Chapter 18.5, Problem 17ATS

Interpretation Introduction

Interpretation For the given compounds, it should be determined which compound is expected to have lower ${\text{pK}}_{\text{a}}$ value

Concept introduction:

• ${\text{K}}_{\text{a}}$ is the acid dissociation constant of a solution
• ${\text{pK}}_{\text{a}}\text{=}{\text{-log}}_{\text{10}}{\text{[K}}_{\text{a}}\text{]}$
• For the stronger acids ${\text{pK}}_{\text{a}}$ value will be lower and  more stable
• For the weaker acids ${\text{pK}}_{\text{a}}$ value will be higher and less stable
• For stronger acids, its conjugate base is more stable
• For weaker acids, its conjugate base is less stable.
• Conjugate base is formed by the deprotonation of the parent acid
• Aromatic compounds are more stable than non-aromatic compound
• In order for the heterocycle to achieve a continuous system of overlapping p orbitals, the lone pair of the hetero atom must occupy a p orbital with six $\text{π}$ electrons that is four from the $\text{π}$ bonds and two from the lone pair. Then this compound is aromatic.