Chapter 11, Problem 11.39P

Interpretation Introduction

(a)

Interpretation:

The detailed mechanism for the production of given compounds from the respective alkyne is to be drawn.

Concept introduction:

The alkynes are electron rich system like alkenes and can undergo an electrophilic addition reaction with strong Bronsted acids just like the alkenes do. The reaction proceeds with proton transfer reaction to form a stable carbocation followed by the action of water as a nucleophile. In excess of reagent, the reaction occurs twice forming a geminal dihalide compound as a major product.

Answer to Problem 11.39P

The detailed mechanism for the given reaction with a major product is:

Explanation of Solution

The structure for the given compound $\text{(1, 1-Dichloro-2-cyclopentylethyl)benzene}$ is:

The given compound is germinal dichloride, and thus can be produced by electrophilic addition of an excess of $\text{HCl}$. The reaction with the respective alkyne is shown below:

In the given reaction the alkyne is the electron rich site and the hydrogen from the $\text{HCl}$ is the electron poor site. Thus the first step is the addition of ${\text{H}}^{\text{+}}$ across the $\text{C}\equiv \text{C}$ bond and forms carbocation at benzylic position which is resonance stabilized therefore more stable.

In the second step, the chloride ion acts as a nucleophile and attacks at vinylic carbocation forming vinylic chloride product.

The vinylic chloride again undergoes the addition of ${\text{H}}^{\text{+}}$ across the $\text{C}=\text{C}$ bond and forms more stable carbocation.

This carbocation further reacts with nucleophilic chloride ion to form a germinal dichloride product.

Conclusion

The detailed mechanism is drawn for the given reaction with showing the formation of stable carbocations and major product.

Interpretation Introduction

(b)

Interpretation:

The detailed mechanism for the production of given compounds from respective alkyne is to be drawn.

Concept introduction:

The alkynes are electron rich system like alkenes and can undergo an electrophilic addition reaction with strong Bronsted acids just like the alkenes do. The reaction proceeds with proton transfer reaction to form a stable carbocation followed by the action of water as a nucleophile. In excess of reagent, the reaction occurs twice forming a geminal dihalide compound as a major product.

Answer to Problem 11.39P

The detailed mechanism for the given reaction with the major product is:

Explanation of Solution

The structure for the given compound $\text{3, 3-Dibromohexane}$ is:

The given compound is germinal dibromide, thus can be produced by electrophilic addition of an excess of $\text{HBr}$. The reaction with the respective alkyne is shown below:

In the given reaction the alkyne is the electron rich site and the hydrogen from the $\text{HBr}$ is the electron poor site. Thus the first step is the addition of ${\text{H}}^{\text{+}}$ across the $\text{C}\equiv \text{C}$ bond and forms vinylic carbocation.

In the second step, the bromide ion acts as a nucleophile and attacks at vinylic carbocation forming vinylic bromide product.

The vinylic bromide again undergoes the addition of ${\text{H}}^{\text{+}}$ across the $\text{C}=\text{C}$ bond and forms more stable carbocation.

This carbocation further reacts with nucleophilic bromide ion to form germinal dibromide product.

Conclusion

The detailed mechanism is drawn for the given reaction with showing the formation of stable carbocations and major product.

Interpretation Introduction

(c)

Interpretation:

The detailed mechanism for the production of given compounds from respective alkyne is to be drawn.

Concept introduction:

The alkynes are electron rich system like alkenes and can undergo an electrophilic addition reaction with strong Bronsted acids just like the alkenes do. The reaction proceeds with proton transfer reaction to form a stable carbocation followed by the action of water as a nucleophile. In a single addition reaction, the reaction occurs only once forming a vibylic halide compound as a major product. The deuterium is an isotope of a hydrogen atom and reacts the same as hydrogen.

Answer to Problem 11.39P

The detailed mechanism for the given reaction with a major product is:

Explanation of Solution

The structure for the given compound is:

The given compound is vinylic bromide having deuterium at adjacent carbon, thus can be produced by single electrophilic addition of $\text{DBr}$. The reaction with the respective alkyne is shown below:

In the given reaction the alkyne is the electron rich site and the hydrogen from the $\text{DBr}$ is the electron poor site. Thus the first step is the addition of ${\text{D}}^{\text{+}}$ across the $\text{C}\equiv \text{C}$ bond and forms vinylic carbocation.

In the second step the bromide ion acts as a nucleophile and attacks at vinylic carbocation forming vinylic bromide product.

Conclusion

The detailed mechanism is drawn for the given reaction with showing the formation of stable carbocations and major product.

Interpretation Introduction

(d)

Interpretation:

The detailed mechanism for the production of given compounds from respective alkyne is to be drawn.

Concept introduction:

The alkynes are electron rich system like alkenes and can undergo an electrophilic addition reaction with strong Bronsted acids just like the alkenes do. The reaction proceeds with proton transfer reaction to form a stable carbocation followed by the action of water as a nucleophile. In excess of reagent, the reaction occurs twice forming a geminal dihalide compound as a major product.

Answer to Problem 11.39P

The detailed mechanism for the given reaction with the major product is:

Explanation of Solution

The structure for the given compound is:

The given compound is germinal dichloride, thus can be produced by electrophilic addition of an excess of $\text{HCl}$. The reaction with the respective alkyne is shown below:

In the given reaction the alkyne is the electron rich site and the hydrogen from the $\text{HCl}$ is the electron poor site. Thus the first step is the addition of ${\text{H}}^{\text{+}}$ across the $\text{C}\equiv \text{C}$ bond and forms carbocation at a benzylic position which is resonance stabilized therefore more stable.

In the second step, the chloride ion acts as a nucleophile and attacks at vinylic carbocation forming vinylic chloride products.

The vinylic chloride again undergoes the addition of ${\text{H}}^{\text{+}}$ across the $\text{C}=\text{C}$ bond and forms more stable carbocation.

This carbocation further reacts with nucleophilic chloride ion to form a germinal dichloride product.

Conclusion

The detailed mechanism is drawn for the given reaction with showing the formation of stable carbocations and major product.