Chapter 26, Problem 26.26AP

Interpretation Introduction

(a)

Interpretation:

The principal organic product that is obtained when $2-$ methylthiophene reacts with acetic anhydride, ${\text{BF}}_{\text{3}}$, acid is to be stated.

Concept introduction:

The reaction in which an atom of aromatic system is replaced by an electrophile is known as electrophilic aromatic substitution reaction. The compound, acetic anhydride behaves as a acetylating compound in the presence of ${\text{BF}}_{\text{3}}$.

Answer to Problem 26.26AP

The principal organic product that is obtained when $2-$ methylthiophene reacts with acetic anhydride, ${\text{BF}}_{\text{3}}$, acid is $5-\text{acetyl}-\text{2}-\text{methylthiophene}$ as shown below.

Explanation of Solution

The reaction of $2-$ methylthiophene reacts with acetic anhydride, ${\text{BF}}_{\text{3}}$, acid is shown below.

Figure 1

In the above reaction, the second position of $2-$ methylthiophene is already captured by a methyl group, so, the fifth position in $2-$ methylthiophene is attacked by an electrophile that is para to the methyl group.

Therefore, the product formed by the above reaction is $5-\text{acetyl}-\text{2}-\text{methylthiophene}$.

Conclusion

The principal organic product, $5-\text{acetyl}-\text{2}-\text{methylthiophene}$ is obtained when $2-$ methylthiophene reacts with acetic anhydride, ${\text{BF}}_{\text{3}}$, acid.

Interpretation Introduction

(b)

Interpretation:

The principal organic product that is obtained when $2-$ methylthiophene reacts with ${\text{HNO}}_{\text{3}}$ is to be stated.

Concept introduction:

The reaction in which an atom of aromatic system is replaced by an electrophile is known as electrophilic aromatic substitution reaction. The compound, acetic anhydride behaves as a acetylating compound in the presence of ${\text{BF}}_{\text{3}}$.

Answer to Problem 26.26AP

The principal organic product that is obtained when $2-$ methylthiophene reacts with ${\text{HNO}}_{\text{3}}$ is $5-\text{acetyl}-\text{2}-\text{methylthiophene}$.

Explanation of Solution

The reaction of $2-$ methylthiophene reacts with ${\text{HNO}}_{\text{3}}$ is shown below.

Figure 2

In the above reaction, the second position of $2-$ methylthiophene is already captured\ by a methyl group, so, the fifth position in $2-$ methylthiophene is attacked by an electrophile that is para to the methyl group.

Therefore, the product formed by the above reaction is $5-\text{acetyl}-\text{2}-\text{methylthiophene}$.

Conclusion

The principal organic product, $5-\text{acetyl}-\text{2}-\text{methylthiophene}$ is obtained when $2-$ methylthiophene reacts with acetic anhydride, ${\text{BF}}_{\text{3}}$, acid.

Interpretation Introduction

(c)

Interpretation:

The incomplete reaction between diene and dienophile is to be completed with the reasonable products. The reason corresponding to the formation of the correct product is to be explained.

Concept introduction:

Diels Alder reaction is the $\left[4+2\right]$ cycloaddition reaction between a conjugated diene and a dienophile to give a cycloaddition product. It is an electrocyclic reaction in which $4\text{π}$ and $\text{2π}$ electrons of a diene and dienophile are involved respectively. The product is formed by the $\left[1,4\right]$ addition, that is, the carbons of the dienophile are attached to the first and fourth carbon of the diene.

Answer to Problem 26.26AP

The complete reaction is shown below.

Explanation of Solution

The given incomplete reaction is shown below.

Figure 3

In the above incomplete reaction, the given $s-$ trans alkene is converted to alkene. This $s-$ cis alkene behaves as a diene and undergoes Diels Alder reaction with a dienophile in the presence of heat to form an alkene as shown below.

Figure 4

Therefore, one product is obtained from the above shown Diels Alder reaction.

Conclusion

The complete reaction corresponding to the incomplete reaction between diene and dienophile is shown in Figure 4.

Interpretation Introduction

(d)

Interpretation:

The incomplete reaction between an alkene and benzoquinone is to be completed with the reasonable products. The reason corresponding to the formation of the correct product is to be explained.

Concept introduction:

Diels Alder reaction is the $\left[4+2\right]$ cycloaddition reaction between a conjugated diene and a dienophile to give a cycloaddition product. It is an electrocyclic reaction in which the $4\text{π}$ and $\text{2π}$ electrons of a diene and dienophile are involved respectively. The product is formed by the $\left[1,4\right]$ addition, that is, the carbons of the dienophile are attached to the first and fourth carbon of the diene.

