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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Fzang on December 14, 2010, 07:00:04 PM

Title: Quickie: Why is oxazole aromatic? It doesn't fit the reqs?
Post by: Fzang on December 14, 2010, 07:00:04 PM
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Two pairs of pi electrons from the ring itself, a pair from oxygen and a pair from nitrogen. That makes 4 pairs, which shouldn't be aromatic.

But why am I reading "aromatic" wherever I look?
Title: Re: Quickie: Why is oxazole aromatic? It doesn't fit the reqs?
Post by: MissPhosgene on December 14, 2010, 07:18:39 PM
It is aromatic. 3 pi electrons from the carbons in the ring. Two from oxygen, one from nitrogen.
Title: Re: Quickie: Why is oxazole aromatic? It doesn't fit the reqs?
Post by: Hybrid on December 14, 2010, 09:01:34 PM
2 pi electron " c=c" & c=n" lone pair of N in sp2 orbital not p orbital + lone pair of O in p orbital. similar to imidazole see here

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Title: Re: Quickie: Why is oxazole aromatic? It doesn't fit the reqs?
Post by: Fzang on December 15, 2010, 01:27:41 AM
So nitrogen only provides an available lonepair if it has 3 bonds?
Title: Re: Quickie: Why is oxazole aromatic? It doesn't fit the reqs?
Post by: Hybrid on December 15, 2010, 01:57:43 AM
as it "sp2 N" it has 3 sp2 and 1 p so if it make = it will consume the 1 p so every bond after that and its lone pair will be sp2 "not parallel to ring = " so it will be basic.
Title: Re: Quickie: Why is oxazole aromatic? It doesn't fit the reqs?
Post by: cupid.callin on December 15, 2010, 09:10:08 AM
Acc. to Huckel's rules, a molicule should be planar to be aromatic.
As you asked, N should have 3 bonds, it shoud have a pi bons. if the pi bond C=N is made C-N, it wont be aromatic anymore, you can check by making resonating structures.

If bond b/w C and N is single, due to tetrahedral shape, molicule wont be planar anymore.
Title: Re: Quickie: Why is oxazole aromatic? It doesn't fit the reqs?
Post by: Telamond on December 16, 2010, 11:47:21 AM
Just want to mention this (since the op's question is already answered); a molecule doesn't have to be planar to be aromatic.
Barrelene is an example of this.
Title: Re: Quickie: Why is oxazole aromatic? It doesn't fit the reqs?
Post by: jake.n on December 16, 2010, 03:18:49 PM
The hybridization arguments posted above are good.  Typically, if a molecule can be hybridized such that it is aromatic, it will be.  Aromaticity is a strong stabilizing force, and molecules tend to arrange themselves to minimize their energy.