Chapter 16, Problem 16.44AP

Interpretation Introduction

(a)

Interpretation:

The compounds mesitylene, toluene, and $\text{1, 2, 4-trimethylbenzene}$ are to be arranged in increasing order of increasing reactivity toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$.

Concept introduction:

The replacement of hydrogen atom attached to a carbon atom of electron-rich benzene ring by an electrophile is known as electrophilic aromatic substitution reaction. The rate of electrophilic aromatic substitution reaction depends on the substituted group on the aromatic ring. The ring deactivating group retards the electrophilic aromatic substitution reaction and ring activating group enhances the electrophilic aromatic substitution reaction.

Answer to Problem 16.44AP

The compounds mesitylene, toluene, and $\text{1, 2, 4-trimethylbenzene}$ are arranged in increasing order of increasing reactivity toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ as shown below.

$\text{Toluene}<\text{1, 2, 4-trimethylbenzene}<\text{mesitylene}$

Explanation of Solution

The structure of mesitylene, toluene, and $\text{1, 2, 4-trimethylbenzene}$ are shown below.

Figure 1

The reaction of any aromatic compound with ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ forms a nitro substituted product. It is a type of electrophilic aromatic substitution reaction. The reactivity of compounds toward this nitration reaction will be the same as other electrophilic aromatic substitution reaction.

The methyl group is electron-donating group. It activates the phenyl ring. The toluene has only one methyl group attached to it. Therefore, it will be least reactive towards ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$. The methyl group is ortho and para directing group. In mesitylene, all three ortho positions are vacant. In $\text{1, 2, 4-trimethylbenzene}$, the ortho position of methyl group substitute to carbon atom $\text{C1}$ is the meta position of methyl group substitute to carbon atom $\text{C4}$. Therefore, the reactivity of mesitylene towards ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is higher than that of $\text{1, 2, 4-trimethylbenzene}$.

The order of reactivity toward nitration reaction is shown below.

$\text{Toluene}<\text{1, 2, 4-trimethylbenzene}<\text{mesitylene}$

Conclusion

The increasing order of reactivity towards toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is shown below.

$\text{Toluene}<\text{1, 2, 4-trimethylbenzene}<\text{mesitylene}$

Interpretation Introduction

(b)

Interpretation:

The compounds chlorobenzene, benzene, and nitrobenzene are to be arranged in increasing order of increasing reactivity toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$.

Concept introduction:

The replacement of hydrogen atom attached to a carbon atom of electron-rich benzene ring by an electrophile is known as electrophilic aromatic substitution reaction. The rate of electrophilic aromatic substitution reaction depends on the substituted group on the aromatic ring. The ring deactivating group retards the electrophilic aromatic substitution reaction and ring activating group enhances the electrophilic aromatic substitution reaction.

Answer to Problem 16.44AP

The compounds chlorobenzene, benzene, and nitrobenzene are arranged in increasing order of increasing reactivity toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ as shown below.

$\text{Nitrobenzene}<\text{chlorobenzene}<\text{benzene}$

Explanation of Solution

The structure of chlorobenzene, benzene, and nitrobenzene are shown below.

Figure 2

The reaction of any aromatic compound with ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ forms a nitro substituted product. It is a type of electrophilic aromatic substitution reaction. The reactivity of compounds toward this nitration reaction will be same as other electrophilic aromatic substitution reaction.

The nitro and chloro groups are electron-withdrawing groups. Therefore, the reactivity of the chlorobenzene and nitrobenzene will be less than that of benzene. The nitro group is stronger deactivating group than chloro group. Therefore, the order of reactivity toward nitration reaction is shown below.

$\text{Nitrobenzene}<\text{chlorobenzene}<\text{benzene}$

Conclusion

The increasing order of reactivity towards toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is shown below.

$\text{Nitrobenzene}<\text{chlorobenzene}<\text{benzene}$

Interpretation Introduction

(c)

Interpretation:

The compounds $m\text{-}$ chloroanisole, $p\text{-}$ chloroanisole, and anisole are to be arranged in increasing order of increasing reactivity toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$.

