Chapter 18, Problem 18.53AP

Interpretation Introduction

(a)

Interpretation:

The reactivity of cyclohexanol and phenol with aqueous $\text{NaOH}$ solution is to be stated.

Concept introduction:

The phenol is an aromatic compound having a formula, ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}-\text{OH}$ in which carbon has $s{p}^2$ hybridization. On the other hand, cyclohexanol is a compound having a six-member cyclic ring attached to $-\text{OH}$ group in which carbon has $s{p}^2$ hybridization. The reaction of an aqueous solution of $\text{NaOH}$ which is a stronger base with alcohol or phenol generally forms sodium salt by abstracting the acidic proton.

Answer to Problem 18.53AP

Phenol is more reactive than cyclohexanol with an aqueous $\text{NaOH}$ solution. Due to more stability of the conjugate base of phenol as compared to cyclohexanol.

Explanation of Solution

The sodium hydroxide is a strong base. It abstracts a proton from the stronger acidic compound and forms its sodium salt. In the given case, sodium hydroxide abstracts a proton from phenol and cyclohexanol and form phenoxide ion and cyclohexanol conjugate base respectively. The phenoxide ion gets stabilized by resonance structures, but this is not possible in case of cyclohexanol conjugate base. It is known that more the stability of the conjugate base more the acidity of the compound. In the given case, phenoxide ion is more stable due to this phenoxide is more acidic. Therefore, phenoxide ion is more reactive toward an aqueous $\text{NaOH}$ solution. The resonance structure of the phenoxide ion is shown below.

Figure 1

Conclusion

The reactivity of phenol is more as compared to cyclohexanol with an aqueous solution of $\text{NaOH}$. It is due to the more stability of the conjugate base of phenol.

Interpretation Introduction

(b)

Interpretation:

The reactivity of cyclohexanol and phenol with $\text{NaH}$ in $\text{THF}$ is to be stated.

Concept introduction:

The phenol is an aromatic compound having a formula, ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}-\text{OH}$ in which carbon has $s{p}^2$ hybridization. On the other hand, cyclohexanol is a compound having a six-member cyclic ring attached to $-\text{OH}$ group in which carbon has $s{p}^2$ hybridization. The reaction of an aqueous solution of $\text{NaH}$ which is a stronger base with alcohol or phenol generally forms sodium salt by abstracting the acidic proton and hydrogen gas is evolved.

Answer to Problem 18.53AP

Phenol is more reactive than cyclohexanol with an aqueous $\text{NaH}$ solution. Due to more stability of the conjugate base of phenol as compared to cyclohexanol.

Explanation of Solution

The sodium hydride is a strong base. It abstracts a proton from the stronger acidic compound and forms its sodium salt and hydrogen gas is evolved. In the given case, sodium hydroxide abstracts a proton from phenol and cyclohexanol and form phenoxide ion and cyclohexanol conjugate base respectively. The phenoxide ion gets stabilized by resonance structures, but this is not possible in case of cyclohexanol conjugate base. It is known that more the stability of the conjugate base more the acidity of the compound. In the given case, phenoxide ion is more stable due to this phenoxide is more acidic. Therefore, phenoxide ion is more reactive toward an aqueous $\text{NaH}$ solution. The resonance structure of the phenoxide ion is shown below.

Figure 2

Conclusion

The reactivity of phenol is more as compared to cyclohexanol with an aqueous solution of $\text{NaH}$. It is due to the more stability of the conjugate base of phenol.

Interpretation Introduction

(c)

Interpretation:

The reactivity of cyclohexanol and phenol with triflic anhydride in pyridine at $0°\text{C}$ is to be stated.

Concept introduction:

The triflic anhydride is a chemical compound which is also known as Trifluoromethanesulfonic anhydride. It has a molecular formula ${\left({\text{CF}}_{\text{3}}{\text{SO}}_{\text{2}}\right)}_{\text{2}}\text{O}$. It acts as a strong electrophile. It is derived from strong acid that is triflic acid. It reacts readily with nucleophiles.

Answer to Problem 18.53AP

The presence of the more nucleophilic character of cyclohexanol makes it more reactive towards triflic anhydride in pyridine at $0°\text{C}$ as compared to phenol.

Explanation of Solution

In the given case, when triflic acid reacts with cyclohexanol and phenol in the presence of pyridine at $0°\text{C}$, it forms an ester as a product. The electron density of cyclohexanol is more due to the presence of $+\text{I}$ effect of carbon which makes it better nucleophile. It is due to the participation of oxygen lone pair of electrons in resonance structure which decreases its nucleophilic activity. Therefore, triflic acid reacts easily with cyclohexanol in the presence of pyridine at $0°\text{C}$. The resonance structure of phenol is shown below.

Figure 3

Conclusion

The reactivity of cyclohexanol is more as compared to phenol with triflic acid in pyridine at $0°\text{C}$. It is due to the more nucleophilic character of cyclohexanol.

Interpretation Introduction

(d)

Interpretation:

The reactivity of cyclohexanol and phenol with concentrated aqueous $\text{HBr}$, ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ in presence of catalyst is to be stated.

Concept introduction:

The phenol is an aromatic compound having a formula, ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}-\text{OH}$ in which carbon has $s{p}^2$ hybridization. On the other hand, cyclohexanol is a compound having a six-member cyclic ring attached to $-\text{OH}$ group in which carbon has $s{p}^2$ hybridization. The saturated compound undergoes addition reaction whereas aromatic compound undergoes substitution reaction.

