What is resonance and why is it important in aromatic compounds?

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Hi everybody. Let's take a look at our next question. It says true or false. Resonance is important in aromatic compounds because it depicts sigma bond movement. Well, let's think about what resonance is. And resonance is when we have a model where a single Lewis structure doesn't really present the full picture of how the electrons in a particular molecule are behaving. So an example of a simple case of resonance would be in carboxylate ions. So any R group here and then an O minus, they've got a carbon with a double bond to an oxygen on one side and a single bond to a negatively charged oxygen with three lone pairs on the other. But this molecule doesn't exist just in this form because this isn't how we see its true structure. Instead, the double bond can sort of alternate, you can draw two different Lewis structures where the double bond can alternate between the two oxygens. So we can have another Lewis structure where the negative charges and the single bond is on the other electron on the other oxygen, excuse me. So we have these resonant structures and that expresses the idea that the pi bonds or the pi electrons in that double bond are delocalized. They don't stay just between one carbon and one oxygen. Instead, they sort of, and you can draw with this dotted line showing that they sort of spread around between the two oxygens and the carbon. So they're delocalized over this whole area. So, right, delocalized P electrons. So each of these has sort of a partial negative charge rather than the negative charge residing completely on one oxygen or the other. So we have this resonance that just refers to delocalized pi electrons. And our question specifically asks about aromatic compounds, but we just have a similar phenomenon. So of course, benzene would be perhaps the most famous aromatic compound. And we know it's this ring of six carbons with three double bonds. But again, it exists in this resonance structure or pair of resonance structures where the double bonds can be on the other carbon molecules. So again, rather than just existing as two separate structures or one way of being, these pi electrons are delocalized around the entire ring. And that is key to the properties of aromatic compounds. So when we look at our answer choices, it says true or false or our answers, it says resonance is important in aromatic compounds because it depicts sigma bond movement. But this would be false because resonance depicts pi bond movement. The sigma bonds are unaffected, they remain localized between the two atoms participating in the bond So our answer here is false since it is pi rather than sigma bond movement, that's important. See you in the next video.

What is resonance and why is it important in aromatic compounds?

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Key Concepts

Resonance

Aromatic Compounds

Importance of Resonance in Aromatic Compounds