quick organic question

[russellfx]

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me and my friends have been trying to figure out why this is what it is:

The nitrogen atom in aniline (nitrobenzene) is :

sp2 hybridized

Why is it not sp3?

 

[QBWR12]

Yo,

The reason I think you're having some confusion is because aniline and nitrobenzene are actually two completely separate compounds. You're right that the aniline nitrogen IS sp3 because it's an amino group attached to a benzene ring (aminobenzene), but the nitrogen in nitrobenzene is sp2 because it's a nitro (NO2) group attached to a benzene ring.

Take a look at these sites (I know it's wikipedia but in this case it's credible):
http://en.wikipedia.org/wiki/Nitrobenzene
http://en.wikipedia.org/wiki/Aniline

Hope this helps!

 

[russellfx]

Yo,

The reason I think you're having some confusion is because aniline and nitrobenzene are actually two completely separate compounds. You're right that the aniline nitrogen IS sp3 because it's an amino group attached to a benzene ring (aminobenzene), but the nitrogen in nitrobenzene is sp2 because it's a nitro (NO2) group attached to a benzene ring.

Take a look at these sites (I know it's wikipedia but in this case it's credible):
http://en.wikipedia.org/wiki/Nitrobenzene
http://en.wikipedia.org/wiki/Aniline

Hope this helps!

lol oops i wrote that wrong. i meant to say aminobenzene... which btw according to my book and answer key is sp2?

 

[QBWR12]

Answer key is definitely wrong, you're definitely right. No question.

 

[1956Goldtop]

Its possible that the lone pair remains unhybridized so you have the 3 bonded electrons as sp2 hybrids and the the pure 2p electron pair... but maybe not I don't know.

 

[tiedyeddog]

Its possible that the lone pair remains unhybridized so you have the 3 bonded electrons as sp2 hybrids and the the pure 2p electron pair... but maybe not I don't know.

I was thinking the same thing, but I believe it doesn't occur because then it wouldn't be aromatic? I don't know if having the NH2 already makes it nonaromatic due to being non-cyclic., eh. I just took a test on this stuff and I'm trying to forget it...

 

[JA Prufrock]

Its possible that the lone pair remains unhybridized so you have the 3 bonded electrons as sp2 hybrids and the the pure 2p electron pair... but maybe not I don't know.

why does that happen though? Does the -NH2 stay in the sp2 so that it can get involved in the conjugated pi system? That wouldn't make sense since it's not going to fit the 4n+2 rule for aromaticity with 8 pi electrons.

Beats me, OP. I'm curious to hear the answer though.

 

[seebelcherrun]

A resonance form could be made that has an sp2 Nitrogen, although I think aromaticity may be lost, and you'd also be placing a pair of electrons on one on the carbons and a positive charge on the nitrogen. So that may be a possibility, or it could just be a typo.

 

[1956Goldtop]

Having a pure P orbital with lone pair electrons won't affect the aromaticity of the ring because the nitrogen isn't part of the ring system. If we were talking about something such as imidizole, then yes, the hybridization of the orbitals affects the aromaticity of the molecule.

As for a possible reason why the nitrogen atom would go with sp2 hybridization rather than sp3, I have no idea. It is hard to predict these things. One possible reason is that keeping the one pure p orbital keeps the entire molecule planar (which now that I think about it, probably doesn't matter). It might also be a steric issue, because keeping the N atom sp2 hybridized will keep all the substitutents 120 degrees from eachother. ::

 

[surfstarj]

whoever said overlap got it.

hope this works. never too old for a friendly session with the molecular model kit.

 

[1956Goldtop]

makes sense, it provides an extra unit of conjugation.

 

[QBWR12]

Ah! Now i feel like an idiot after seeing that textbook link. I taught this earlier in the semester! That explanation makes total sense. Whoops! lol