, atropisomerism, and neighbouring group participation on reactivity and selectivity/specificity. Stereoselective and stereospecific synthesis. Enantiomeric excess. · 1 mark · Multiple select

In the 1H NMR spectrum of compound X, the coupling constant (Jab) between Ha and Hb is 3 Hz. The amino alcohol(s) that give(s) X on reaction with methyl iodide followed by heating is(are)

Diphenylisochroman X with Ha/Hb labels and four stereochemical amino-alcohol precursors.
  1. Option A in the figure
  2. Option B in the figure
  3. Option C in the figure
  4. Option D in the figure

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Show answer and explanation

Correct answer: (B) Option B in the figure; (C) Option C in the figure

Explanation

B and C are the accepted amino-alcohol precursors. Use the small 3 Hz vicinal coupling to identify the product conformation, then track the stereochemical change during displacement after quaternization with methyl iodide. Assuming that the substitution leaves both reacting configurations unchanged led to the wrong A,D pair.

Official GATE 2026 answer key: https://gate2026.iitg.ac.in/doc/download/2026/Keys/CY_Keys.pdf