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Topic: Is this structure possible?  (Read 3744 times)

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Offline blueblueblue

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Is this structure possible?
« on: January 16, 2011, 12:29:10 AM »
For my class I need to come up with a challenging question and for this assignment my professor prefers questions with no definite answer.  The whole point is to come up with subjective answers which are not yes/no.  I am just in the 2nd term of Ochem and am still a beginner.
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My question is:

You were given this structure and asked to draw a resonance structure with an octet on every atom and no formal charges.

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BUT my real problem is that in the picture nitrogen does not satisfy the octet rule.  It only has 6 electrons instead of 8.  Nitrogen is supposed to have 8 electrons, so it is missing a lone pair or a hydrogen.  Is this structure even possible?  Or, for the sake of the question...does it not matter?  Is it okay if it doesn't satisfy the octet rule?  Or even, is there anything that I am missing here about nitrogen?

I really appreciate if you can give me any tips on this.

Thanks in advance!

Offline jelee

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Re: Is this structure possible?
« Reply #1 on: January 16, 2011, 12:50:29 AM »
Yes, this structure is possible.

The main reason this is possible is because of resonance. If you look at the alternative resonance structure, there would be a double bond connected to the oxygen and a single bond connected to the nitrogen. The problem with this structure however is that there would be a positive charge on oxygen and a negative charge on oxygen. This wouldn't be the best structure to draw because oxygen is more electronegative than oxygen, and therefore should have the negative charge.

It's best to think of the octet rule as a guideline rather than a law. While yes, it is best to give atoms a full octet and to reduce formal charges, there are still exceptions, such as this structure.

Offline nox

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Re: Is this structure possible?
« Reply #2 on: January 16, 2011, 02:38:40 AM »
Actually if you draw the other resonance structure with a double bond to O, the molecule will be charge neutral. Nitrogen will have 2 lone pairs and a single bond, so the formal charge is 0. BUT nitrogen will still only have 6 electrons.

In fact I don't think it's possible to draw a resonance structure with a full octet on every atom for this molecule, let alone having no formal charges.

Offline blueblueblue

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Re: Is this structure possible?
« Reply #3 on: January 16, 2011, 05:20:36 PM »
Thank you very much for going over my question.

I know Nitrogen does not satisfy the octet rule in the picture, but if this were possible, what about a three cyclic ring between nitrogen and oxygen and a carbon.  I don't if it it would form a three cyclic ring, but if I draw a single bond from nitrogen to oxygen, then it satisfies the octet rule.

Offline Jorriss

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Re: Is this structure possible?
« Reply #4 on: January 16, 2011, 11:03:50 PM »
That's not a resonance structure. Resonance structures include the movement of pi bonds and lone pairs, not the formation of sigma bonds. It's a good observation, just not a resonance structure by definition.

Offline blueblueblue

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Re: Is this structure possible?
« Reply #5 on: January 17, 2011, 03:14:29 AM »
Thank you very much for your post.  I understand that the cyclic formation between the three atoms are not resonance since it will not have a sigma bond...  But then what could you call the formation?  Are there any reactions like this?   

Offline ooosh

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Re: Is this structure possible?
« Reply #6 on: January 17, 2011, 07:44:02 AM »
No one  above hits the point. It's actually Nitrene(6 electrons) ,which is very unstable and converts to isocyanate immediately.If you have a name reaction book,you can find it in the Curtius ,Hofmann,Schmidt and Lossen reaction.

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