Chapter 3, Problem 3.47AP

Interpretation Introduction

(a)

Interpretation:

An explanation regarding the arrangement of the compounds in order of their decreasing $\text{p}{K}_{\text{a}}$ is to be stated.

Concept introduction:

The $\text{p}{K}_{\text{a}}$ value of an acid is the negative logarithm of ${\text{K}}_{\text{a}}$ (acid dissociation constant). It indicates the acidity of a compound. The acidity of a compound increases as a result $\text{p}{K}_{\text{a}}$ value decreases.

Answer to Problem 3.47AP

The arrangement of the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown below.

$\begin{array}{l}{\text{CH}}_{\text{3}}{\text{CH}}_2\text{OH}{\text{ClCH}}_2{\text{CH}}_2\text{OH}{\text{Cl}}_2{\text{CHCH}}_2\text{OH}\\ \text{A}>\text{C}>\text{B}\end{array}$

Explanation of Solution

The given compounds are shown below.

$\begin{array}{l}{\text{CH}}_{\text{3}}{\text{CH}}_2\text{OH}{\text{Cl}}_2{\text{CHCH}}_2\text{OH}{\text{ClCH}}_2{\text{CH}}_2\text{OH}\\ \text{A}\text{B}\text{C}\end{array}$

Figure 1

Compounds shown in Figure 1 are alcohols that mean acidic proton is bonded to oxygen.

Compound B contains two chlorine atoms which are electron-withdrawing group. Due to $-\text{I}$ effect of two chlorine atoms, the acidity of compound B increases. Therefore, the acidity of compound B is more than compound A and compound C.

Compound C contains only one chlorine atom which is an electron-withdrawing group Due to $-\text{I}$ effect of a chlorine atom, the acidity of compound C increases. Compound C contains only one chlorine atom due to which the acidity of compound C is more than compound A.

Compound A contains one methyl group which is an electron-donating group. Due to $\text{+I}$ effect of the methyl group, the acidity of compound A decreases.

Therefore, the order of acidity of the compounds is shown below.

$\begin{array}{l}{\text{CH}}_{\text{3}}{\text{CH}}_2\text{OH}{\text{ClCH}}_2{\text{CH}}_2\text{OH}{\text{Cl}}_2{\text{CHCH}}_2\text{OH}\\ \text{A}<\text{C}<\text{B}\end{array}$

Figure 2

The $\text{p}{K}_{\text{a}}$ value of an acid is the negative logarithm of ${\text{K}}_{\text{a}}$ (acid dissociation constant). The, on increasing acidity, $\text{p}{K}_{\text{a}}$ value decreases.

Therefore, the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown below.

$\begin{array}{l}{\text{CH}}_{\text{3}}{\text{CH}}_2\text{OH}{\text{ClCH}}_2{\text{CH}}_2\text{OH}{\text{Cl}}_2{\text{CHCH}}_2\text{OH}\\ \text{A}>\text{C}>\text{B}\end{array}$

Figure 3

The order of decreasing $p{\text{K}}_{\text{a}}$ value of the compounds is $\text{A}>\text{C}>\text{B}$.

Conclusion

The arrangement of the order of decreasing $p{\text{K}}_{\text{a}}$ value of the compounds is shown in Figure 3.

Interpretation Introduction

(b)

Interpretation:

An explanation regarding the arrangement of the compounds in order of their decreasing $\text{p}{K}_{\text{a}}$ is to be stated.

Concept introduction:

The $\text{p}{K}_{\text{a}}$ value of an acid is the negative logarithm of ${\text{K}}_{\text{a}}$ (acid dissociation constant). It indicates the acidity of a compound. The acidity of a compound increases as a result $\text{p}{K}_{\text{a}}$ value decreases.

Answer to Problem 3.47AP

The arrangement of the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown below.

$\begin{array}{l}{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{SH}{\text{ClCH}}_2{\text{CH}}_2\text{SH}\\ \text{B}>\text{C}>\text{A}\end{array}$

Explanation of Solution

The given compounds are shown below.

$\begin{array}{l}{\text{ClCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{SH}{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}{\text{CH}}_3{\text{CH}}_2\text{SH}\\ \text{A}\text{B}\text{C}\end{array}$

Figure 4

According to the elemental effect, the acidity increases as the atomic number attached to the acidic hydrogen also increases. Compound A and C contain a sulfur atom which has a high atomic number than an oxygen atom. The, $\text{S}-\text{H}$ bond is more acidic as compared to $\text{O}-\text{H}$ bond. Therefore, the acidity of compound B is less than compound C and A.

Compound A contains only chlorine atom which is an electron-withdrawing group. Due to $-\text{I}$ effect of a chlorine atom, the acidity of compound A increases.

