Chapter 12, Problem 12.44P

Interpretation Introduction

(a)

Interpretation:

It is to be explained whether the given transformation would be a result of acid-catalyzed hydration or oxymercuration-reduction.

Concept introduction:

The acid-catalyzed hydration of an alkene is the electrophilic addition of water across the $\text{C=C}$ bond in an acidic condition. The electrophilic addition reaction of an alkene occurs through formation of a more stable carbocation. The reaction proceeds with proton transfer reaction to form a stable carbocation, followed by the action of water as a nucleophile, forming the corresponding alcohol. The order of stability of carbocation is ${\text{CH}}_{\text{3}}\text{}{\text{< 1}}^{\text{o}}{\text{ < 2}}^{\text{o}}{\text{ < 3}}^{\text{o}}$. The carbocation can be rearranged by $\text{1, 2-}$ hydride or $\text{1, 2-}$ methyl shift to form a more stable carbocation.

The oxymercuration-reduction is also the reaction of addition of water through the $\text{C=C}$ bond. The alkene is first reacted with mercury $\left(\text{II}\right)$ acetate, $\text{Hg}{\left(\text{OAc}\right)}_{\text{2}}$, in water–tetrahydrofuran (THF) solution, and that is followed by reduction with sodium borohydride, ${\text{NaBH}}_{\text{4}}$. The mechanism follows the Markovnikov rule and adds $\text{OH}$ to more substituted double bonded carbon. The reaction proceeds through formation of a Mercurinium ion intermediate, and there is no formation of a carbocation. Thus, the rearrangement is not possible in oxymercuration-reduction.

Answer to Problem 12.44P

The given transformation can be carried out by oxymercuration-reduction. The detailed mechanism is as follows:

Explanation of Solution

The given equation is

In the substrate, the alkene $\text{C=C}$ bond is terminal, and the product has $\text{OH}$ bonded to the same carbon where $\text{C=C}$ was present in the substrate. It suggests that the reaction occurred without rearrangement. This indicates that the reaction would have occurred by oxymercuration-reduction and not by the acid catalyzed hydration, which proceeds through rearrangement by formation of the benzylic carbocation.

The alkene substrate, on reaction with mercury $\left(\text{II}\right)$ acetate, $\text{Hg}{\left(\text{OAc}\right)}_{\text{2}}$ in water, followed by ${\text{NaBH}}_{\text{4}}$ in ethanol, undergoes oxymercuration-reduction.

In the first step, the electron rich $\text{C=C}$ bond of the alkene attacks the electrophilic $\text{Hg}$ whose electron pair forms a bond with carbon, producing a three-membered ring called mercurinium ion intermediate.

In the second step, the water molecule acts as a nucleophile on one of the carbons of the three-membered ring to open the ring, followed by deprotonation of the positively charged oxygen atom.

The product formed in the previous step is then subjected to reduction with sodium borohydride, ${\text{NaBH}}_{\text{4}}$, where the substituent $\text{HgOAc}$ is replaced by $\text{H}$.

Conclusion

The preparation of the given compound is explained indicating the addition of water across the $\text{C=C}$ double bond occurring through oxymercuration-reduction.

Interpretation Introduction

(b)

Interpretation:

It is to be explained whether the given transformation would be a result of acid-catalyzed hydration or oxymercuration-reduction.

Concept introduction:

The acid-catalyzed hydration of an alkene is the electrophilic addition of water across the $\text{C=C}$ bond in an acidic condition. The electrophilic addition reaction of an alkene occurs through formation of a more stable carbocation. The reaction proceeds with proton transfer reaction to form a stable carbocation, followed by the action of water as a nucleophile, forming the corresponding alcohol. The order of stability of carbocation is ${\text{CH}}_{\text{3}}\text{}{\text{< 1}}^{\text{o}}{\text{ < 2}}^{\text{o}}{\text{ < 3}}^{\text{o}}$. The carbocation can be rearranged by $\text{1, 2-}$ hydride or $\text{1, 2-}$ methyl shift to form a more stable carbocation.

The oxymercuration-reduction is also the reaction of addition of water through the $\text{C=C}$ bond. The alkene is first reacted with mercury $\left(\text{II}\right)$ acetate, $\text{Hg}{\left(\text{OAc}\right)}_{\text{2}}$, in water–tetrahydrofuran (THF) solution, and that is followed by reduction with sodium borohydride, ${\text{NaBH}}_{\text{4}}$. The mechanism follows the Markovnikov rule and adds $\text{OH}$ to more substituted double bonded carbon. The reaction proceeds through formation of a Mercurinium ion intermediate, and there is no formation of a carbocation. Thus, the rearrangement is not possible in oxymercuration-reduction.

Answer to Problem 12.44P

The given transformation can be carried out by acid-catalyzed hydration. The detailed mechanism is as follows:

Explanation of Solution

The given equation is

In the substrate, the alkene $\text{C=C}$ bond is terminal, and the product has $\text{OH}$ bonded to the same carbon where $\text{C=C}$ was present in the substrate. It suggests that the reaction occurred without rearrangement. This indicates that the reaction would have occurred by oxymercuration-reduction and not by the acid catalyzed hydration, which proceeds through rearrangement by formation of the benzylic carbocation (resonance stabilized carbocation).

The first step is the formation of a secondary carbocation by proton transfer reaction. The proton transfers to the less substituted double bonded carbon.

The secondary carbocation can be rearranged to more stable tertiary as well as resonance stabilized carbocation by $\text{1, 2-}$ hydride shift.

In the second step, the water molecule acts as a nucleophile on one of the carbons of the three-membered ring to open the ring, followed by deprotonation of the positively charged oxygen atom.

Conclusion

The detailed mechanism for the given reaction is drawn by suggesting that the reaction occurred through carbocation rearrangement.

