Chapter 8, Problem 8.13P

Interpretation Introduction

(a)

Interpretation:

The complete, detailed mechanism and products for the given reaction are to be drawn assuming that it takes place via an ${\text{S}}_{\text{N}}2$ mechanism, paying attention to stereochemistry.

Concept introduction:

${\text{S}}_{\text{N}}2$ reaction is the bimolecular nucleophilic substitution reaction. The halide group in the substrate acts as a good leaving group. In an ${\text{S}}_{\text{N}}2$ reaction, the incoming nucleophile attacks the carbon that is bonded to the leaving group, with the leaving group breaking off simultaneously with its bond pair. The incoming group must attack the carbon from a direction opposite the leaving group. The result is generally a single product. As ${\text{S}}_{\text{N}}2$  reaction is a single-step reaction, the stereo-specificity suggests that the nucleophile attacks the substrate exclusively from the side opposite the leaving group, producing a single stereoisomer. Thus, ${\text{S}}_{\text{N}}2$  reactions are stereospecific.

Answer to Problem 8.13P

The complete, detailed mechanism for the given reaction, assuming that it takes place via an ${\text{S}}_{\text{N}}2$ mechanism, paying attention to stereochemistry, is

Explanation of Solution

The given reaction is:

The reactant molecule contains one chiral center at the C2 carbon atom. The leaving group is ${\text{Br}}^{-}$, and the nucleophile is ${\text{I}}^{-}$. In an ${\text{S}}_{\text{N}}2$ reaction, the ${\text{I}}^{-}$ nucleophile should attack from the side opposite the $\text{C-Br}$ bond, in this case, from the front side of the plane of the page. Thus, the new $\text{C-I}$ bond remains in the front side of the plane of the page attached by a wedge bond. Complete and detailed mechanism of the given reaction is as follows:

In given alkyl halide C2 carbon atom is chiral in nature and affected throughout the course of the reaction. The nucleophile ${\text{I}}^{\text{-}}$ attacks from the side opposite the $\text{C-Br}$ bond (in this case, in front of the plane of the page), and new $\text{C-I}$ bond is formed. The final product will have the configuration opposite to that of the reactant molecule, producing a single stereoisomer.

Conclusion

For the given ${\text{S}}_{\text{N}}2$ reaction, the complete and detailed mechanism and products are shown above.

Interpretation Introduction

(b)

Interpretation:

The complete, detailed mechanism and products for the given reaction are to be drawn assuming that it takes place via an ${\text{S}}_{\text{N}}2$ mechanism, paying attention to stereochemistry.

Concept introduction:

${\text{S}}_{\text{N}}2$ reaction is the bimolecular nucleophilic substitution reaction. The halide group in the substrate acts as a good leaving group. In an ${\text{S}}_{\text{N}}2$ reaction, the incoming nucleophile attacks the carbon that is bonded to the leaving group, with the leaving group breaking off simultaneously with its bond pair. The incoming group must attack the carbon from a direction opposite the leaving group. The result is generally a single product. As ${\text{S}}_{\text{N}}2$  reaction is a single-step reaction, the stereo-specificity suggests that the nucleophile attacks the substrate exclusively from the side opposite the leaving group, producing a single stereoisomer. Thus, ${\text{S}}_{\text{N}}2$  reactions are stereospecific.

Answer to Problem 8.13P

The complete, detailed mechanism for the given reaction, assuming that it takes place via an ${\text{S}}_{\text{N}}2$ mechanism, paying attention to stereochemistry, is

Explanation of Solution

The given reaction is

The reactant molecule contains two chiral centers at C1 and C3 carbon atoms. The leaving group is ${\text{OH}}_{\text{2}}{}^{\text{+}}$, and the nucleophile is ${\text{Br}}^{-}$. In an ${\text{S}}_{\text{N}}2$ reaction, the ${\text{Br}}^{-}$ nucleophile should attack from the side opposite the ${\text{C-OH}}_{\text{2}}{}^{\text{+}}$ bond, in this case, from behind the plane of the page. Thus, the new $\text{C-Br}$ bond remains behind the plane of the page attached by a dash bond. Complete and detailed mechanism of the given reaction is as follows:

Note that the stereochemical configuration at the chiral center at C3 remains unchanged because no bonds to it were broken or formed. However, the stereochemical configuration at the chiral center at C1 changes as bonds to it are affected throughout the course of reaction. This will change the stereochemical configuration at C3 chiral carbon atom. Thus, a single stereoisomer will be generated.

Conclusion

For the given ${\text{S}}_{\text{N}}2$ reaction, the complete and detailed mechanism and products are shown above.

Interpretation Introduction

(c)

Interpretation:

The complete, detailed mechanism and products for the given reaction are to be drawn assuming that it takes place via an ${\text{S}}_{\text{N}}2$ mechanism, paying attention to stereochemistry.

Concept introduction:

${\text{S}}_{\text{N}}2$ reaction is the bimolecular nucleophilic substitution reaction. The halide group in the substrate acts as a good leaving group. In an ${\text{S}}_{\text{N}}2$ reaction, the incoming nucleophile attacks the carbon that is bonded to the leaving group, with the leaving group breaking off simultaneously with its bond pair. The incoming group must attack the carbon from a direction opposite the leaving group. The result is generally a single product. As ${\text{S}}_{\text{N}}2$  reaction is a single-step reaction, the stereo-specificity suggests that the nucleophile attacks the substrate exclusively from the side opposite the leaving group, producing a single stereoisomer. Thus, ${\text{S}}_{\text{N}}2$  reactions are stereospecific.

Answer to Problem 8.13P

The complete, detailed mechanism for the given reaction, assuming that it takes place via an ${\text{S}}_{\text{N}}2$ mechanism, paying attention to stereochemistry, is

Explanation of Solution

The given reaction is

The reactant molecule contains one chiral center. The leaving group is ${\text{Br}}^{-}$, and the nucleophile is ${{\text{(C}}_{\text{6}}{\text{H}}_{\text{5}}\text{)}}_{\text{3}}\text{P:}$. In an ${\text{S}}_{\text{N}}2$ reaction, the ${{\text{(C}}_{\text{6}}{\text{H}}_{\text{5}}\text{)}}_{\text{3}}\text{P:}$ nucleophile should attack from the side opposite the $\text{C-Br}$ bond, in this case, from behind the plane of the page. Thus, the new ${\text{C-(C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{)}}_{\text{3}}\text{P}$ bond remains behind the plane of the page attached by a dash bond. Complete and detailed mechanism of the given reaction is as follows:

Note that, the stereochemical configuration at the chiral center changes as bonds to it ae affected throughout the course of reaction. This will change the stereochemical configuration at the chiral center, and it will be opposite than the reactant molecule. Thus, a single stereoisomer will be generated.

Conclusion

For the given ${\text{S}}_{\text{N}}2$ reaction, the complete and detailed mechanism and products are shown above.