Compound C contains ${\text{CH}}_{\text{3}}$ group which is an electron-donating group. Due to $+\text{I}$ effect of ${\text{CH}}_{\text{3}}$ group the acidity of compound C decreases. The, acidity of compound C is less than compound A.

Therefore, the order of acidity of the compounds is shown below.

$\begin{array}{l}{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{SH}{\text{ClCH}}_2{\text{CH}}_2\text{SH}\\ \text{B}<\text{C}<\text{A}\end{array}$

Figure 5

The $\text{p}{K}_{\text{a}}$ value of an acid is the negative logarithm of ${\text{K}}_{\text{a}}$ (acid dissociation constant). The, on increasing acidity, $\text{p}{K}_{\text{a}}$ value decreases.

Therefore, the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown below.

$\begin{array}{l}{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH}{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{SH}{\text{ClCH}}_2{\text{CH}}_2\text{SH}\\ \text{B}>\text{C}>\text{A}\end{array}$

Figure 6

The order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is $\text{B}>\text{C}>\text{A}$.

Conclusion

The arrangement of the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown in Figure 6.

Interpretation Introduction

(c)

Interpretation:

An explanation regarding the arrangement of the compounds in order of their decreasing $\text{p}{K}_{\text{a}}$ is to be stated.

Concept introduction:

The $p{\text{K}}_{\text{a}}$ value of an acid is the negative logarithm of ${\text{K}}_{\text{a}}$ (acid dissociation constant). It indicates the acidity of a compound. The acidity of a compound increases as a result $\text{p}{K}_{\text{a}}$ value decreases.

Answer to Problem 3.47AP

The arrangement of the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown below.

Explanation of Solution

The given compounds are shown below.

Figure 7

According to the elemental effect, the acidity increases as the atomic number attached to the acidic hydrogen also increases. The element $\left(\text{As}\right)$ present in compound A and B. The element present in compound C and D is $\text{N}$ and $\text{H}$ respectively.

The atomic number of arsenic is higher than nitrogen and phosphorus. The $\text{As}-\text{H}$ bond is more acidic than $\text{N}-\text{H}$ and $\text{P}-\text{H}$ bond. Therefore, compound A and B is more acidic than compound C and D.

The atomic number of phosphorus is higher than nitrogen. The $\text{P}-\text{H}$ bond is more acidic than $\text{N}-\text{H}$ bond. Therefore, compound D is more acidic than compound C.

According to the charge effect, the acidity increases with the presence of positive charge on atom attached to acidic hydrogen. Compound B contains a positive charge. Therefore, compound B is more acidic than compound A.

Therefore, the order of acidity of the compounds is shown below.

Figure 8

The $\text{p}{K}_{\text{a}}$ value of an acid is the negative logarithm of ${\text{K}}_{\text{a}}$ (acid dissociation constant). The, on increasing acidity, $\text{p}{K}_{\text{a}}$ value decreases.

Therefore, the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown below.

Figure 9

The order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is $\text{C}>\text{D}>\text{A}>\text{B}$.

Conclusion

The arrangement of the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown in Figure 9.

Interpretation Introduction

(d)

Interpretation:

An explanation regarding the arrangement of the compounds in order of their decreasing $\text{p}{K}_{\text{a}}$ is to be stated.

Concept introduction:

The $\text{p}{K}_{\text{a}}$ value of an acid is the negative logarithm of ${\text{K}}_{\text{a}}$ (acid dissociation constant). It indicates the acidity of a compound. The acidity of a compound increases as a result $\text{p}{K}_{\text{a}}$ value decreases.

Answer to Problem 3.47AP

The arrangement of the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown below.

Explanation of Solution

The given compounds are shown below.

Figure 10

According to the charge effect, the acidity increases with the presence of positive charge on atom attached to acidic hydrogen. Compound C contains a positive charge. Therefore, compound C is more acidic than compound A and B.

Compound B contains only $\text{N}{\left({\text{CH}}_{\text{3}}\right)}_3$ group. Due to opposite polar effect compound B is least acidic.

Therefore, the order of acidity of the compounds is shown below.

Figure 11

The $\text{p}{K}_{\text{a}}$ value of an acid is the negative logarithm of ${\text{K}}_{\text{a}}$ (acid dissociation constant). The, on increasing acidity, $\text{p}{K}_{\text{a}}$ value decreases.

Therefore, the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown below.

Figure 12

The order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is $\text{B}>\text{A}>\text{C}$.

Conclusion

The arrangement of the order of decreasing $\text{p}{K}_{\text{a}}$ value of the compounds is shown in Figure 12.