Interpretation Introduction

(c)

Interpretation:

It is to be explained whether the given transformation would be a result of acid-catalyzed hydration or oxymercuration-reduction.

Concept introduction:

The acid-catalyzed hydration of an alkene is the electrophilic addition of water across the $\text{C=C}$ bond in an acidic condition. The electrophilic addition reaction of an alkene occurs through formation of a more stable carbocation. The reaction proceeds with proton transfer reaction to form a stable carbocation, followed by the action of water as a nucleophile, forming the corresponding alcohol. The order of stability of carbocation is ${\text{CH}}_{\text{3}}\text{}{\text{< 1}}^{\text{o}}{\text{ < 2}}^{\text{o}}{\text{ < 3}}^{\text{o}}$. The carbocation can be rearranged by $\text{1, 2-}$ hydride or $\text{1, 2-}$ methyl shift to form a more stable carbocation.

The oxymercuration-reduction is also the reaction of addition of water through the $\text{C=C}$ bond. The alkene is first reacted with mercury $\left(\text{II}\right)$ acetate, $\text{Hg}{\left(\text{OAc}\right)}_{\text{2}}$, in water–tetrahydrofuran (THF) solution, and that is followed by reduction with sodium borohydride, ${\text{NaBH}}_{\text{4}}$. The mechanism follows the Markovnikov rule and adds $\text{OH}$ to more substituted double bonded carbon. The reaction proceeds through formation of a Mercurinium ion intermediate, and there is no formation of a carbocation. Thus, the rearrangement is not possible in oxymercuration-reduction.

Answer to Problem 12.44P

The given transformation can be carried out by acid catalyzed hydration. The detailed mechanism is as follows:

Explanation of Solution

The given equation is

In the substrate, the alkene $\text{C=C}$ bond is terminal, and the product has $\text{OH}$ bonded to the same carbon where $\text{C=C}$ was present in the substrate. It suggests that the reaction occurred without rearrangement. This indicates that the reaction would have occurred by oxymercuration-reduction and not by the acid catalyzed hydration, which proceeds through rearrangement by formation of the benzylic carbocation (resonance stabilized carbocation).

The first step is the formation of a secondary carbocation by proton transfer reaction. The proton transfers to the less substituted double bonded carbon.

The secondary carbocation can be rearranged to more stable tertiary by $\text{1, 2-}$ hydride shift.

In the second step, the water molecule acts as a nucleophile on one of the carbons of the three-membered ring to open the ring, followed by deprotonation of the positively charged oxygen atom.

Conclusion

The detailed mechanism for the given reaction is drawn by suggesting that the reaction occurred through carbocation rearrangement.

Interpretation Introduction

(d)

Interpretation:

It is to be explained whether the given transformation would be a result of acid-catalyzed hydration or oxymercuration-reduction.

Concept introduction:

The acid-catalyzed hydration of an alkene is the electrophilic addition of water across the $\text{C=C}$ bond in an acidic condition. The electrophilic addition reaction of an alkene occurs through formation of a more stable carbocation. The reaction proceeds with proton transfer reaction to form a stable carbocation, followed by the action of water as a nucleophile, forming the corresponding alcohol. The order of stability of carbocation is ${\text{CH}}_{\text{3}}\text{}{\text{< 1}}^{\text{o}}{\text{ < 2}}^{\text{o}}{\text{ < 3}}^{\text{o}}$. The carbocation can be rearranged by $\text{1, 2-}$ hydride or $\text{1, 2-}$ methyl shift to form a more stable carbocation.

The oxymercuration-reduction is also the reaction of addition of water across the $\text{C=C}$ bond. The alkene is first reacted with mercury $\left(\text{II}\right)$ acetate, $\text{Hg}{\left(\text{OAc}\right)}_{\text{2}}$, in water–tetrahydrofuran (THF) solution, and that is followed by reduction with sodium borohydride, ${\text{NaBH}}_{\text{4}}$. The mechanism follows the Markovnikov rule and adds $\text{OH}$ to more substituted double bonded carbon. The reaction proceeds through formation of a Mercurinium ion intermediate, and there is no formation of a carbocation. Thus, the rearrangement is not possible in oxymercuration-reduction.

Answer to Problem 12.44P

The given transformation can be carried out by oxymercuration-reduction. The detailed mechanism is as follows:

Explanation of Solution

The given equation is

In the substrate, the alkene $\text{C=C}$ bond is terminal, and the product has $\text{OH}$ bonded to the same carbon where $\text{C=C}$ was present in the substrate. It suggests that the reaction occurred without rearrangement. This indicates that the reaction would have occurred by oxymercuration-reduction and not by the acid catalyzed hydration, which proceeds through rearrangement by formation of the benzylic carbocation.

The alkene substrate, on reaction with mercury $\left(\text{II}\right)$ acetate, $\text{Hg}{\left(\text{OAc}\right)}_{\text{2}}$ in water, followed by ${\text{NaBH}}_{\text{4}}$ in ethanol, undergoes oxymercuration-reduction.

In the first step, the electron rich $\text{C=C}$ bond of the alkene attacks the electrophilic $\text{Hg}$ whose electron pair forms a bond with carbon, producing a three-membered ring called mercurinium ion intermediate.

In the second step, the water molecule acts as a nucleophile on one of the carbons of the three-membered ring to open the ring, followed by deprotonation of the positively charged oxygen atom.

The product formed in the previous step is then subjected to reduction with sodium borohydride, ${\text{NaBH}}_{\text{4}}$, where the substituent $\text{HgOAc}$ is replaced by $\text{H}$.

Conclusion

The preparation of the given compound is explained indicating the addition of water across the $\text{C=C}$ double bond occurring through oxymercuration-reduction.