Chapter 4, Problem 4.38AP

(a)

Interpretation Introduction

Interpretation:

The most acidic hydrogen in given molecule has to be labelled and justify it using ${\text{pK}}_{\text{a}}$ values of it.

Concept Introduction:

Position of equilibrium in acid-base reaction:

In an acid-base reaction, the position of equilibrium always favors reaction of the stronger acid and stronger base to form the weaker acid and weaker base. Therefore, the major species present at equilibrium in an acid-base reaction are weaker acid and weaker base.  The reaction equilibrium shifts to a direction where weaker acid and weaker base is formed.  Acids with greater ${\text{pK}}_{\text{a}}$ values are weak acids and base with greater ${\text{pK}}_{\text{b}}$ values are weaker base.

Explanation of Solution

Given molecule,

    ${\text{HOCH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{NH}}_{\text{2}}$

Increase in ${\text{pK}}_{\text{a}}$ value decreases ${\text{K}}_{\text{a}}$ value, which determines acidity of a compound.  Therefore, hydrogen with lower ${\text{pK}}_{\text{a}}$ value has higher ${\text{K}}_{\text{a}}$ value and more acidic.  In given compound, hydrogen attached to oxygen has less ${\text{pK}}_{\text{a}}$ value than hydrogen bonded to nitrogen.  The most acidic hydrogen atom is labelled as,

    $\begin{array}{l}H{\text{OCH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{NH}}_{\text{2}}\\ {\text{pK}}_{\text{a}}\text{~16}\text{~38}\end{array}$

(b)

Interpretation Introduction

Interpretation:

The most acidic hydrogen in given molecule has to be labelled and justify it using ${\text{pK}}_{\text{a}}$ values of it.

Concept Introduction:

Position of equilibrium in acid-base reaction:

In an acid-base reaction, the position of equilibrium always favors reaction of the stronger acid and stronger base to form the weaker acid and weaker base. Therefore, the major species present at equilibrium in an acid-base reaction are weaker acid and weaker base.  The reaction equilibrium shifts to a direction where weaker acid and weaker base is formed.  Acids with greater ${\text{pK}}_{\text{a}}$ values are weak acids and base with greater ${\text{pK}}_{\text{b}}$ values are weaker base.

Explanation of Solution

Given molecule,

    ${\text{HSCH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{NH}}_{\text{2}}$

Increase in ${\text{pK}}_{\text{a}}$ value decreases ${\text{K}}_{\text{a}}$ value, which determines acidity of a compound.  Therefore, hydrogen with lower ${\text{pK}}_{\text{a}}$ value has higher ${\text{K}}_{\text{a}}$ value and more acidic.  In given compound, hydrogen attached to sulfur has less ${\text{pK}}_{\text{a}}$ value than hydrogen bonded to nitrogen.  The most acidic hydrogen atom is labelled as,

    $\begin{array}{l}H{\text{SCH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{NH}}_{\text{2}}\\ {\text{pK}}_{\text{a}}\text{~7}\text{~38}\end{array}$

(c)

Interpretation Introduction

Interpretation:

The most acidic hydrogen in given molecule has to be labelled and justify it using ${\text{pK}}_{\text{a}}$ values of it.

Concept Introduction:

Position of equilibrium in acid-base reaction:

In an acid-base reaction, the position of equilibrium always favors reaction of the stronger acid and stronger base to form the weaker acid and weaker base. Therefore, the major species present at equilibrium in an acid-base reaction are weaker acid and weaker base.  The reaction equilibrium shifts to a direction where weaker acid and weaker base is formed.  Acids with greater ${\text{pK}}_{\text{a}}$ values are weak acids and base with greater ${\text{pK}}_{\text{b}}$ values are weaker base.

