sdnstud

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quick question. a nitrogen (N) attached to 2 carbons and have 2 lone pairs is sp3. But my instructor says if the same nitrogen is part of an aromatic ring, it is sp2. is this true?
 

TripleDegree

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Unless perhaps there was a double bond involved somewhere?

What form would N appear on an aromatic ring? As an NH2 group?
 
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CanIMakeIt

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Originally posted by sdnstud
quick question. a nitrogen (N) attached to 2 carbons and have 2 lone pairs is sp3. But my instructor says if the same nitrogen is part of an aromatic ring, it is sp2. is this true?
only if there is a possibility of donating the lone pair for the stability of aromatic ring then those electrons become delocalized and N is considered sp2 otherwise it will still be sp3

good example is coffee structure:

http://www.brynmawr.edu/news/ask/index.shtml

In the ring on the left.....at first glance you will think that N is sp3 hybrid but N gives its electrons to the ring and O becomes negative charge..... when both N do that, the ring is stabilized and electrons fron N lone pairs are delocalized making it sp2

I hope it was helpful
 

krull

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If the resonance structure of the the molecule is more stable when Nitrogen has a double bond such as R2N=R then nitrogen is Sp2 hybridized. If the resonance structure of the double bonded Nitrogen atom is a less stable product than its single bonded resonance form, then the molecule is Sp3 (R-N-R)
 

jhk43

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Originally posted by CanIMakeIt
only if there is a possibility of donating the lone pair for the stability of aromatic ring then those electrons become delocalized and N is considered sp2 otherwise it will still be sp3

good example is coffee structure:

http://www.brynmawr.edu/news/ask/index.shtml

In the ring on the left.....at first glance you will think that N is sp3 hybrid but N gives its electrons to the ring and O becomes negative charge..... when both N do that, the ring is stabilized and electrons fron N lone pairs are delocslized msking n sp2

I hope it was helpful
coffee is aromatic rite?

4(1) + 2 = 6?
 

Nuel

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Originally posted by jhk43
coffee is aromatic rite?

4(1) + 2 = 6?
Actually on the picture there are 10 aromatic pi electrons. I don't think aromaticity is tested this MCAT season.
 

liverotcod

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In pyridine, for example, the Kekule structure is drawn with one single bond and one double bond--a fiction, obviously, but it does suggest the correct answer of sp2. In pyrrole, which is a little weird, you get (technically) sp3 hybridization but the extra stability of the aromaticity forces the non-bonded pi electrons to delocalize and take on sp2 character.

See this word doc about aromatics (page 20)
 

babinski bob

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By definition, one of the criteria of aromaticity is planarity. Therefore all atoms part of an aromatic system are sp2 hybridized.
 
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