Concept introduction:

The replacement of hydrogen atom attached to a carbon atom of electron-rich benzene ring by an electrophile is known as electrophilic aromatic substitution reaction. The rate of electrophilic aromatic substitution reaction depends on the substituted group on the aromatic ring. The ring deactivating group retards the electrophilic aromatic substitution reaction and ring activating group enhances the electrophilic aromatic substitution reaction.

Answer to Problem 16.44AP

The compounds $m\text{-}$ chloroanisole, $p\text{-}$ chloroanisole, and anisole are to be arranged in increasing order of increasing reactivity toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ as shown below.

$p\text{-chloroanisole}<m\text{-chloroanisole}<\text{anisole}$

Explanation of Solution

The structure of $m\text{-}$ chloroanisole, $p\text{-}$ chloroanisole, and anisole are shown below.

Figure 3

The reaction of any aromatic compound with ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ forms a nitro substituted product. It is a type of electrophilic aromatic substitution reaction. The reactivity of compounds toward this nitration reaction will be same as other electrophilic aromatic substitution reaction.

The methoxy group and chloro groups are ortho and para directing groups. The methoxy group is electron releasing group and chloro group is electron-withdrawing group.

Therefore, the reactivity of anisole will be highest among the rest of the compound toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$. In $m\text{-}$ chloroanisole, number of favored ortho and para positions are more than in $p\text{-}$ chloroanisole. Therefore, the reactivity of $m\text{-}$ chloroanisole nitration reaction will be higher than that of $p\text{-}$ chloroanisole.

The order of reactivity toward nitration reaction is shown below.

$p\text{-chloroanisole}<m\text{-chloroanisole}<\text{anisole}$

Conclusion

The increasing order of reactivity towards toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is shown below.

$p\text{-chloroanisole}<m\text{-chloroanisole}<\text{anisole}$

Interpretation Introduction

(d)

Interpretation:

The compounds acetophenone, $p\text{-}$ methoxyacetophenone, and $p\text{-}$ bromoacetophenone are to be arranged in increasing order of increasing reactivity toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$.

Concept introduction:

The replacement of hydrogen atom attached to a carbon atom of electron-rich benzene ring by an electrophile is known as electrophilic aromatic substitution reaction. The rate of electrophilic aromatic substitution reaction depends on the substituted group on the aromatic ring. The ring deactivating group retards the electrophilic aromatic substitution reaction and ring activating group enhances the electrophilic aromatic substitution reaction.

Answer to Problem 16.44AP

The compounds acetophenone, $p\text{-}$ methoxyacetophenone, and $p\text{-}$ bromoacetophenone are arranged in increasing order of increasing reactivity toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ as shown below.

$p\text{-bromoacetophenone}<p\text{-methoxyacetophenone}<\text{acetophenone}$

Explanation of Solution

The structure of acetophenone, $p\text{-}$ methoxyacetophenone, and $p\text{-}$ bromoacetophenone are shown below.

Figure 4

The reaction of any aromatic compound with ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ forms a nitro substituted product. It is a type of electrophilic aromatic substitution reaction. The reactivity of compounds toward this nitration reaction will be the same as other electrophilic aromatic substitution reaction.

The acetyl group and bromo group is electron-withdrawing groups and methoxy group is electron releasing group. Acetophenone has a ring activating group attached on it. Therefore, it is most reactive toward nitration reaction among the rest of the compound. The compound $p\text{-}$ methoxyacetophenone has one ring activating and one ring deactivating group on it. The compound $p\text{-}$ bromoacetophenone has ring-deactivating group on it. Therefore, the order of reactivity toward nitration reaction is shown below.

$p\text{-bromoacetophenone}<p\text{-methoxyacetophenone}<\text{acetophenone}$

Conclusion

The increasing order of reactivity towards toward ${\text{HNO}}_{\text{3}}$ in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is shown below.

$p\text{-bromoacetophenone}<p\text{-methoxyacetophenone}<\text{acetophenone}$