Which of the following species can be isolated as a pair of configurationally stable enantiomers at room temperature? (Pyramidal inversion at nitrogen in a neutral amine is fast; inversion at sulfur and phosphorus is slow.)

A $N$ -Ethyl- $N$ -methylaniline, $C X_{6} H X_{5} - N (CH X_{3}) (CH X_{2} CH X_{3})$
BEthyl methyl sulfoxide, $CH X_{3} - S (= O) - CH X_{2} CH X_{3}$
CEthyl(methyl)phenylphosphine, $C X_{6} H X_{5} - P (CH X_{3}) (CH X_{2} CH X_{3})$
DEthyl methyl sulfone, $CH X_{3} - SO X_{2} - CH X_{2} CH X_{3}$

Answer: B, C

A stereogenic pyramidal centre needs four different 'groups' (a lone pair counts) and a high inversion barrier. The sulfoxide sulfur has

O

CH X_{3}

C X_{2} H X_{5}

and a lone pair, and the phosphine phosphorus has

C X_{6} H X_{5}

CH X_{3}

C X_{2} H X_{5}

and a lone pair; both invert slowly. The sulfone has two identical oxygens, and the neutral amine nitrogen inverts rapidly, so its enantiomers interconvert. Correct: A and C.

Practice Stereoisomerism More on Chirality, enantiomers and R/S configuration

Previous questionNext question

Which of the following species can be isolated as a pair of configurationally stable enantiomers at room temperature? (Pyramidal inversion at nitrogen in a neutral amine is fast; inversion at sulfur and phosphorus is slow.)

Answer: B, C

More questions on Chirality, enantiomers and R/S configuration