JEE Main 2022 · 29 July · evening · Single correct · +4 / −1
Compound 'A' undergoes following sequence of reactions to give compound 'B'.
The correct structure and chirality of compound 'B' is
[where Et is -C₂ H₅]
- (a)
- (b)
- (c)
- (d)
Answer and solution
Answer (c)
Solution
Chemistry ma’am · 4 steps
Mg then D₂O swaps Br for D, and that one D is enough to make C-2 a stereocentre.
- Identify A. Compound A is 2-bromo-3-methylbutane, (CH₃)₂CH-CHBr-CH₃. The Br sits on C-2.
- Grignard, then D2O. Mg in dry ether inserts between C and Br to give (CH₃)₂CH-CH(MgBr)-CH₃. This carbanion-like carbon is a strong base, so it pulls a deuteron off D₂O. Br is replaced by D on the same carbon, and no oxygen ends up on carbon.
(CH₃)₂CH-CHBr-CH₃ →(Mg, Et₂O) (CH₃)₂CH-CH(MgBr)-CH₃ →(D₂O) (CH₃)₂CH-CHD-CH₃
- Check C-2. C-2 now carries four groups: H, D, CH₃ and CH(CH₃)₂. H and D are different isotopes, so all four groups are different and C-2 is a chiral centre.
- So. B is 2-deuterio-3-methylbutane (D written as ²H), and it is chiral. That is option (c).
The idea to keep. A Grignard quenched with D₂O puts D exactly where the halogen was. When you hunt for a chiral centre, treat H and D as different groups.
Answer from the NTA final answer key. Solution by PrepWiser.