Chapter 17.5, Problem 12ATS

Interpretation Introduction

Interpretation For the given compounds, the vast difference in the ${\text{pK}}_{\text{a}}$ values should be explained

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.
• Aromatic compounds are more stable than non-aromatic compound
• The conditions for aromatic compound are,

1. 1. 1. It should be planar
   2. 2. It must obey the Huckel’s rule

The requirement of an odd number of electron pair is called Huckel’s rule. A     compound can only be aromatic if the number of $\text{π}$ electron in the ring is 2, 6,10,14,18 and so on. This series of number can be expressed mathematically as $\text{4n+2}$, where n should be an integer and the compound is aromatic.

1. 3. Continuous conjugated $\text{π}$ system(all carbon should be in ${\text{sp}}^{\text{2}}$ hybridized state)