Explanation of Solution

Given molecule,

    ${\text{HOCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{C}\equiv \text{CH}$

Increase in ${\text{pK}}_{\text{a}}$ value decreases ${\text{K}}_{\text{a}}$ value, which determines acidity of a compound.  Therefore, hydrogen with lower ${\text{pK}}_{\text{a}}$ value has higher ${\text{K}}_{\text{a}}$ value and more acidic.  In given compound, hydrogen attached to oxygen has less ${\text{pK}}_{\text{a}}$ value than hydrogen bonded to terminal carbon.  The most acidic hydrogen atom is labelled as,

    $\begin{array}{l}H{\text{OCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{C}\equiv \text{CH}\\ {\text{pK}}_{\text{a}}\text{~16}\text{~25}\end{array}$

(d)

Interpretation Introduction

Interpretation:

The most acidic hydrogen in given molecule has to be labelled and justify it using ${\text{pK}}_{\text{a}}$ values of it.

Concept Introduction:

Position of equilibrium in acid-base reaction:

In an acid-base reaction, the position of equilibrium always favors reaction of the stronger acid and stronger base to form the weaker acid and weaker base. Therefore, the major species present at equilibrium in an acid-base reaction are weaker acid and weaker base.  The reaction equilibrium shifts to a direction where weaker acid and weaker base is formed.  Acids with greater ${\text{pK}}_{\text{a}}$ values are weak acids and base with greater ${\text{pK}}_{\text{b}}$ values are weaker base.

Explanation of Solution

Given molecule,

    ${\text{HOCOCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{SH}$

Increase in ${\text{pK}}_{\text{a}}$ value decreases ${\text{K}}_{\text{a}}$ value, which determines acidity of a compound.  Therefore, hydrogen with lower ${\text{pK}}_{\text{a}}$ value has higher ${\text{K}}_{\text{a}}$ value and more acidic.  In given compound, hydrogen attached to oxygen has less ${\text{pK}}_{\text{a}}$ value than hydrogen bonded to sulfur.  The most acidic hydrogen atom is labelled as,

    $\begin{array}{l}H{\text{OCOCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{SH}\\ {\text{pK}}_{\text{a}}\text{~4}\text{.5}\text{~7}\end{array}$

(e)

Interpretation Introduction

Interpretation:

The most acidic hydrogen in given molecule has to be labelled and justify it using ${\text{pK}}_{\text{a}}$ values of it.

Concept Introduction:

Position of equilibrium in acid-base reaction:

In an acid-base reaction, the position of equilibrium always favors reaction of the stronger acid and stronger base to form the weaker acid and weaker base. Therefore, the major species present at equilibrium in an acid-base reaction are weaker acid and weaker base.  The reaction equilibrium shifts to a direction where weaker acid and weaker base is formed.  Acids with greater ${\text{pK}}_{\text{a}}$ values are weak acids and base with greater ${\text{pK}}_{\text{b}}$ values are weaker base.

Explanation of Solution

Given molecule,

    

Increase in ${\text{pK}}_{\text{a}}$ value decreases ${\text{K}}_{\text{a}}$ value, which determines acidity of a compound.  Therefore, hydrogen with lower ${\text{pK}}_{\text{a}}$ value has higher ${\text{K}}_{\text{a}}$ value and more acidic.  In given compound, hydrogen attached to carboxylic acid oxygen has less ${\text{pK}}_{\text{a}}$ value than hydrogen bonded to oxygen of alcohol.  The most acidic hydrogen atom is labelled as,

    

(f)

Interpretation Introduction

Interpretation:

The most acidic hydrogen in given molecule has to be labelled and justify it using ${\text{pK}}_{\text{a}}$ values of it.

Concept Introduction:

Position of equilibrium in acid-base reaction:

In an acid-base reaction, the position of equilibrium always favors reaction of the stronger acid and stronger base to form the weaker acid and weaker base. Therefore, the major species present at equilibrium in an acid-base reaction are weaker acid and weaker base.  The reaction equilibrium shifts to a direction where weaker acid and weaker base is formed.  Acids with greater ${\text{pK}}_{\text{a}}$ values are weak acids and base with greater ${\text{pK}}_{\text{b}}$ values are weaker base.

