Delocalized vs Localized Electrons - pKa, Acidity, Conjugate Base, Resonance Contributors

TL;DR

Acetic acid is more acidic than ethanol due to its lower pKa value and the stability of its conjugate base, acetate ion.

Transcript

now let's consider two molecules ethanol ch3 ch2 oh and also acetic acid ch3c and it has a carb a carboxylic acid functional group so it looks like this which of these two molecules do you believe is more acidic ethanol on the left or acidic acid on the right which one would you select it turns out that acetic acid is more acidic plus you have the ... Read More

Key Insights

• 😘 Acetic acid is more acidic than ethanol due to its lower pKa value.
• ⚾ The conjugate base of acetic acid, acetate ion, is a stronger base than the conjugate base of ethanol, ethoxide ion.
• ⚾ The stability of the conjugate base is determined by the inductive effect and resonance.
• 😑 Acetate ion is more stable and weaker as a base than ethoxide ion.
• 💪 An acid is stronger when its conjugate base is more stable or weaker.
• 😑 The inductive effect of a carbonyl group in acetic acid weakens the negative charge on the oxygen of acetate ion.
• 😑 Resonance in acetate ion allows for delocalization of the negative charge, further stabilizing the conjugate base.

Questions & Answers

Q: Why is acetic acid more acidic than ethanol?

Acetic acid is more acidic due to its lower pKa value, indicating a stronger acid. Additionally, its conjugate base, acetate ion, is more stable and weaker as a base compared to the conjugate base of ethanol, ethoxide ion.

Q: What factors contribute to the stability of the acetate ion?

The acetate ion is more stable due to the inductive effect of a carbonyl group, which withdraws electron density, weakening the negative charge on the oxygen. Additionally, resonance allows for delocalization of the negative charge, further stabilizing the conjugate base.

Q: How can resonance structures be drawn for acetate ion?

Resonance structures for acetate ion can be drawn by moving electrons between the oxygen and carbon atoms in the molecule. The resulting resonance hybrid represents the actual molecule, which is a combination of the resonance contributors.

Q: How does the stability of the conjugate base affect the acidity of an acid?

The stability of the conjugate base is inversely related to the acidity of an acid. A stronger acid has a more stable and weaker conjugate base, while a weaker acid has a relatively stronger conjugate base.

Summary & Key Takeaways

• Acetic acid is more acidic than ethanol, with pKa values of 4.76 and 15.9, respectively.

• The conjugate base of acetic acid, acetate ion, is a stronger base than the conjugate base of ethanol, ethoxide ion.

• Acetate ion is more stable and weaker as a base due to inductive effects and resonance, making acetic acid a stronger acid.