Chapter 28, Problem 28.1P

Interpretation Introduction

(a)

Interpretation:

The curved arrow mechanism for the reaction is to be stated and the reaction is to be classified as electrocyclic, cycloaddition, and the sigmatropic reaction. Along with that the number of electrons involved in the reaction is to be stated.

Concept introduction:

In the pericyclic reactions, the bond formation and dissociation occur simultaneously. The pericyclic reaction occurs in a concerted fashion with the cyclic shift of electrons. They are of three types, electrocyclic, cycloaddition and the sigmatropic reactions. They occur in the presence of heat or light.

Answer to Problem 28.1P

The given reaction is an example of an electrocyclic pericyclic reaction. The number of electrons involved in this reaction is six. The curved arrow mechanism is shown below.

Explanation of Solution

The given reaction is an example of an electrocyclic reaction. This is because of in this electrocyclic reaction there is an intramolecular $\text{π}$ electron reaction takes place which leads to the formation of a cyclic ring with the formation of one sigma bond with the loss of one $\text{π}$ bond. The number of electrons involved is counted on the basis of twice the number of curved arrow required to write the complete pericyclic reaction. In this reaction, three arrows are required. Therefore, a total of six electrons is involved in this reaction. The curved arrow mechanism for the given reaction is shown below.

Figure 1

Conclusion

The curved arrow mechanism for the reaction is shown in Figure 1. The reaction is a type of electrocyclic reaction. Along with it, the number of electrons involved in this reaction is six.

Interpretation Introduction

(b)

Interpretation:

The curved arrow mechanism for the reaction is to be stated and the reaction is to be classified as electrocyclic, cycloaddition, and the sigmatropic reaction. Along with that the number of electrons involved in the reaction is to be stated.

Concept introduction:

In the pericyclic reactions, the bond formation and dissociation occur simultaneously. The pericyclic reaction occurs in a concerted fashion with the cyclic shift of electrons. They are of three types electrocyclic, cycloaddition and the sigmatropic reactions. They occur in the presence of heat or light.

Answer to Problem 28.1P

The given reaction is an example of a sigmatropic pericyclic reaction. The number of electrons involved in this reaction is two. The curved arrow mechanism is shown below.

Explanation of Solution

The given reaction is an example of a sigmatropic reaction. This is because of in this sigmatropic reaction the allylic sigma bond present at one end of the system migrate to the other end of the system. The number of $\text{σ}$ and $\text{π}$ bonds remains unchanged during this process. The number of electrons involved is counted on the basis of twice the number of curved arrow required to write the complete pericyclic reaction. In this reaction, one arrow is required. Therefore, a total of two electrons is involved in this reaction. The curved arrow mechanism for the given reaction is shown below.

Figure 2

Conclusion

The curved arrow mechanism for the reaction is shown in Figure 2. The reaction is a type of sigmatropic reaction. Along with it, the number of electrons involved in this reaction is two.

Interpretation Introduction

(c)

Interpretation:

The curved arrow mechanism for the reaction is to be stated and the reaction is to be classified as electrocyclic, cycloaddition, and the sigmatropic reaction. Along with that the number of electrons involved in the reaction is to be stated.

Concept introduction:

In the pericyclic reactions, the bond formation and dissociation occur simultaneously. The pericyclic reaction occurs in a concerted fashion with the cyclic shift of electrons. They are of three types electrocyclic, cycloaddition and the sigmatropic reactions. They occur in the presence of heat or light.

Answer to Problem 28.1P

The given reaction is an example of a cycloaddition pericyclic reaction. The number of electrons involved in this reaction is four. The curved arrow mechanism is shown below.

Explanation of Solution

The given reaction is an example of a cycloaddition reaction. This is because of in this cycloaddition reaction two $\text{π}$ bonds react together to form a cyclic ring with the formation of two $\text{σ}$ bonds. The resulted compound has two fewer $\text{π}$ bonds. The number of electrons involved is counted on the basis of twice the number of curved arrow required to write the complete pericyclic reaction. In this reaction, two arrows are required. Therefore, a total of four electrons is involved in this reaction. The curved arrow mechanism for the given reaction is shown below.

Figure 3

Conclusion

The curved arrow mechanism for the reaction is shown in Figure 3. The reaction is a type of cycloaddition reaction. Along with it, the number of electrons involved in this reaction is four.

Interpretation Introduction

(d)

Interpretation:

The curved arrow mechanism for the reaction is to be stated and the reaction is to be classified as electrocyclic, cycloaddition, and the sigmatropic reaction. Along with that the number of electrons involved in the reaction is to be stated.

Concept introduction:

In the pericyclic reactions, the bond formation and dissociation occur simultaneously. The pericyclic reaction occurs in a concerted fashion with the cyclic shift of electrons. They are of three types electrocyclic, cycloaddition and the sigmatropic reactions. They occur in the presence of heat or light.

Answer to Problem 28.1P

The given reaction is an example of a sigmatropic pericyclic reaction. The number of electrons involved in this reaction is six. The curved arrow mechanism is shown below.

Explanation of Solution

The given reaction is an example of a sigmatropic reaction. This is because of in this sigmatropic reaction the allylic sigma bond present at one end of the $\text{π}$ electron system migrate to the other end of the $\text{π}$ electron system. The number of $\text{σ}$ and $\text{π}$ bonds remains unchanged during this process. The number of electrons involved is counted on the basis of twice the number of curved arrow required to write the complete pericyclic reaction. In this reaction, three arrows are required. Therefore, a total of six electrons is involved in this reaction. The curved arrow mechanism for the given reaction is shown below.

Figure 4

Conclusion

The curved arrow mechanism for the reaction is shown in Figure 4. The reaction is a type of sigmatropic reaction. Along with it, the number of electrons involved in this reaction is six.

Interpretation Introduction

(e)

Interpretation:

The curved arrow mechanism for the reaction is to be stated and the reaction is to be classified as electrocyclic, cycloaddition, and the sigmatropic reaction. Along with that the number of electrons involved in the reaction is to be stated.

Concept introduction:

In the pericyclic reactions, the bond formation and dissociation occur simultaneously. The pericyclic reaction occurs in a concerted fashion with the cyclic shift of electrons. They are of three types electrocyclic, cycloaddition and the sigmatropic reactions. They occur in the presence of heat or light.

Answer to Problem 28.1P

The given reaction is an example of a retro-electrocyclic pericyclic reaction. The number of electrons involved in this reaction is two. The curved arrow mechanism is shown below.

Explanation of Solution

The given reaction is an example of a retro-electrocyclic reaction. This is because of in the electrocyclic reaction there is an intramolecular $\text{π}$ electron reaction takes place which leads to the formation of a cyclic ring with the formation of one sigma bond with the loss of one $\text{π}$ bond. In this reaction, the reverse of electrocyclic reaction takes places which is known as a retro-electrocyclic reaction. The number of electrons involved is counted on the basis of twice the number of curved arrow required to write the complete pericyclic reaction. In this reaction, one arrow is required. Therefore, a total of two electrons is involved in this reaction. The curved arrow mechanism for the given reaction is shown below.

Figure 5

Conclusion

The curved arrow mechanism for the reaction is shown in Figure 5. The reaction is a type of retro-electrocyclic reaction. Along with it, the number of electrons involved in this reaction is two.