Conjugated vs aromatic?

[TheRelevant]

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In ch 1 of TBR, they present conjugation and aromaticity is as if they're mutually exclusive processes. I understand what aromaticity is, but would anyone be kind enough to shed some light as to what conjugation is? It sounds super familiar from intro O-chem, but it's been so long and I can't seem to find anything regarding conjugation on the internet.

 

[Alucard6]

So aromaticity is essentially a subset of conjugation, probably the most stable type of conjugation you will see. So it makes sense to talk about conjugation first then say how aromatic compounds fit into the mix.

So conjugation is repeating units of p-orbital overlap. In other words, it is the double bonds throughout all the compounds. For conjugation to occur, you have a single bond followed by a double bond then back to a single bond and the pattern repeats. So it is a repeating pattern.

Aromatic compounds are compounds that follow Huckel's rule (4n + 2) and just so happen to alternate completely with conjugation patterns. As a result, these compounds are super stable.

Man, I feel like it is so much better to draw it out and explain, but I hope that helps!

 

[TheRelevant]

Hey Alucard! That definitely helped a TON. Just to confirm: conjugation is simply electron delocalization due to p-orbital overlap of double bonds alternating with single bonds? If that's the case, I am guessing lone pairs in p-orbitals would also be able to conjugate, right?

I was almost going to ask you why p-overlap of adjacent atoms wouldn't be conjugative. ALMOST. Hahaha 😛 (if anyone is as sleep deprived as me and doesn't get it, its because that setup would create pi bonds).

 

[Alucard6]

Hey Alucard! That definitely helped a TON. Just to confirm: conjugation is simply electron delocalization due to p-orbital overlap of double bonds alternating with single bonds? If that's the case, I am guessing lone pairs in p-orbitals would also be able to conjugate, right?

I was almost going to ask you why p-overlap of adjacent atoms wouldn't be conjugative. ALMOST. Hahaha 😛 (if anyone is as sleep deprived as me and doesn't get it, its because that setup would create pi bonds).

Yes to the part you are confirming. Just like aromatic compounds, the double bonds are really helpful for the electron delocalization.

So yep! The lone pairs are what allow the molecule to conjugate. These lone pairs essentially spread throughout the molecule.

 

[TheRelevant]

Thanks a bunch! 🙂

Orgo is really starting to grow on me.

 

[Alucard6]

Thanks a bunch! 🙂

Orgo is really starting to grow on me.

Yeah I love the subject matter. You can memorize it, sure, but really sitting down and understanding mechanistically what is happening really shows the beauty in how we can understand things on a microscopic level.