Chapter 17, Problem 39PP

Interpretation Introduction

Interpretation: Reason for why there is a vast difference in ${\text{pK}}_{\text{a}}$ value of cyclopentadiene and cycloheptatriene has to be explained.

Concept Introduction:

Acid dissociation constant ${\text{K}}_{\text{a}}$ represents how strong the acid is in a solution.

  $p{K}_a=-\log K_a$

The strength of acid decreases as the value of $p{K}_a$ increases and stability decreases.

For stronger acids, its conjugate base is more stable whereas for weaker acids, its conjugate base is less stable

Aromatic compounds are more stable than non-aromatic compound

The conditions for aromatic compound are,

• It should be cyclic
• It should be planar (all atoms in the same plane)
• It must obey the Huckel’s rule (have $\text{(4}n+2\text{π)}$ electrons.)
• It must be conjugated $\text{π}$ system(all carbon should be in ${\text{sp}}^{\text{2}}$ hybridized state)