Question

Which of the following statements about the stereochemical outcomes of substitution reactions are TRUE? (check all that are true)

The carbocation intermediate in S_N1 reactions can be attacked from either side giving a mixture of stereoisomers.

S_N2 reactions give complete retention of configuration.

S_N2 reactions give only inversion of stereochemistry

S_N1 reactions give racemic products or mixtures of diastereomers.

Answer 1

The true statements about stereochemical outcomes of substitution reactions are

The carbocation intermediate in S_N1 reactions can be attacked from either side giving a mixture of stereoisomers.

Explanation:

S_N1 reactions undergoes in two step where 1st step is formation of carbocation from alkyl halide. Alkyl halide carbon have SP3 hybridization which makes the structure of tetrahedral geometry but its carbocation have SP2 hybridized carbon where its orbitals stays in single plane in triagonal fashion. If a structure have this kind of geometry then it have two side opposite to each other open for attack. So thats why nucleophile can attack from both side.

S_N2 reactions give only inversion of stereochemistry

Explanation:

S_N2 reactions undergoes in single step where an intermediate of transtition step forms. At this step nucleophile attack the carbon without cleaving the leaving group. So it attacks from the opposite side of the leaving group and form an umbrella like geometry of the molecule and this phase is called walden inversion.

S_N1 reactions give racemic products or mixtures of diastereomers .

Explanation:

S_N1 reactions produces mixture of stereoisomer we already discussed so it can give racemic mixture. But if starting material does have more than 1 chiral center then it can produces diastereomers also.