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JEE Advanced levelSingle correct optionDifficulty 3 of 3o3093

$(2 R, 5 R)$ -5-Chlorohexan-2-ol is treated with a dilute aqueous solution of $NaOH$ and the only reaction is intramolecular SN2 (the alkoxide displaces chloride at C5; the C2-O bond is not broken). The product is

A $(2 S, 5 S)$ -2,5-dimethyloxolane, a trans isomer
B $(2 R, 5 R)$ -2,5-dimethyloxolane, a trans isomer
Ca racemic mixture of the trans isomers $(2 R, 5 R)$ and $(2 S, 5 S)$
D $(2 R, 5 S)$ -2,5-dimethyloxolane, the achiral cis (meso) isomer

Answer: D

The alkoxide at C2 closes a five-membered ring by backside attack on C5, which inverts C5 only. At C5 the priorities are

Cl > C X_{4} > CH X_{3} > H

in the substrate and

O > C X_{4} > CH X_{3} > H

in the ring, so the label changes from

R

to

S

. C2 is not touched and stays

R

. The product

(2 R, 5 S)

is the meso, cis-2,5-dimethyloxolane.

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