Explanation of Solution

Given molecule,

    ${\text{H}}_{\text{3}}{\text{N}}^{\text{+}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{COOH}$

Increase in ${\text{pK}}_{\text{a}}$ value decreases ${\text{K}}_{\text{a}}$ value, which determines acidity of a compound.  Therefore, hydrogen with lower ${\text{pK}}_{\text{a}}$ value has higher ${\text{K}}_{\text{a}}$ value and more acidic.  In given compound, hydrogen attached to oxygen has less ${\text{pK}}_{\text{a}}$ value than hydrogen bonded to nitrogen.  The most acidic hydrogen atom is labelled as,

    $\begin{array}{l}{\text{H}}_{\text{3}}{\text{N}}^{\text{+}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{COO}H\\ {\text{pK}}_{\text{a}}\text{~9}\text{~4}\text{.5}\end{array}$

(g)

Interpretation Introduction

Interpretation:

The most acidic hydrogen in given molecule has to be labelled and justify it using ${\text{pK}}_{\text{a}}$ values of it.

Concept Introduction:

Position of equilibrium in acid-base reaction:

In an acid-base reaction, the position of equilibrium always favors reaction of the stronger acid and stronger base to form the weaker acid and weaker base. Therefore, the major species present at equilibrium in an acid-base reaction are weaker acid and weaker base.  The reaction equilibrium shifts to a direction where weaker acid and weaker base is formed.  Acids with greater ${\text{pK}}_{\text{a}}$ values are weak acids and base with greater ${\text{pK}}_{\text{b}}$ values are weaker base.

Explanation of Solution

Given molecule,

    ${\text{H}}_{\text{3}}{\text{N}}^{\text{+}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{COO}}^{\text{-}}$

Increase in ${\text{pK}}_{\text{a}}$ value decreases ${\text{K}}_{\text{a}}$ value, which determines acidity of a compound.  Therefore, hydrogen with lower ${\text{pK}}_{\text{a}}$ value has higher ${\text{K}}_{\text{a}}$ value and more acidic.  In given compound, hydrogen attached to nitrogen is the only acidic hydrogen and labelled as,

    $\begin{array}{l}{H}_{\text{3}}{\text{N}}^{\text{+}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{COO}}^{\text{-}}\\ {\text{pK}}_{\text{a}}\text{~9}\end{array}$

(h)

Interpretation Introduction

Interpretation:

The most acidic hydrogen in given molecule has to be labelled and justify it using ${\text{pK}}_{\text{a}}$ values of it.

Concept Introduction:

Position of equilibrium in acid-base reaction:

In an acid-base reaction, the position of equilibrium always favors reaction of the stronger acid and stronger base to form the weaker acid and weaker base. Therefore, the major species present at equilibrium in an acid-base reaction are weaker acid and weaker base.  The reaction equilibrium shifts to a direction where weaker acid and weaker base is formed.  Acids with greater ${\text{pK}}_{\text{a}}$ values are weak acids and base with greater ${\text{pK}}_{\text{b}}$ values are weaker base.

Explanation of Solution

Given molecule,

    ${\text{HSCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$

Increase in ${\text{pK}}_{\text{a}}$ value decreases ${\text{K}}_{\text{a}}$ value, which determines acidity of a compound.  Therefore, hydrogen with lower ${\text{pK}}_{\text{a}}$ value has higher ${\text{K}}_{\text{a}}$ value and more acidic.  In given compound, hydrogen attached to sulfur has less ${\text{pK}}_{\text{a}}$ value than hydrogen bonded to oxygen.  The most acidic hydrogen atom is labelled as,

    $\begin{array}{l}H{\text{SCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}\\ {\text{pK}}_{\text{a}}\text{~7}\text{~16}\end{array}$