Chapter 16.SE, Problem 77AP

Interpretation Introduction

a)

Interpretation:

The product of the reaction in which actophenone reacts with HNO₃ and H₂SO₄ is to be predicted. The observed regiochemistry is to be explained by drawing the resonance structures of the intermediates.

Concept introduction:

The carbonyl group is an electron withdrawing group. Hence in aromatic electrophilic substitution reactions, the keto group will deactivate the ring and orient the electrophile to the meta position.

To predict:

The product of the reaction in which actophenone reacts with HNO₃ and H₂SO₄.

To explain:

The observed regiochemistry by drawing the resonance structures of the intermediates.

Answer to Problem 77AP

Actophenone reacts with HNO₃ and H₂SO₄ to produce m-nitroacetophenone.

Explanation of Solution

The electrophile, NO₂⁺, attacks the aromatic ring in the first step to produce a resonance stabilized carbocation (sigma complex). In the second step the carbocation deprotonates to yield the product. For the meta attack the intermediate is more stabilized as shown.

For ortho and para attack one of the resonance forms will be unstable as there will be a positive charge on the carbon to which the carbonyl group is attached.

Conclusion

Actophenone reacts with HNO₃ and H₂SO₄ to produce m-nitroacetophenone.

Interpretation Introduction

b)

Interpretation:

The product of the reaction in which toluene reacts with isopropyl chloride in the presence of AlCl₃ is to be predicted. The observed regiochemistry is to be explained by drawing the resonance structures of the intermediates.

Concept introduction:

Alkyl groups are an electron releasing groups. Hence during aromatic electrophilic substitution reactions the alkyl groups will activate the ring and orient the electrophile to the ortho and para positions.

To predict:

The product of the reaction in which toluene reacts with isopropyl chloride in the presence of AlCl₃.

To explain:

The observed regiochemistry by drawing the resonance structures of the intermediates.

Answer to Problem 77AP

When toluene reacts with isopropyl chloride in the presence of AlCl₃ the products obtained are o- and p-isopropylbenzenes. The p-isomer will predominate.

Explanation of Solution

The electrophile, (CH₃)₂CH⁺, attacks the aromatic ring in the first step to produce a resonance stabilized carbocation (sigma complex). In the second step the carbocation deprotonates to yield the product. For the ortho and para attacks, one of the the resonance structures has a positive charge on a carbon adjacent to the methyl group. This form is stabilized by electron release from the methyl group. Such stabilization is not possible for the meta attack. Hence a mixture of ortho-para products is produced in which the p-isomer predominates.

For ortho attack:

For para attack:

Conclusion

When toluene reacts with isopropyl chloride in the presence of AlCl₃ the products obtained are o- and p-isopropylbenzenes. The p-isomer will predominate.

Interpretation Introduction

c)

Interpretation:

The product of the reaction in which benzonitrile reacts with chlorine in the presence of FeCl₃ is to be predicted. The observed regiochemistry is to be explained by drawing the resonance structures of the intermediates.

Concept introduction:

The nitrile group is an electron withdrawing group. Hence in aromatic electrophilic substitution reactions the nitrile group will deactivate the ring and orient the electrophile to the meta position.

To predict:

The product of the reaction in which benzonitrile reacts with chlorine in the presence of FeCl₃.

To explain:

The observed regiochemistry by drawing the resonance structures of the intermediates.

Answer to Problem 77AP

When benzonitrile reacts with chlorine in the presence of FeCl₃ meta chlorobenzonitrile will be produced.

Explanation of Solution

The electrophile, Cl⁺, attacks the aromatic ring in the first step to produce a resonance stabilized carbocation (sigma complex). In the second step the carbocation deprotonates to yield the product. For the meta attack the intermediate is more stabilized as shown.

For ortho and para attack one of the resonance forms will be unstable as there will be a positive charge on the carbon to which the nitrile group is attached.

Conclusion

When benzonitrile reacts with chlorine in the presence of FeCl₃ meta chlorobenzonitrile will be produced.

Interpretation Introduction

d)

Interpretation:

The product of the reaction in which methoxy benzene reacts with iodine in the presence of CuCl₂ is to be predicted. The observed regiochemistry is to be explained by drawing the resonance structures of the intermediates.

Concept introduction:

Methoxy group is an electron releasing group. Hence during aromatic electrophilic substitution reactions the methoxy group will activate the ring and orient the electrophile to the ortho and para positions.

To predict:

The product of the reaction in which benzene reacts with iodine in the presence of CuCl₂.

To explain:

The observed regiochemistry by drawing the resonance structures of the intermediates.

Answer to Problem 77AP

When methoxybenzene reacts with iodine in the presence of CuCl₂, the products obtained are o- and p-iodobenzenes.

Explanation of Solution

Iodine itself is unreactive toward aromatic rings. CuCl₂ accelerate the iodination reaction by oxidizing iodine to a more powerful by electrophilic species that reacts like I⁺.

The electrophile, I⁺, attacks the aromatic ring in the first step to produce a resonance stabilized carbocation (sigma complex). In the second step the carbocation deprotonates to yield the product. For the ortho and para attacks, one of the the resonance structures has a positive charge on a carbon adjacent to the methoxy group. This form is stabilized by electron release from the methoxy group. Such stabilization is not possible for the meta attack. Hence a mixture of ortho-para products is produced.

Ortho attack:

Meta attack:

Conclusion

When methoxybenzene reacts with iodine in the presence of CuCl₂, the products obtained are o- and p-iodobenzenes.