Chapter 9, Problem 9.64P

Interpretation Introduction

(a)

Interpretation:

The complete, detailed mechanism for the reaction is to be provided. The stereochemistry of the products is to be predicted where appropriate. If the reaction yields exclusively one product or a mixture of products, then the major product is to be determined.

Concept introduction:

For the prediction of the outcome of the ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, four factors are considered. First, determine if the substrate molecule has a good leaving group. For the prediction of ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, the leaving groups must be stable. Next, the carbon atom attached to the leaving group needs to be ${\text{sp}}^{\text{3}}$ hybridized. After that, if the leaving group is attached to a primary carbon, then ${\text{S}}_{\text{N}}\text{1 and E1}$ reactions are not feasible unless the resulting carbocation is resonance stabilized. If the leaving group is bonded to the tertiary carbon, then ${\text{S}}_{\text{N}}\text{2}$ reactions are not feasible. If it is attached to a secondary carbon atom, then all four reactions are likewise possible. Next, examine the influence of the strength of the nucleophile, concentrations of the attacking species, the ability of the leaving group, and the effect of the solvent. Finally, if all ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions appear to be favored, then heat is the influencing factor. Elimination reactions are favored at higher temperatures, and substitutions reactions are carried at low temperatures.

Answer to Problem 9.64P

The complete, detailed mechanism for the reaction is shown below:

Explanation of Solution

The given reaction is

The absolute configuration of the substrate is S. This is solvolysis reaction because ethanol acts as a nucleophile and a solvent. The leaving group, ${}^{\text{-}}\text{OTs}$, is a good leaving group. So it is suitable for nucleophilic substitution and elimination reaction. ${}^{\text{-}}\text{OTs}$ is attached on the secondary carbon, so we consider all four ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ mechanisms.

The attacking species ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$ is a weak nucleophile and weak base favoring ${\text{S}}_{\text{N}}\text{1 and E1}$ reactions. The concentrations of the weak base do not matter. ${}^{\text{-}}\text{OTs}$ is an excellent leaving group, which favors ${\text{S}}_{\text{N}}\text{1}$. Finally, the solvent ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$ is a polar protic solvent, which also favors ${\text{S}}_{\text{N}}\text{1}$. In the given reaction, heat is not provided, so substitution is more favored than elimination. So, ${\text{S}}_{\text{N}}\text{1}$ mechanism is the predominant mechanism for the given reaction.

The loss of the leaving group, ${}^{\text{-}}\text{OTs}$, produces a secondary carbocation.

A tertiary carbocation is highest stability than a secondary and primary carbocation. Next, $\text{1, 2-methyl}$ shift takes place to produce a more stable carbocation.

Now, the weak nucleophile, ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$ attacks the carbocation to produce the substitution product.

Finally, deprotonation of the ${\text{S}}_{\text{N}}\text{1}$ product takes place to yield an uncharged substitution product.

The detailed, complete mechanism is as follows:

Conclusion

The outcome of the given reaction is predicted by considering factors like the nature of the leaving group, substrate, the strength of the reagent used, solvent, and temperature.

Interpretation Introduction

(b)

Interpretation:

The complete, detailed mechanism for the reaction is to be provided. The stereochemistry of the products is to be predicted where appropriate. If the reaction yields exclusively one product or a mixture of products, then the major product is to be determined.

Concept introduction:

For the prediction of the outcome of the ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, four factors are considered. First, determine if the substrate molecule has a good leaving group. For the prediction of ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, the leaving groups must be stable. Next, the carbon atom attached to the leaving group needs to be ${\text{sp}}^{\text{3}}$ hybridized. After that, if the leaving group is attached to a primary carbon, then ${\text{S}}_{\text{N}}\text{1 and E1}$ reactions are not feasible unless the resulting carbocation is resonance stabilized. If the leaving group is bonded to the tertiary carbon, then ${\text{S}}_{\text{N}}\text{2}$ reactions are not feasible. If it is attached to a secondary carbon atom, then all four reactions are likewise possible. Next, examine the influence of the strength of the nucleophile, concentrations of the attacking species, the ability of the leaving group, and the effect of the solvent. Finally, if all ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions appear to be favored, then heat is the influencing factor. Elimination reactions are favored at higher temperatures, and substitutions reactions are carried at low temperatures.

Answer to Problem 9.64P

The complete, detailed mechanism for the reaction is shown below:

The stereochemistry of the product is R configuration.

