Chapter 19, Problem 19.35P

Using the $\text{p}{K}_{\text{a}}$ table in Appendix A, determine whether each of the following bases is strong enough to deprotonate the three compounds listed below. Bases: [1] ${}^{-}\text{OH}$; [2] ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$; [3] ${}^{-}{\text{NH}}_{\text{2}}$; [4] ${\text{NH}}_{\text{3}}$; [5] $\text{HC}\equiv {\text{C}}^{-}$.

a. b. c.

Interpretation Introduction

(a)

Interpretation: The correct $\text{p}{K}_{\text{a}}$ value for the given carboxylic acid is to be identified.

Concept introduction: Carboxylic acids are the carbon compounds that contain carboxyl group as a major functional group. They are polar due to electronegativity difference between the atoms in a compound. They sometimes exist as a dimer. Dimers are the compounds that consist of two monomer units connected by bonds or forces. Carboxylic acids are synthesized from alkynes, alkene, benzene derivatives, alcohol and allylic halides by using different reagents.

Answer to Problem 19.35P

The bases that are strong enough to deprotonate the given compounds are ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$, ${}^{-}\text{OH}$, ${\text{NH}}_{\text{3}}$ and $\text{HC}\equiv {\text{C}}^{-}$.

Explanation of Solution

The given carboxylic acid is $4\text{-}$methyl benzoic acid. Its $\text{p}{K}_{\text{a}}$ value is $4.3$. It is less acidic because methyl group has positive inductive effect. It donates electrons, due to which the removal of ${\text{H}}^{+}$ ions become difficult. A base that has a higher $\text{p}{K}_{\text{a}}$ value than the $\text{p}{K}_{\text{a}}$ value of the given compound is needed to deprotonate the given compound.

The $\text{p}{K}_{\text{a}}$ value of ${}^{-}\text{OH}$, ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$, ${\text{NH}}_{\text{3}}$ and $\text{HC}\equiv {\text{C}}^{-}$ is $15.74$, $36$, $34$, $9.3$ and $25$ respectively.

Therefore, the bases that are strong enough to deprotonate the given compounds are ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$, ${}^{-}\text{OH}$, ${\text{NH}}_{\text{3}}$ and $\text{HC}\equiv {\text{C}}^{-}$.

Conclusion

The bases that are strong enough to deprotonate the given compounds are ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$, ${}^{-}\text{OH}$, ${\text{NH}}_{\text{3}}$ and $\text{HC}\equiv {\text{C}}^{-}$.

Interpretation Introduction

(b)

Interpretation: The correct $\text{p}{K}_{\text{a}}$ value for the given carboxylic acid is to be identified.

Concept introduction: Carboxylic acids are the carbon compounds that contain carboxyl group as a major functional group. They are polar due to electronegativity difference between the atoms in a compound. They sometimes exist as a dimer. Dimers are the compounds that consist of two monomer units connected by bonds or forces. Carboxylic acids are synthesized from alkynes, alkene, benzene derivatives, alcohol and allylic halides by using different reagents.

Answer to Problem 19.35P

The bases that are strong enough to deprotonate the given compounds are ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$, ${}^{-}\text{OH}$ and $\text{HC}\equiv {\text{C}}^{-}$.

Explanation of Solution

The given compound is $\text{4-}$chlorophenol. Its $\text{p}{K}_{\text{a}}$ value is $9.4$. A base which has higher $\text{p}{K}_{\text{a}}$ value than $9.4$ is needed to deprotonate the given compound.

The $\text{p}{K}_{\text{a}}$ value of ${}^{-}\text{OH}$, ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$, ${\text{NH}}_{\text{3}}$ and $\text{HC}\equiv {\text{C}}^{-}$ is $15.74$, $36$, $34$, $9.3$ and $25$ respectively.

Therefore, the bases that are strong enough to deprotonate the given compounds are ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$, ${}^{-}\text{OH}$ and $\text{HC}\equiv {\text{C}}^{-}$.

Conclusion

The bases that are strong enough to deprotonate the given compounds are ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$, ${}^{-}\text{OH}$ and $\text{HC}\equiv {\text{C}}^{-}$.

Interpretation Introduction

(c)

Interpretation: The correct $\text{p}{K}_{\text{a}}$ value for the given carboxylic acid is to be identified.

Concept introduction: Carboxylic acids are the carbon compounds that contain carboxyl group as a major functional group. They are polar due to electronegativity difference between the atoms in a compound. They sometimes exist as a dimer. Dimers are the compounds that consist of two monomer units connected by bonds or forces. Carboxylic acids are synthesized from alkynes, alkene, benzene derivatives, alcohol and allylic halides by using different reagents.

Answer to Problem 19.35P

The bases that are strong enough to deprotonate the given compounds are ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$ and $\text{HC}\equiv {\text{C}}^{-}$.

Explanation of Solution

The given carboxylic acid is $\text{2-}$methyl-propan$\text{-2-}$ol. Its $\text{p}{K}_{\text{a}}$ value is $18$. A base that has a higher $\text{p}{K}_{\text{a}}$ value than the $\text{p}{K}_{\text{a}}$ value of the given compound is needed to deprotonate the given compound.

The $\text{p}{K}_{\text{a}}$ value of ${}^{-}\text{OH}$, ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$, ${\text{NH}}_{\text{3}}$ and $\text{HC}\equiv {\text{C}}^{-}$ is $15.74$, $36$, $34$, $9.3$ and $25$ respectively.

Therefore, the bases that are strong enough to deprotonate the given compounds are ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$ and $\text{HC}\equiv {\text{C}}^{-}$.

Conclusion

The bases that are strong enough to deprotonate the given compounds are ${\text{CH}}_{\text{3}}{\text{CH}}_2{}^{-}$, ${}^{-}{\text{NH}}_{\text{2}}$ and $\text{HC}\equiv {\text{C}}^{-}$.