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Topic: Why is imidazole aromatic?  (Read 12677 times)

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Offline CrimpJiggler

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Why is imidazole aromatic?
« on: October 14, 2011, 08:40:16 PM »

I can see there are 4 pi electrons from the 2 double bonds. The nitrogen with the hydrogen attached has a lone pair of electrons to contribute bringing to total of pi electrons up to 6 but what about the lone pair on the nitrogen at position 3? Doesn't that bring the total of pi electrons up to 8?
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Offline Fluorine

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Re: Why is imidazole aromatic?
« Reply #1 on: October 14, 2011, 09:07:18 PM »
The total, yes it would be 8 but how many are actually contributing? Think about the differences of the two nitrogens' geometries; one is sp3 and the other is sp2. How would their lone pairs be aligned? Try to draw it out if it helps.

You can compare your sketch to this: imidazole (3D)
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Offline fledarmus

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Re: Why is imidazole aromatic?
« Reply #2 on: October 15, 2011, 09:29:00 AM »
Just a little quibble Fluorine - to be aromatic, both nitrogens appear to be sp2 hybridized. The difference lies in which orbitals the lone pair of electrons occupies and where those orbitals are oriented in space.
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