Explanation of Solution

The given reaction is

The absolute configuration of the substrate is S. The leaving group, ${}^{\text{-}}\text{OTs}$, is a good leaving group. So it is suitable for nucleophilic substitution and elimination reaction. ${}^{\text{-}}\text{OTs}$ is attached on the secondary carbon, so we consider all four ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ mechanisms.

The attacking species ${\text{CN}}^{\text{-}}$ is a strong nucleophile and weak base, favoring ${\text{S}}_{\text{N}}\text{2 and E1}$ reactions. The high concentration of the weak base favors ${\text{S}}_{\text{N}}\text{2}$ mechanism. ${}^{\text{-}}\text{OTs}$ is an excellent leaving group, which favors ${\text{S}}_{\text{N}}\text{1 and E1}$. Finally, the solvent DMF is a polar aprotic solvent, which also favors ${\text{S}}_{\text{N}}\text{2 and E2}$. In the given reaction, heat is not provided, so substitution is more favored than elimination. So, ${\text{S}}_{\text{N}}2$ mechanism is the predominant mechanism for the given reaction.

The carbon atom attached to the leaving group is a chiral center. ${\text{CN}}^{\text{-}}$ is a strong nucleophile, and a backside attack on the carbon leads to an inversion of stereochemistry.

The stereochemistry of the product is R configuration.

Conclusion

The outcome of the given reaction is predicted by considering factors like the nature of the leaving group, substrate, the strength of the reagent used, solvent, and temperature.

Interpretation Introduction

(c)

Interpretation:

The complete, detailed mechanism for the reaction is to be provided. The stereochemistry of the products is to be predicted where appropriate. If the reaction yields exclusively one product or a mixture of products, then the major product is to be determined.

Concept introduction:

For the prediction of the outcome of the ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, four factors are considered. First, determine if the substrate molecule has a good leaving group. For the prediction of ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, the leaving groups must be stable. Next, the carbon atom attached to the leaving group needs to be ${\text{sp}}^{\text{3}}$ hybridized. After that, if the leaving group is attached to a primary carbon, then ${\text{S}}_{\text{N}}\text{1 and E1}$ reactions are not feasible unless the resulting carbocation is resonance stabilized. If the leaving group is bonded to the tertiary carbon, then ${\text{S}}_{\text{N}}\text{2}$ reactions are not feasible. If it is attached to a secondary carbon atom, then all four reactions are likewise possible. Next, examine the influence of the strength of the nucleophile, concentrations of the attacking species, the ability of the leaving group, and the effect of the solvent. Finally, if all ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions appear to be favored, then heat is the influencing factor. Elimination reactions are favored at higher temperatures, and substitutions reactions are carried at low temperatures.

Answer to Problem 9.64P

The complete, detailed mechanism for the reaction is shown below:

Explanation of Solution

The given reaction is

The absolute configuration of the substrate is S. The leaving group, ${}^{\text{-}}\text{OTs}$, is a good leaving group. So it is suitable for nucleophilic substitution and elimination reaction. ${}^{\text{-}}\text{OTs}$ is attached on the secondary carbon, so we consider all four ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ mechanisms.

The attacking species ${{\text{(CH}}_{\text{3}}\text{)}}_{\text{3}}{\text{CO}}^{\text{-}}$ is a strong and bulky nucleophile, favoring $\text{E2}$ mechanism. The high concentration of the attacking species favors $\text{E2}$ over the $\text{E1}$ mechanism. Normally alkoxide favor ${\text{S}}_{\text{N}}2$ and $\text{E2}$, but because of the excessive bulkiness of ${{\text{(CH}}_{\text{3}}\text{)}}_{\text{3}}{\text{CO}}^{\text{-}}$ species, it favors only the $\text{E2}$ reaction. ${}^{\text{-}}\text{OTs}$ is an excellent leaving group, which favors ${\text{S}}_{\text{N}}\text{1 and E1}$. Finally, the solvent DMSO is a polar aprotic solvent, which also favors ${\text{S}}_{\text{N}}\text{2 and E2}$. In the given reaction, heat is not provided, so substitution is more favored than elimination. So, the $\text{E2}$ mechanism is the predominant mechanism for the given reaction.

In the substrate, the alpha C atom has one H atom attached to it. Since ${{\text{(CH}}_{\text{3}}\text{)}}_{\text{3}}{\text{CO}}^{\text{-}}$ is a strong and bulky nucleophile, it abstracts the H atom from the terminal C atom and yields alkene as the major product.