Answer to Problem 18.53AP

The deactivation of the aromatic ring of phenol makes it less reactive toward concentrated aqueous $\text{HBr}$, ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$, catalyst.

Explanation of Solution

Cyclohexanol is more nucleophilic as compared to phenol. It is due to the participation of the lone pair of electrons on oxygen in resonance structures of phenol. Therefore, in the given conditions cyclohexanol reacts more rapidly as compared to phenol. When cyclohexanol undergoes protonation in the presence of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ and catalyst followed by $\text{β}$-elimination, it results in the formation of cyclohexene. It further undergoes an addition reaction with $\text{HBr}$ which results in the formation of bromocyclohexane. The reaction is shown below.

Figure 4

In the case of phenol, it undergoes electrophilic aromatic substitution reaction with $\text{HBr}$, but the reaction rate is slower as compared to cyclohexanol. It is due to protonation of the hydroxyl group of phenol which deactivates the aromatic ring toward electrophilic substitution. The generation of bromide ion also becomes difficult due to the presence of strong acid ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$. Therefore, cyclohexanol is more reactive toward concentrated aqueous $\text{HBr}$ . ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$, catalyst.

Conclusion

The reactivity of phenol is less with concentrated aqueous $\text{HBr}$, ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ and catalyst. Due to protonation of the hydroxyl group of phenol which deactivates the aromatic ring toward electrophilic substitution.

Interpretation Introduction

(e)

Interpretation:

The reactivity of cyclohexanol and phenol with ${\text{Br}}_{\text{2}}$ in ${\text{CCl}}_{\text{4}}$ . dark is to be stated.

Concept introduction:

The phenol is an aromatic compound having a formula, ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}-\text{OH}$ in which carbon has $s{p}^2$ hybridization. On the other hand, cyclohexanol is a compound having a six-member cyclic ring attached to $-\text{OH}$ group in which carbon has $s{p}^2$ hybridization. The saturated compound undergoes addition reaction whereas aromatic compound undergoes substitution reaction.

Answer to Problem 18.53AP

The phenol is more reactive toward ${\text{Br}}_{\text{2}}$ in ${\text{CCl}}_{\text{4}}$, dark because it is an aromatic compound which undergoes electrophilic substitution reaction.

Explanation of Solution

The phenol is an aromatic compound which shows similar reactions as aromatic compounds show. The reaction of ${\text{Br}}_{\text{2}}$ in ${\text{CCl}}_{\text{4}}$, dark generates bromine electrophile which undergoes electrophilic substitution reaction and gives ortho- and para-substituted products. The reaction of phenol with ${\text{Br}}_{\text{2}}$ in ${\text{CCl}}_{\text{4}}$, dark is shown below.

Figure 5

Whereas no such reaction is possible with cyclohexanol because this compound gives addition reaction.

Conclusion

The phenol is an aromatic compound which undergoes electrophilic substitution reaction. Due to this, it is more reactive toward ${\text{Br}}_{\text{2}}$ in ${\text{CCl}}_{\text{4}}$, dark.

Interpretation Introduction

(f)

Interpretation:

The reactivity of cyclohexanol and phenol with ${\text{Na}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}$, in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ is to be stated.

Concept introduction:

Oxidation is defined as the addition of oxygen atom or removal of the hydrogen atom. The oxidizing agent is the substance that causes oxidation and itself get reduced. The reagent ${\text{Na}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}$, in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ acts as a strong acidic oxidizing agent. Phenol on oxidation gives different products as expected from alcohols like cyclohexanol.

Answer to Problem 18.53AP

The phenol is an aromatic compound which loses its aromatic character on reaction with ${\text{Na}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}$, in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ that is why it is less reactive as compared to cyclohexanol.

Explanation of Solution

In the given conditions, both the given compounds undergo an oxidation reaction. The reaction of cyclohexanol with ${\text{Na}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}$, in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ gives cyclohexanone. The reaction is shown below.

Figure 6

The reaction of phenol with ${\text{Na}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}$, in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ result in the formation of $p-\text{quinone}$. The reaction is shown below.

Figure 7

When phenol undergoes oxidation reaction, it loses its aromatic character which means it loses its stability. Therefore, cyclohexanol is more reactive toward ${\text{Na}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}$, in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$.

Conclusion

The phenol on reaction with ${\text{Na}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}$, in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ loses its aromatic character which decreases its reactivity towards ${\text{Na}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}$, in ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$.

Interpretation Introduction

(g)

Interpretation:

The reactivity of cyclohexanol and phenol with ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$, heat is to be stated.

Concept introduction:

The phenol is an aromatic compound having a formula, ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}-\text{OH}$ in which carbon has $s{p}^2$ hybridization. On the other hand, cyclohexanol is a compound having a six-member cyclic ring attached to $-\text{OH}$ group in which carbon has $s{p}^2$ hybridization.

Answer to Problem 18.53AP

The deactivation of the aromatic ring of phenol due to protonation of the hydroxyl group makes it less reactive toward ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$, heat.

Explanation of Solution

Cyclohexanol is more nucleophilic as compared to phenol. It is due to the participation of the lone pair of electrons on oxygen in resonance structures of phenol. Therefore, in the given conditions cyclohexanol reacts more rapidly as compared to phenol. When cyclohexanol undergoes protonation in the presence of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$, catalyst followed by $\text{β}$ elimination, it results in the formation of cyclohexene. The reaction is shown below.

Figure 8

The less nucleophilic character makes phenol less reactive toward ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$, heat.

Conclusion

The reactivity of phenol is less with ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$, heat. Due to protonation of the hydroxyl group of phenol which deactivates the aromatic ring.