Chapter 13, Problem 13.6P

Interpretation Introduction

(a)

Interpretation:

For the given proposed transforms, it is to be determined whether it leads to a synthetic trap (i.e. will not proceed as planned in the forward direction) or not along with the reasoning.

Concept introduction:

A particular reaction is undone by performing a transform that depends on the specific location in the target molecule where we want the changes to occur. In doing so, we may encounter synthetic traps. A synthetic trap is the proposed mechanism that prevents the reaction to occur in the forward direction as planned. From the reactions used for functional group transformation, and considering the factors like charge stability and strength of the reagent used, one can determine whether the proposed transform leads to a synthetic trap or not.

Answer to Problem 13.6P

The synthesis will proceed as planned. The forward reaction is shown below:

Explanation of Solution

The given proposed transform is:

The target molecule is on the left side. In the target molecule, there are two functional groups present, a cyanide and hydroxyl group. In order to carry out this transform, sodium cyanide ($\text{NaCN}$) can be used as a nucleophile in an ${\text{S}}_{\text{N}}\text{2}$ reaction. The synthesis will proceed as planned as the cyanide ion is not strong enough a base to deprotonate an alcohol. Also, the hydroxyl group is a poor leaving group for an ${\text{S}}_{\text{N}}\text{2}$ reaction. The overall reaction is shown below:

Thus, the proposed transform does not lead to a synthetic trap and will proceed as planned.

Conclusion

The possibility of the forward reaction in the proposed mechanism is determined on the basis of the functional group transformation reactions, charge stability, and strength of the reagents used.

Interpretation Introduction

(b)

Interpretation:

For the given proposed transforms, it is to be determined whether it leads to a synthetic trap (i.e. will not proceed as planned in the forward direction) or not along with the reasoning.

Concept introduction:

A particular reaction is undone by performing a transform that depends on the specific location in the target molecule where we want the changes to occur. In doing so, we may encounter synthetic traps. A synthetic trap is the proposed mechanism that prevents the reaction to occur in the forward direction as planned. From the reactions used for functional group transformation and considering the factors like charge stability and strength of the reagent used, one can determine whether the proposed transform leads to a synthetic trap or not.

Answer to Problem 13.6P

The synthesis will proceed as planned. The forward reaction is shown below:

Explanation of Solution

The given proposed transform is:

The target molecule is on the left side. In the target molecule, there are two functional groups present, ${\text{SH}}^{-}$ and ${\text{OH}}^{-}$ group. In order to carry out this transform, sodium hydrosulfide ($\text{NaSH}$) can be used as a nucleophile in an ${\text{S}}_{\text{N}}\text{2}$ reaction. The synthesis will proceed as planned as hydrosulfide ion is not strong enough a base to deprotonate an alcohol. Also, the hydroxyl group is a poor leaving group for an ${\text{S}}_{\text{N}}\text{2}$ reaction. The overall reaction is shown below:

Thus, the proposed transform does not lead to a synthetic trap and will proceed as planned.

Conclusion

The possibility of the forward reaction in the proposed mechanism is determined on the basis of the functional group transformation reactions, charge stability, and strength of the reagents used.

Interpretation Introduction

(c)

Interpretation:

For the given proposed transforms, it is to be determined whether it leads to a synthetic trap (i.e. will not proceed as planned in the forward direction) or not along with the reasoning.

Concept introduction:

A particular reaction is undone by performing a transform that depends on the specific location in the target molecule where we want the changes to occur. In doing so, we may encounter synthetic traps. A synthetic trap is the proposed mechanism that prevents the reaction to occur in the forward direction as planned. From the reactions used for functional group transformation, and considering the factors like charge stability and strength of the reagent used, one can determine whether the proposed transform leads to a synthetic trap or not.

Answer to Problem 13.6P

The synthesis will proceed as planned. The forward reaction is shown below:

Explanation of Solution

The given proposed transform is:

The target molecule is on the left side. In the target molecule, there are two functional groups present, alkyl halide and hydroxyl group. Alkyl halides are prepared from corresponding alcohols when they are treated with phosphorous bromide/chloride in an ${\text{S}}_{\text{N}}\text{2}$ reaction. In this reaction, the bromine ${\text{OH}}^{-}$ group will be replaced by bromine or chlorine atom. In order to carry out this transform, phosphorous bromide (${\text{PBr}}_3$) is used that replaces ${\text{OH}}^{-}$ by bromine atom. The other hydroxyl group will not be replaced as it is directly attached to the benzene ring, so it does not undergo ${\text{S}}_{\text{N}}\text{2}$ reaction easily. Also, ${\text{S}}_{\text{N}}\text{2}$ reaction does not take place on an ${\text{sp}}^2$ hybridized carbon atom. Thus, the synthesis will proceed as planned. The overall reaction is shown below:

Thus, the proposed transform does not lead to a synthetic trap and will proceed as planned.

Conclusion

The possibility of the forward reaction in the proposed mechanism is determined on the basis of the functional group transformation reactions, charge stability, and strength of the reagents used.

