Which acid of each pair would you expect to be stronger?...

Key Concepts

Bond Strength

The bond strength between the acidic hydrogen and the rest of the molecule is crucial in determining acid strength. Weaker bonds make it easier for the acid to donate a proton, resulting in a stronger acid.

Electronegativity

Electronegativity refers to an atom’s ability to attract electrons. Atoms with higher electronegativity can stabilize a negative charge more effectively, thereby enhancing the acid's strength when these atoms are part of the conjugate base.

Inductive Effects

Inductive effects involve the transmission of charge through a chain of atoms as a result of electronegativity differences. Electron-withdrawing groups can stabilize the negative charge on the conjugate base through these effects, thereby increasing the acidity of the molecule.

Acid Strength

Acid strength is determined by an acid’s ability to donate a proton (H+). This concept includes evaluating factors such as the stability of the conjugate base, bond strength between the hydrogen and the rest of the molecule, and the extent to which the acid dissociates in solution.

Resonance Stabilization

Resonance stabilization involves the delocalization of electrons over multiple atoms in the conjugate base, which lowers its energy and increases its stability. A conjugate base that is better stabilized by resonance will result in a stronger parent acid.

Transcript

00:04 When comparing acidity of two different acids and trying to find which one is strongest, the common part to look for is a strong acid is defined by how willing it is to give up its hydrogen.

00:32 And what i mean by this is that if we were to look at the partial charges or look at where the electrons are more focused in a carboxylic acid.

00:53 I just call this r.

00:54 So this is in general.

00:59 Because of resonance, there is a lot of electrons with these dotted lines.

01:08 I will do it again in red.

01:11 There's a lot of electrons moving through here.

01:15 And if this hydrogen was removed, these two oxygens would share this negative charge.

01:27 And because of resonance, it gets stabilized.

01:32 And in order to make an acid very strong, this r group should have electron with drawing groups.

01:46 Because if electrons were pushed, that would make this carbon more partially negative, and we want it to be more partially positive.

02:00 So we want to take more electrons in terms of electron density and have a dipole that's going more that way.

02:13 Or another way to say is more like here from the carbon, not really from the oxygen, because there's already diables going that way.

02:22 So we want more electron withdrawing groups to take that density from electrons.

02:30 That way the oxygen and the carboxylic acid would be more willing to give up that hydrogen to become a base.

02:39 So that's what defines a strong acid, the willingness of it to give up that hydrogen.

02:45 So if we were to compare these two acids on the left, this first one has a carbon group.

02:54 And carbon groups, as when we talked about aromatics and benzines, they're considered electron pushing, not electron with drying.

03:02 And that's by resonance.

03:04 And because of this, it would be a strong -ish acid, but when we're talking about relativity, this carbon or this carboxylic acid has a fluorine attached to it.

03:17 And that fluorine is very, very electronegative.

03:20 So would it be electron with drying or electron pushing? well, it would be electron with drawing.

03:29 So since it's electron with drawing, because of induction and because of resonance, it will, in fact, just take more of that electron density, making this power stronger acid.

03:46 Let's try another example.

03:51 With these two carboxylic acids, now, both of them have electron withdrawing groups.

03:59 Now, the question is, which one is more electron withdrawing? the chlorine or the fluorine? well, fluorine, if you look on the periodic table, has an electronegativity of fluorine, is about 3 .99 close to 4.

04:20 And chlorine, it has an electronegativity less than that.

04:25 It's more of a 3 .6 or something close...

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