The alkyne shown is treated with Na in liquid NH3, then with m-CPBA, and finally with aqueous H3O+ (anti opening of the epoxide). What is the outcome?

A racemic mixture of (2R,3R)- and (2S,3S)-butane-2,3-diol

Only the (2R,3R)-diol, optically pure

MolSynapse / Question bank / Reduction, Oxidation and Hydrolysis in Organic Chemistry / Birch and Na/NH3 vs Lindlar on drawn substrates

JEE Advanced levelSingle correct optionDifficulty 3 of 3ro244

The alkyne shown is treated with Na in liquid $NH X_{3}$ , then with m-CPBA, and finally with aqueous $H X_{3} O X^{+}$ (anti opening of the epoxide). What is the outcome?

AThe meso diol, butane-2,3-diol
BA racemic mixture of (2R,3R)- and (2S,3S)-butane-2,3-diol
COnly the (2R,3R)-diol, optically pure
DUnchanged 2,3-dimethyloxirane

Answer: A

The compound is but-2-yne. Na/

NH X_{3}

gives (E)-but-2-ene, m-CPBA converts it stereospecifically into trans-2,3-dimethyloxirane (a chiral racemate), and anti ring opening by water at either carbon gives the meso diol. Net anti addition of two OH to an E alkene gives the meso compound, whereas the Z alkene would give the racemate.

Practice Reduction, Oxidation and Hydrolysis in Organic Chemistry More on Birch and Na/NH3 vs Lindlar on drawn substrates

Previous questionNext question

The alkyne shown is treated with Na in liquid NHX3​, then with m-CPBA, and finally with aqueous HX3​OX+ (anti opening of the epoxide). What is the outcome?

Answer: A

More questions on Birch and Na/NH3 vs Lindlar on drawn substrates

The alkyne shown is treated with Na in liquid $NH X_{3}$ , then with m-CPBA, and finally with aqueous $H X_{3} O X^{+}$ (anti opening of the epoxide). What is the outcome?