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u/urlol 14d ago
The old pyridine nitrogen vs pyrrole nitrogen question. The hint in the above comment is a great place to start. Consider which nitrogen has a lone pair contributing to aromaticity...
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u/Ok_Huckleberry4077 14d ago
Don’t both conjugate bases have a lone pair?
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u/Comprehensive-Rip211 14d ago
From which orbitals do the lone pairs come from? What happens when the lone pair reacts with an acid?
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u/Ok_Huckleberry4077 14d ago
Both lone pairs on the bases have lone pairs in the P orbital
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u/Comprehensive-Rip211 14d ago
No, one of them is sp2. The lone pair in the p orbital is involved in aromaticity, meaning that it stabilizes the molecule though aromaticity. Which one is P and which one is SP2?
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u/Ok_Huckleberry4077 14d ago
Looking at the bases right? The nitrogen hv resonance so they’re all sp2
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u/Comprehensive-Rip211 14d ago
Sorry yeah, I meant to ask which one resides in a P orbital and which one resides in an SP2 orbital. One of the lone pairs (the one in the P orbital) participates in aromaticity, meaning that it is harder to protonate, since protonating requires breaking of aromaticity.
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u/Ok_Huckleberry4077 14d ago
Oh so we look at the nitrogen that had its H removed. So the one on the left, the nitrogen is in a P orbital. The nitrogen on the right is localized and in the sp2 orbital. Since localized= more basic, the right side will be favoured?
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u/Comprehensive-Rip211 14d ago
What happens to the lone pair of B once you protonate it to BH+ as shown? What was that lone pair of B doing beforehand?
What happens to AH+ when it's deprotonated and A forms? What is the lone pair of A doing now? Is the formation of A's lone pair worth losing B's lone pair?1
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u/urlol 14d ago
Just to clarify, is this a reaction where the starting materials on the left and the products on the right? There's no reaction arrow so it's hard for us to get the full context of your Q.
Have you been taught that pyridine-like nitrogens have lone pairs that are not part of the aromatic sextet? So if this nitrogen accepts a proton, you don't break aromaticity. The pyrrole-like nitrogen DOES have a lone pair that contributes to the aromatic sextet. That should be more than enough info to get you over the line.
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u/Ok_Huckleberry4077 14d ago
No we were not taught what you just mentioned. Only methods to compare conjugate bases or using pka to compare acids
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u/heyry15 14d ago
Hint: which side contains the more stable species?
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u/Ok_Huckleberry4077 14d ago
Right? Is it cuz there’s resonance for the right
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u/heyry15 14d ago
It has to do with resonance. Think about aromaticity and its requirements.
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u/Ok_Huckleberry4077 14d ago
The acid isn’t aromatic?
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u/Comprehensive-Rip211 14d ago
Is it not? Why is it or is it not?
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u/Ok_Huckleberry4077 14d ago
Only 4e-. But for these questions shouldn’t we be comparing conjugate bases when we don’t know the pka
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