List the following compounds in order of decreasing acidity:...

Name: Problem 35, Chapter 1: Organic Chemistry
Uploaded: 2021-07-05T00:01:25-08:00
Duration: 6 min 10 s
Channel: Joshua Gibson
Description: List the following compounds in order of decreasing acidity:

Key Concepts

Inductive Effects

Inductive effects involve the transmission of charge through a chain of atoms in a molecule. Electron-withdrawing groups, through inductive effects, pull electron density away from the acidic proton, thereby stabilizing the conjugate base. This stabilization increases the acidity of the compound.

Resonance Stabilization

Resonance stabilization occurs when the negative charge of the conjugate base can be delocalized over several atoms through overlapping p orbitals. This delocalization enhances the stability of the conjugate base, which in turn increases the acid strength. Resonance effects are a critical factor in comparing the relative acidities of compounds.

Conjugate Base Stability

A key factor influencing acid strength is the stability of the conjugate base that forms after deprotonation. The more stable the conjugate base, the more favorably the acid loses its proton. Stability is often enhanced by factors such as resonance delocalization or electron-withdrawing groups which can disperse or reduce the negative charge.

Acid Strength

Acid strength refers to the tendency of a substance to donate a proton in solution. It is fundamentally related to the degree to which an acid can lose a proton and how completely it ionizes. Understanding acid strength is crucial when comparing different compounds based on their ability to donate protons.

pKa Value

The pKa value is a quantitative measure of acid strength, defined as the negative logarithm of the acid dissociation constant (Ka). Lower pKa values indicate stronger acids because they signify a greater tendency for the acid to donate its proton. This numerical scale is essential for comparing the relative acidities of compounds.

Transcript

00:01 This question covers qualitatively analyzing an organic molecule to determine the acidity or basicity of the molecule.

00:11 To answer this question, we are going to be using an acronym called ario, which determines the order of each effect that each of these effects has.

00:24 They all stand for something that each of them has on determining qualitatively the acidity of a compound.

00:31 So a stands for atom.

00:31 So this is which atom is holding the acidic proton.

00:40 R stands for resonance.

00:42 Is our conjugate base stabilized through resonance? i stands for induction.

00:52 The inductive effect can be a stabilizing effect.

00:55 And it occurs when there is a highly electronegative hetero atom attached to a carbon of this on this molecule that is pulling it.

01:05 Electron density away from the acidic proton.

01:11 And lastly, it's going to be orbitals.

01:18 And each of these characteristics comes with very importance.

01:23 And it's hierarchical.

01:25 So if we are looking between two examples and they're the same, except for the acidic proton only has an n -h versus oh, then we would only look at which atom, the nitrogen versus the oxygen is the larger, more electronegative nucleus.

01:47 Now, oxygen is more electronegative and smaller than nitrogen.

01:55 So oxygen, the atom bearing the oxygen, would be the more acidic molecule.

02:07 Now, if both of them were oh, but one of them had a resident structure, another one did not have of resonant structure.

02:14 And the one with the resonant structure would have in the conjugate base.

02:18 So after you deprotonated, the conjugate base is stabilized by resonance.

02:22 And that would be the stronger acid because the base is more stable.

02:27 If all those are equal, then we would look to the inductive effect, et cetera.

02:32 So we have to rank three, sorry, four molecules...