Chapter 4, Problem 48CTQ

a)

Interpretation Introduction

Interpretation: Each number and the most acidic hydrogen in below molecule should be determined.

  

Concept introduction: Electronegative elements have tendency to attract electrons towards it. Since electrons are shared more towards electronegative element, it acquires partial negative charge on it. As a result, other bonded atom develops partial positive charge. Polarization in any molecule arises due to electronegativity difference between bonded atoms. Polarization that is caused by electronegative atom can induce polarization in neighboring bonds to very small extent. This effect is known as inductive effect. Due to this effect, hydrogen attached to positive atom become more acidic than that on neutral atom. This also explains more acidic nature of hydrogens attached to electronegative atoms as compared to other atoms.

b)

Interpretation Introduction

Interpretation: Whether the most acidic hydrogen in below structure is consistent with fact that this molecule has $\text{p}{K}_{\text{a}}$ close to 16 or not should be determined.

  

Concept introduction: $\text{p}{K}_a$ is defined as negative logarithm of dissociation constant of acid $\left(K_a\right)$ . If conjugate acid has high $\text{p}{K}_a$ value, its dissociation constant will be less. As a result, it cannot dissociate completely in solutions and acts as weak acid. Strength of base and its conjugate acid are inversely related to each other. So base that corresponds to weak conjugate acid will be strong base. Higher the $\text{p}{K}_a$ of conjugate acid, the stronger the base and vice-versa.