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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: AcceleratorLvL5 on July 01, 2020, 06:44:40 AM

Title: Valid Resonance Structure
Post by: AcceleratorLvL5 on July 01, 2020, 06:44:40 AM

Hello there,

I am doing resonance exercises and wanted to know if the following resonance structure (with a question mark) is valid. (If it isn't could you please elaborate why:)

Thanks!

Title: Re: Valid Resonance Structure
Post by: Babcock_Hall on July 01, 2020, 07:48:46 AM

It is a forum rule that you must give your thoughts before we can help you.  What criteria do you know for judging resonance structures?

Title: Re: Valid Resonance Structure
Post by: AcceleratorLvL5 on July 01, 2020, 09:26:32 AM

Well, in a resonance structure only electrons (and therefore charges) move.
The negative nitrogen has 8 electrons fulfilling the octet rule but only 2 bonds and is therefore negatively charged.
It can then push one free electron pair onto the sp2 hybridized carbon and create a π-bond but due to carbon only being able to have four bonds the π-bond between the two carbons is removed and the electron pair shifts onto the "left" carbon as a free electron pair.

I think the third resonance structure doesn't work since the carbon directly bonded to the nitrogen would exceed the octet rule if it would get another free electron pair from nitrogen, so only the first to should be valid if I'm correct?

Title: Re: Valid Resonance Structure
Post by: Babcock_Hall on July 01, 2020, 10:32:18 AM

I agree.  Sometimes I find it to be helpful to draw out the hydrogens, to make counting the total number of electrons easier.

Title: Re: Valid Resonance Structure
Post by: AcceleratorLvL5 on July 01, 2020, 10:51:59 AM

Thanks for the confirmation :)
I will start drawing them as well (if the structure is more complicated).

Title: Re: Valid Resonance Structure
Post by: rolnor on July 01, 2020, 02:19:17 PM

This can be helpfull:

https://en.wikipedia.org/wiki/Enamine