Conclusion

The outcome of the given reaction is predicted by considering factors like the nature of the leaving group, substrate, the strength of the reagent used, solvent, and temperature.

Interpretation Introduction

(d)

Interpretation:

The complete, detailed mechanism for the reaction is to be provided. The stereochemistry of the products is to be predicted where appropriate. If the reaction yields exclusively one product or a mixture of products, then the major product is to be determined.

Concept introduction:

For the prediction of the outcome of the ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, four factors are considered. First, determine if the substrate molecule has a good leaving group. For the prediction of ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, the leaving groups must be stable. Next, the carbon atom attached to the leaving group needs to be ${\text{sp}}^{\text{3}}$ hybridized. After that, if the leaving group is attached to a primary carbon, then ${\text{S}}_{\text{N}}\text{1 and E1}$ reactions are not feasible unless the resulting carbocation is resonance stabilized. If the leaving group is bonded to the tertiary carbon, then ${\text{S}}_{\text{N}}\text{2}$ reactions are not feasible. If it is attached to a secondary carbon atom, then all four reactions are likewise possible. Next, examine the influence of the strength of the nucleophile, concentrations of the attacking species, the ability of the leaving group, and the effect of the solvent. Finally, if all ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions appear to be favored, then heat is the influencing factor. Elimination reactions are favored at higher temperatures, and substitutions reactions are carried at low temperatures.

Answer to Problem 9.64P

The complete, detailed mechanism for the reaction is shown below:

Explanation of Solution

The given reaction is

The absolute configuration of the substrate is S. The leaving group, ${}^{\text{-}}\text{OTs}$, is a good leaving group. So it is suitable for nucleophilic substitution and elimination reaction. $\text{-OTs}$ is attached on the secondary carbon, so we consider all four ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ mechanisms.

The attacking species ${\text{CO}}_{\text{3}}{}^{\text{2-}}$ is a weak nucleophile and weak base, favoring ${\text{S}}_{\text{N}}\text{1 and E1}$ reactions. The concentration of the weak base does not matter. ${}^{\text{-}}\text{OTs}$ is an excellent leaving group, which favors ${\text{S}}_{\text{N}}\text{1 and E1}$. Finally, the solvent ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$ is a polar protic solvent, which also favors ${\text{S}}_{\text{N}}\text{1 and E1}$. In the given reaction, heat is provided, so elimination is more favored than substitution. So, the $\text{E1}$ mechanism is the predominant mechanism for the given reaction.

The loss of the leaving group, ${}^{\text{-}}\text{OTs}$, produces a secondary carbocation.

A tertiary carbocation is greatest stability than a secondary and primary carbocation. Next, $\text{1, 2-methyl}$ shift takes place to produce a more stable carbocation.

Now, the weak nucleophile ${\text{CO}}_{\text{3}}{}^{\text{2-}}$ abstracts the highly substituted proton and produces the most highly substituted alkene.

The detailed, complete mechanism is as follows:

Conclusion

The outcome of the given reaction is predicted by considering factors like the nature of the leaving group, substrate, the strength of the reagent used, solvent, and temperature.

Interpretation Introduction

(e)

Interpretation:

The complete, detailed mechanism for the reaction is to be provided. The stereochemistry of the products is to be predicted where appropriate. If the reaction yields exclusively one product or a mixture of products, then the major product is to be determined.

Concept introduction:

For the prediction of the outcome of the ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, four factors are considered. First, determine if the substrate molecule has a good leaving group. For the prediction of ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, the leaving groups must be stable. Next, the carbon atom attached to the leaving group needs to be ${\text{sp}}^{\text{3}}$ hybridized. After that, if the leaving group is attached to a primary carbon, then ${\text{S}}_{\text{N}}\text{1 and E1}$ reactions are not feasible unless the resulting carbocation is resonance stabilized. If the leaving group is bonded to the tertiary carbon, then ${\text{S}}_{\text{N}}\text{2}$ reactions are not feasible. If it is attached to a secondary carbon atom, then all four reactions are likewise possible. Next, examine the influence of the strength of the nucleophile, concentrations of the attacking species, the ability of the leaving group, and the effect of the solvent. Finally, if all ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions appear to be favored, then heat is the influencing factor. Elimination reactions are favored at higher temperatures, and substitutions reactions are carried at low temperatures.

