Concept explainers
(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
Figure 1
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.
(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
Figure 2
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.
(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
Figure 3
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.
(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
Figure 4
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.
(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
Figure 5
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.
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Chapter 28 Solutions
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