Resonance Stabilization

Once again, it's been a while. I had so much fun with the Lewis structures post that I wanted to make a new post the very next day, but other things kept getting in the way. Well, I'm not putting it off anymore. My introduces resonance after introducing Lewis structures, so I suppose I'll follow its lead...

Many molecules, both organic and inorganic, are resonance stabilized. Such molecules cannot be represented by a single Lewis structure. For that, we can use resonance structures—if we want to. I don't really like resonance structures myself. But you know, whatever works. Before I go any further with resonance structures, I must explain why they're used at all. They exist because of the delocalization of electrons. Delocalized electrons aren't sitting on any one atom and they're not locked into any one bond. That's why we use the word "delocalized." It's like they're spread out over multiple atoms as one big forcefield of negative awesomeness. I don't know. Let's just move on to the example.

The example my book uses is this anion. Don't worry about its name because I don't know its name either. It's the conjugate base of formamide and it's an anion, but beyond that, I have no idea. Here's are the resonance structures...
Yes, the circled "-" sign is a negative charge. That was obvious, right? That double-headed arrow indicates that these are resonance structures. The important thing to realize is that these structures aren't two molecules. They're representing the same molecule in two different ways. The electrical charge is in two different places, but all of the atoms are in the same places. The first structure makes the oxygen the center of negative charge. The second structure makes the nitrogen the center of negative charge. In actuality, the negative charge is distributed between those two (and in this case, it will be slightly more centered on the oxygen because oxygen is more electronegative than nitrogen).

Resonance structures are not real. My professor compared it to describing a rhinoceros, to someone who had never seen one, as a cross between a unicorn and a dragon. Yeah, that doesn't make any sense. He realized that after he said it. But he was trying to think of a more everyday example of using two fictitious things to describe one real thing. Resonance structures aren't always in pairs, though. Many molecules have three resonance structures.

So yeah, not real. Resonance structures. The bond between the carbon and the oxygen isn't actually a double bond. And the bond between the carbon and the nitrogen isn't a double bond either. It's more like the bond between carbon and oxygen is a little bit more than a 1.5 bond and the bond between the carbon and the nitrogen is a little bit less than a 1.5 bond. I don't know the actual numbers. It's possible to take a measurement, but I don't have the equipment or the expertise, so shut up. We'll just pretend that it's exactly 1.5 on both, even though I know that it isn't. Actually, why didn't this stupid book just use an example where that was the case? I mean, there are cases like that. This molecule isn't one of them. Anyway, it's more like those bonds are each 1.5 bonds. But Lewis structures don't have a way of representing fractional bonds, so we need a way to represent what's going on here. Some day, I'll fix the notation in chemistry. Until then, we're stuck with resonance structures.

This post was probably kind of confusing. I know I get resonance structures. But maybe you don't. Remind me to help make this post more clear. Right now I need sleep. I'm totally going to write about isomers tomorrow.