DAT O.Chem 2016 Question #71

[tony729]

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I am a bit confused on the hybridization of the nitrogen, to me it looks like it would be sp3 since there are 3 bonds and a lone pair.

 

[Ashish]

Due to Resonance, there is electrons delocalization in the 5 membered ring, and that is why it its not sp3 hybridized (the one pair does not just stay with Nitrogen). Another way to look at this is Aromaticity. The 5 membered ring is Aromatic with conjugated double bond system, less than 7 members in the ring and odd number of electrons pair ( only 1 pair is counted to determine Aromaticity) and hence, the member in the cyclic ring cannot be sp3 hybridized.

 

[tony729]

Thank you! Also, i would like to is a lone pair always in the p orbital?

 

[tony729]

Thank you! Also, i would like to is a lone pair always in the p orbital?

 

[Ashish]

Yes, remember that electrons in s-orbital (smaller orbital that is closer to nucleus) experience greater nuclear charge and hence cannot "per say" delocalize!

 

[tony729]

Great thanks buddy

 

[gangazi]

lone pair is not always in p orbital...

 

[gangazi]

dont listen to the devil

 

[DAT Destroyer]

I am a bit confused on the hybridization of the nitrogen, to me it looks like it would be sp3 since there are 3 bonds and a lone pair.

Not a chance. This N is sp2 because if you consider the RESONANCE structure, it will reveal a molecule that has a N with significant double bond character. For practice, I want you to look up the structure of an AMIDE. You will see a N with 3 bonds and a lone pair. This N is also sp2 since the amide has significant structural contribution possessing double bond character.

Hope this helps.

Dr. Romano