Question

With reference to the scheme given below, which of the following statement(s) is/are TRUE about the major products P, Q, R, S and T?

• A. Product P is optically active.
• B. Product Q is generated by an elimination that removes the original stereocentre.
• C. The conversion of Q to R with SOCl₂ proceeds by an SN2 process but since Q is achiral the “inversion” is moot.
• D. Product S (made by a free‐radical procedure) is racemic.
• E. Finally, the NBS/alc. KOH sequence gives T by an allylic bromination–elimination process.

Answer 1

Answer: (A), (B), (C), (D), (E)

The true statements are those that state: – P is optically active (pure enantiomer) – Q is formed by dehydration (thus “losing” the stereocentre) – S (and subsequently T) is formed through free‐radical processes (so that any new stereocenters are racemic)

Answer 2

1. LAH reduction of the lactone gives a diol (P) without disturbing the only chiral centre → P remains optically pure.

2. Dehydration with Al₂O₃ eliminates –OH (forming an alkene) thus removing the chiral centre → Q is achiral.

3. SOCl₂ converts the –OH (if any) via SN2 (inversion) but since the centre is now sp² the reaction does not “recover” chirality → R is not optically pure.

4. The radical bromination using HBr/peroxide (step 4) and NBS/hν (step 5) generate radicals so that the new stereocentres are racemic (in S or T).