[DannyBoi]

Hi,

I'm doing problems from Jones Organic Chemistry 4th Ed. Chapter 1, page 45. Problem 1.35 asks:

Use the arrow formalism to write resonance forms contributing to the structures for the following molecules:

For the picture attached, my solutions manual says you'd move the lone pair from the middle N to the double bond on the right to make a triple bond for the first form.

When I did it I just moved the lone pair from the Carbon to the single bond beside it and then just moved on of the double bonds to the rightmost N to make it neutral. Why is my answer incorrect compared to the solutions manual?

Thank you

[Schrödinger]

Hint : Those structures in which an atom has a satisfied octet is more stable than those in which it doesn't.

[DannyBoi]

I see, thank you! I just figured my answer made more sense because it reduced the number of separate charges on the molecule, which apparently is a good thing?

[rabolisk]

You want to form as many octets and have as many elements with a formal charge of 0 as possible. Generally, octets first come. There are cases where you cannot have all elements with a stable octet. For period 1 and 2 elements, though, you should never go above 8 electrons. (just like for H, you would never go over 2 electrons). The solution given will satisfy the octet requirement for all elements, although it will introduce formal charges. The solution you give violates the octet rule in a way that N will have 10 electrons around it, which is not possible.