List the following in order of decreasing delocalization...

Key Concepts

Electron Delocalization

Electron delocalization refers to the distribution of electrons across several atoms rather than being localized between a single pair of atoms. This phenomenon allows molecules to stabilize by spreading out electron density, reducing electron–electron repulsions, and enhancing overall molecular stability.

Resonance Stabilization

Resonance stabilization describes the increased stability of a molecule due to the representation of its electron distribution by multiple valid Lewis structures. These resonance forms contribute to a resonance hybrid that reflects a delocalized distribution of electrons, providing extra stabilization compared to any single contributing structure.

Conjugation

Conjugation is the overlap of adjacent p orbitals in molecules, typically seen in alternating single and multiple bonds. This overlap enables the electrons to be shared or delocalized over multiple atoms, thereby lowering the energy of the system and contributing to its stability.

Aromaticity

Aromaticity is a special type of conjugation found in cyclic molecules that meet specific criteria (such as Hückel's rule). Aromatic compounds exhibit significant delocalization of electrons, resulting in remarkable stability and unique chemical properties compared to non-aromatic analogues.

Transcript

00:01 Let's start by drawing the resonant structures for each one.

00:03 So right off the bat, we have a hydrogen bonded to a carbon, bonded to an oxygen, which we know has a negative charge on it, and we have a double bond off to an oxygen, which is going to have two lone pairs on it.

00:21 If we think of a resonant structure for this, we can pull a set of electrons down from here and bump these electrons up here, which is going to give us a structure that looks like this, where we've just moved the location of that double bond.

00:39 So these resonant structures are going to contribute equally due to the fact that they are effectively the same molecule that we've just gone ahead and rotated.

00:51 But don't think they're actually the same structure, because that charge is going to be split equally between these two oxygens.

01:04 Okay, let's go on and draw the next one, which is that of a carbonate ion, it looks like.

01:11 We have an oxygen with a negative charge on it.

01:16 So that will look like so.

01:18 And that's bonded off to a carbon with a double bond to an oxygen, which has two lone pairs on it.

01:26 Try not to invade the space of this molecule up here.

01:29 And then we have a bond down to another oxygen here.

01:33 And that one also has a negative charge.

01:36 So the carbonate ion, we do already know, has three different resonant structures, as gone over in problem 7 from this textbook.

01:47 But i'll go through it again briefly here.

01:50 If we pull a set of electrons up from here, we can pull a set down from here.

01:54 And that'll give us a single bond up to this oxygen in a structure that's going to look like this, where we have the negative charges on these two oxygens instead, and a double bond sitting right over here with two lone pairs.

02:14 Then if we bump this pair of electrons back up, we can pull down some electrons from this oxygen, and that's going to move the negative charge from the right.

02:25 Right hand side over to the left, and that's going to look like this.

02:31 We have negative charge up on top, carbon in the middle, single bond to an oxygen down here, that's going to hold the other negative charge, and a double bond off to this oxygen here.

02:44 And as we've already seen in the carbonate ion, the carbonate ion is going to have an equal amount of contribution from each three of these resonant structures, giving us a total charge of negative two -thirds on each of these oxygens in the total contribution.

03:03 So that's something to keep in mind is that these are all equally valid resonant structures.

03:09 And let's move on now to our last molecule, which it looks like is hydrogen bonded to a carbon, bonded to an oh group, bonded to an oxygen.

03:26 So if we go ahead and pull up this bond here, we can move some electrons up onto this oxygen...

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