Draw as many resonance structures as you can for the following species:

Name: Problem 34, Chapter 2: Organic Chemistry
Uploaded: 2020-05-08T02:02:25-08:00
Duration: 8 min
Channel: Bobby Barnes
Description: Draw as many resonance structures as you can for the following species:

Draw as many resonance structures as you can for the...

Key Concepts

Resonance Structures

Resonance structures are different Lewis structures for a molecule that cannot be accurately depicted by a single structure. They represent the delocalization of electrons within molecules and help illustrate how electrons can be spread over two or more atoms, resulting in a more stable electronic configuration than any single contributing structure would suggest.

Electron Delocalization

Electron delocalization refers to the spreading of electron density over two or more atoms, which can occur in systems with conjugated pi bonds or lone pairs adjacent to multiple bonds. This phenomenon stabilizes the molecule by lowering its overall energy and is a fundamental aspect in understanding resonance.

Formal Charge Distribution

Formal charge distribution involves calculating and assigning the formal charges to atoms within a resonance structure. These charges help in evaluating the stability of each structure, as the most stable resonance forms are usually those that minimize formal charges and place any negative charges on more electronegative atoms.

Octet Rule

The octet rule is a guideline that atoms tend to form structures that give them eight electrons in their valence shell, similar to the electron configuration of noble gases. When drawing resonance structures, it is important to ensure that, whenever possible, atoms fulfill this rule, as adherence generally contributes to the overall stability of the molecular structure.

Major and Minor Contributors

In resonance theory, different resonance structures contribute unequally to the overall hybrid. Major contributors are those structures that are lower in energy, have minimal formal charges, and obey the octet rule, while minor contributors are less stable and have greater charge separation. Understanding the difference between these contributors is key to predicting the true electron distribution in a molecule.

Transcript

00:01 They want us to draw as many resident structures as we can for each of the following species.

00:05 So let's go ahead and start with a.

00:07 So now remember for resident structures, we can only move electrons, and we can't create new bonds.

00:15 So let's see what we can kind of do.

00:17 Well, the only carbons that are really, or atoms that are sp2 in this, are going to be along this area right here.

00:27 So this is the only place we could really do resonance since that other carbon is sp3.

00:32 So what we can do is move this to there.

00:39 And in doing that, though, this carbon is going to have five bonds to it, which it won't like.

00:44 So then we would want to pop that up like that, and that oxygen would gain an extra loan pair.

00:52 So let's go ahead and draw that out.

00:53 And i'm just going to draw the bond line for this.

00:55 So you have our carbon.

00:58 We don't need that.

00:59 So it would look like this.

01:01 But now there's a double bond going from the carbon.

01:04 To that carbon and then a single bond to the oxygen but now it's going to have three loan pairs and a negative charge so this is going to be the resident structure and it doesn't look like we have any other resident structures we can form for a so let's go ahead and move on to b so let's first go ahead and identify well where can we do residence for this kind of like what we did over there well anywhere we have like a double bond positive charge or negative charge or loan pairs i should say we'll be able to so it's just those carbons right there so let's go ahead and first move this lone pair to here but in doing that now i'm sorry not to there to this bond right here but in doing that this carbon now is going to have five bonds because even though we didn't draw it that carbon so has hydrogen on it and i don't know why in the structure they give, they have those hydrogens over there.

02:06 So i'm just going to go ahead and erase these because no reason to draw those out, really.

02:16 But so we go ahead and do that.

02:20 And so we get our first resident structure, which is going to be.

02:28 So we have the double bond there.

02:30 Oh, actually i forgot to pop this up to there.

02:35 So we would have the lone pair here now and we still have our double bond on the bottom there and well we could move this lone pair here to form the double bond but then that carbon has too many bonds so we can pop that double bond up to right there and doing that is going to give us so the top double bond hasn't changed now we have a double bond on the side there and then we have our loan pair on the very bottom and that looks to be all of the different resident structures that we could form for this one.

03:13 Now let's go ahead and go to the next set.

03:20 So in this case, notice that this looks pretty symmetric in the sense of, well, it's just nitrogen's attached with two hydrogens.

03:35 So it would make sense maybe for our first resin structure to move the double bond to the nitrogen.

03:43 And then we would move one of the lone pairs from the nitrogen's down like this here and then form a double bond.

03:53 So we'd have nitrogen, nitrogen, nitrogen.

03:59 All of them have two hydrogens on them...

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