Answer to Problem 26.26AP

The complete reaction is shown below.

Explanation of Solution

The given incomplete reaction is shown below.

Figure 5

In the above incomplete reaction, the given two equivalents of alkene behaves as a diene and undergoes Diels Alder reaction with benzoquinone which behaves as a dienophile in the presence of heat to form two products as shown below.

Figure 6

Therefore, two products are obtained from the above shown Diels Alder reaction. The second product is the major one because of the less van der Waals repulsion present in between two double bonds which are exocyclic.

Conclusion

The complete reaction corresponding to the incomplete reaction between diene and dienophile is shown in Figure 6.

Interpretation Introduction

(e)

Interpretation:

The incomplete reaction between a diene and a dienophile is to be completed with the reasonable products. The reason corresponding to the formation of the correct product is to be explained.

Concept introduction:

Diels Alder reaction is the $\left[4+2\right]$ cycloaddition reaction between a conjugated diene and a dienophile to give a cycloaddition product. It is an electrocyclic reaction in which the $4\text{π}$ and $\text{2π}$ electrons of a diene and dienophile are involved respectively. The product is formed by the $\left[1,4\right]$ addition, that is, the carbons of the dienophile are attached to the first and fourth carbon of the diene.

Answer to Problem 26.26AP

The complete reaction is shown below.

Explanation of Solution

The given incomplete reaction is shown below.

Figure 7

Only the $s-$ cis alkene behaves as a diene and undergoes Diels Alder reaction with a dienophile. As, the given polycyclic compound contains only one $s-$ cis alkene in the thus, only one $s-$ cis alkene behaves as a diene and undergoes Diels Alder reaction.

Figure 8

The above reaction does not form any product because the $2p$ orbital of diene and dineophile are not present in the same plane. For Diels Alder reaction, it is necessary that the $2p$ orbital of diene and dineophile should be in the same plane. In the above reaction, diene is oriented at the interior side of the ring.

Therefore, no product is formed in the above shown reaction.

Conclusion

There is no formation of the product takes place in the given reaction.

Interpretation Introduction

(f)

Interpretation:

The incomplete reaction between a diene and a dienophile is to be completed with the reasonable products. The reason corresponding to the formation of the correct product is to be explained.

Concept introduction:

Diels Alder reaction is the $\left[4+2\right]$ cycloaddition reaction between a conjugated diene and a dienophile to give a cycloaddition product. It is an electrocyclic reaction in which the $4\text{π}$ and $\text{2π}$ electrons of a diene and dienophile are involved respectively. The product is formed by the $\left[1,4\right]$ addition, that is, the carbons of the dienophile are attached to the first and fourth carbon of the diene.

Answer to Problem 26.26AP

The complete reaction is shown below.

Explanation of Solution

The given incomplete reaction is shown below.

Figure 9

In the above incomplete reaction, the intramolecular Diels Alder reaction takes place in the presence of heat to form two products as shown below.

Figure 10

In the above reaction, diene and dienophile are present in the same compound. Therefore, two products are obtained from the above shown Diels Alder reaction. Therefore, the shifting of bonds takes place within the molecule to form a single product.

Conclusion

The complete reaction corresponding to the incomplete reaction between diene and dienophile is shown in Figure 10.

Interpretation Introduction

(g)

Interpretation:

The incomplete reaction between nickel choride and $1,3-$ cyclopentadienyl anion moiety is to be completed with the reasonable products. The reason corresponding to the formation of the correct product is to be explained.

Concept introduction:

Metallocene compounds are composed of an electropositive metal ions specially transition metals like nickel or cobalt which are sandwiched between two $1,3-$ cyclopentadienyl anion. Metallocenes are the bright colored species.

Answer to Problem 26.26AP

The complete reaction is shown below.

Explanation of Solution

The given incomplete reaction is shown below.

Figure 11

In the above incomplete reaction, the nickel chloride reacts with $1,3-$ cyclopentadienyl anion moiety in the presence of sodium cation as shown below.

Figure 12

Therefore, the reaction between nickel chloride and $1,3-$ cyclopentadienyl anion moiety in the presence of sodium cation form a metallocene known as nickelocene. In this product, nickel is sandwiched between two $1,3-$ cyclopentadienyl anion.

Conclusion

The complete reaction corresponding to the incomplete reaction between nickel choride and $1,3-$ cyclopentadienyl anion moiety is shown in Figure 12.