Answer to Problem 9.64P

The complete, detailed mechanism for the reaction is shown below:

Explanation of Solution

The given reaction is

This is a solvolysis reaction because ethanol acts as a nucleophile and the solvent. The leaving group, ${\text{Cl}}^{\text{-}}$, is a good leaving group. So it is suitable for nucleophilic substitution and elimination reaction. ${\text{Cl}}^{\text{-}}$ is attached on the tertiary carbon, so we consider three mechanisms -- ${\text{S}}_{\text{N}}\text{1, E2, and E1}$ -- and rule out ${\text{S}}_{\text{N}}\text{2}$.

The attacking species ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$ is a weak nucleophile and weak base favoring ${\text{S}}_{\text{N}}\text{1 and E1}$ reactions. The concentration of the attacking species does not matter. ${\text{Cl}}^{\text{-}}$ is moderate leaving group, which favors all four reactions. Finally, the solvent ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$ is a polar protic solvent, which also favors ${\text{S}}_{\text{N}}\text{1 and E1}$. In the given reaction, heat is provided, so elimination is more favored than substitution. So, the $\text{E1}$ mechanism is the predominant mechanism for the given reaction.

The loss of the leaving group, ${\text{Cl}}^{\text{-}}$, produces a tertiary carbocation.

Now, the weak nucleophile ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}$ abstracts the proton from the terminal ${\text{CH}}_{\text{3}}$ group and produces the most highly substituted alkene.

The detailed, complete mechanism is as follows:

Conclusion

The outcome of the given reaction is predicted by considering factors like the nature of the leaving group, substrate, the strength of the reagent used, solvent, and temperature.

Interpretation Introduction

(f)

Interpretation:

The complete, detailed mechanism for the reaction is to be provided. The stereochemistry of the products is to be predicted where appropriate. If the reaction yields exclusively one product or a mixture of products, then the major product is to be determined.

Concept introduction:

For the prediction of the outcome of the ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, four factors are considered. First, determine if the substrate molecule has a good leaving group. For the prediction of ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions, the leaving groups must be stable. Next, the carbon atom attached to the leaving group needs to be ${\text{sp}}^{\text{3}}$ hybridized. After that, if the leaving group is attached to a primary carbon, then ${\text{S}}_{\text{N}}\text{1 and E1}$ reactions are not feasible unless the resulting carbocation is resonance stabilized. If the leaving group is bonded to the tertiary carbon, then ${\text{S}}_{\text{N}}\text{2}$ reactions are not feasible. If it is attached to a secondary carbon atom, then all four reactions are likewise possible. Next, examine the influence of the strength of the nucleophile, concentrations of the attacking species, the ability of the leaving group, and the effect of the solvent. Finally, if all ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ reactions appear to be favored, then heat is the influencing factor. Elimination reactions are favored at higher temperatures, and substitutions reactions are carried at low temperatures.

Answer to Problem 9.64P

The complete, detailed mechanism for the reaction is shown below:

Explanation of Solution

The given reaction is

The leaving group, ${\text{Cl}}^{\text{-}}$, is a suitable leaving group. So it is suitable for nucleophilic substitution and elimination reaction. ${\text{Cl}}^{\text{-}}$ is attached on the secondary carbon, so we consider all four ${\text{S}}_{\text{N}}{\text{2, S}}_{\text{N}}\text{1, E2, and E1}$ mechanisms.

The attacking species ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{O}}^{\text{-}}$ is a strong nucleophile and strong base, favoring ${\text{S}}_{\text{N}}2$ and $\text{E2}$ reactions. The high concentration of the attacking species favors ${\text{S}}_{\text{N}}2$ and $\text{E2}$ mechanisms. ${\text{Cl}}^{\text{-}}$ is a moderated leaving group, which favors all four reactions. Finally, the solvent DMSO is a polar aprotic solvent, which also favors ${\text{S}}_{\text{N}}\text{2 and E2}$. In the given reaction, heat is provided, so elimination is more favored than substitution. So, the $\text{E2}$ mechanism is the predominant mechanism for the given reaction.

In the substrate, only one H atom can be eliminated. The leaving group and H atom are on same side. $\text{E2}$ mechanism favors the anticoplanar conformation of the H and the leaving group. So, the bond rotation is carried between the C attached to the leaving group and the C attached to the H atom.

The base deprotonates a hydrogen atom from the substrate and to yield the most substituted alkene as the product.

The detailed, complete mechanism is as follows:

Conclusion

The outcome of the given reaction is predicted by considering factors like the nature of the leaving group, substrate, the strength of the reagent used, solvent, and temperature.