Interpretation Introduction

(d)

Interpretation:

For the given proposed transforms, it is to be determined whether it leads to a synthetic trap (i.e. will not proceed as planned in the forward direction) or not along with the reasoning.

Concept introduction:

A particular reaction is undone by performing a transform that depends on the specific location in the target molecule where we want the changes to occur. In doing so, we may encounter synthetic traps. A synthetic trap is the proposed mechanism that prevents the reaction to occur in the forward direction as planned. From the reactions used for functional group transformation, and considering the factors like charge stability and strength of the reagent used, one can determine whether the proposed transform leads to the synthetic trap or not.

Answer to Problem 13.6P

The synthesis will not proceed as planned.

The proposed synthesis is a synthetic trap, and the reaction will not proceed as planned in the forward direction.

Explanation of Solution

The given proposed transform is:

The target molecule is on the left side while the proposed reactant molecule is on the right side. In the target molecule, there are two functional groups present, alcohol and alkyl halide. Alkyl halides are prepared from corresponding alcohols when they are treated with phosphorous bromide/chloride in an ${\text{S}}_{\text{N}}\text{2}$ reaction. We could attempt to convert the $\text{OH}$ group to $\text{Br}$ using the reagent ${\text{PBr}}_3$, but in doing so, both $\text{OH}$ groups could be converted as both are attached to an ${\text{sp}}^3$ hybridized carbon atoms. So, this can be a synthetic trap. However, the intended product would be the major product because the functional group is on a primary carbon. The other is on a secondary carbon, which impends ${\text{S}}_{\text{N}}\text{2}$ reactions. As the reaction does not yield the desired product, we would say that the proposed synthesis is a synthetic trap, and the reaction will not proceed as planned in the forward direction.

Conclusion

The possibility of the forward reaction in the proposed mechanism is determined on the basis of the functional group transformation reactions, charge stability, and strength of the reagents used.

Interpretation Introduction

(e)

Interpretation:

For the given proposed transforms, it is to be determined whether it leads to a synthetic trap (i.e. will not proceed as planned in the forward direction) or not along with the reasoning.

Concept introduction:

A particular reaction is undone by performing a transform that depends on the specific location in the target molecule where we want the changes to occur. In doing so, we may encounter synthetic traps. A synthetic trap is the proposed mechanism that prevents the reaction to occur in the forward direction as planned. From the reactions used for functional group transformation, and considering the factors like charge stability and strength of the reagent used, one can determine whether the proposed transform leads to the synthetic trap or not.

Answer to Problem 13.6P

The synthesis will not proceed as planned.

The proposed synthesis is a synthetic trap, and the reaction will not proceed as planned in the forward direction.

Explanation of Solution

The given proposed transform is:

The target molecule is on the left side while the proposed reactant molecule is on the right side. In the target molecule, there are two functional groups present, ether and alkyl halide. Alkyl halides are prepared from alkenes via electrophilic addition of a Bronsted acid across the carbon-carbon double bond. Thus, in the above reaction, in order to convert the alkene into alkyl chloride, hydrochloric acid can be used. In this reaction, the chlorine atom will be added to the most substituted carbon atom. However, the oxygen In ether is likely to protonate in the presence of the strong acid, hydrochloric acid and could lead to an ${\text{S}}_{\text{N}}\text{2}$ reaction in which the chlorine atom opens the protonated ether ring.

As the reaction does not yield the desired product, we would say that the proposed synthesis is a synthetic trap, and the reaction will not proceed as planned in the forward direction.

Conclusion

The possibility of the forward reaction in the proposed mechanism is determined on the basis of the functional group transformation reactions, charge stability, and strength of the reagents used.

Interpretation Introduction

(f)

Interpretation:

For the given proposed transforms it is to be determined whether it leads to a synthetic trap (i.e. will not proceed as planned in the forward direction) or not along with the reasoning.

Concept introduction:

A particular reaction is undone by performing a transform that depends on the specific location in the target molecule where we want the changes to occur. In doing so, we may encounter synthetic traps. A synthetic trap is the proposed mechanism that prevents the reaction to occur in the forward direction as planned. From the reactions used for functional group transformation, and considering the factors like charge stability and strength of the reagent used, one can determine whether the proposed transform leads to the synthetic trap or not.

Answer to Problem 13.6P

The synthesis will not proceed as planned.

The proposed synthesis is a synthetic trap, and the reaction will not proceed as planned in the forward direction.

Explanation of Solution

The given proposed transform is:

The target molecule is on the left side while the proposed reactant molecule is on the right side. In the target molecule, there are two functional groups present, ketone and alkene. Acid-catalyzed hydration reactions of alkynes leads to the formation of ketone as the product. Oxymercuration-reduction reaction of the alkynes is used to form the internal enol that tautomerizes the ketone. The problem is that an alkene is also reactive under oxymercuration-reduction conditions, and a secondary alcohol would be produced.

As the reaction does not yield the desired product, we would say that, the proposed synthesis is a synthetic trap and the reaction will not proceed as planned in the forward direction.

Conclusion

The possibility of the forward reaction in the proposed mechanism is determined on the basis of the functional group transformation reactions, charge stability, and strength of the reagents used.