Factors that affect acidity (7)

Factors that Affect Acidity (7) - Aromaticity

Introduction

This video discusses how aromaticity, the seventh factor, affects acidity. Aromatic molecules are unusually stable, and this stability plays a significant role in determining the acidity of a molecule. The video explains that stable conjugate bases result in stronger acids.

Main Points/Arguments

• Aromaticity and Stability:

- Aromatic molecules are unusually stable.

- The stability of a conjugate base affects the acidity of the original acid.

- If a conjugate base is aromatic and stable, the conjugate acid will be more acidic.

• Comparison of Non-Aromatic and Aromatic Molecules:

- Example 1: Non-Aromatic Molecule

    - A non-aromatic molecule with a double bond that loses a proton forms a very unstable conjugate base.
    - This reaction is unfavorable, resulting in a weaker acid.

- Example 2: Aromatic Molecule

    - An aromatic molecule with two double bonds that loses a proton forms a stable conjugate base.
    - This reaction is favorable, resulting in a stronger acid.

Examples or Evidence

• Stability of Conjugate Bases:

- A non-aromatic conjugate base is highly unstable with a pKa of around 43.

- An aromatic conjugate base is unusually stable, with a pKa close to 16, making it nearly as acidic as water.

Conclusion

Aromaticity significantly stabilizes conjugate bases, making the corresponding acids stronger. Aromaticity is a crucial factor in determining acidity because it enhances the stability of the molecule. If the conjugate base of a molecule is aromatic, the conjugate acid will be unusually acidic.