That would give nitrogen 4 bonds and no formal charge, which violates the octet rule and formal charge rules. If nitrogen is making 4 bonds (2 double bonds), it’s sharing 8 electrons, but nitrogen only has 5 valence electrons. Valid resonance structures share the same total number of electrons, same atom connectivity, and obey the octet rule.

The two resonance forms shown, where the double bond switches between oxygens are the only valid ones.

After you watch this I highly recommend the next two videos they will help you practice these concepts even more:

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Practice Problem: Drawing All Resonance Forms That Stabilize a Carbocation

Hey Daniella, The electrons are still there, what you'll notice as we move through Organic Chemistry is that the lone pairs won't always be shown but you will still be expected to know that they are there. It's like the hydrogens on Carbons that we saw aren't shown (this will be explained later on if you have gotten there yet) and it's a quicker way to draw structures. 

We don’t currently have a video on that topic, I’m so sorry about that. But you can get an instant explanation from our AI Tutor at any time. It’s designed to walk you through concepts step-by-step and is available 24/7.

We are so glad these videos have been helpful! Oh wow taking both Ochem 1 and 2 at the same time is intense!

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Hey Paola,

The electrons are still there, what you'll notice as we move through Organic Chemistry is that the lone pairs won't always be shown but you will still be expected to know that they are there. It's like the hydrogens on Carbons that we saw aren't shown (this will be explained later on if you have gotten there yet) and it's a quicker way to draw structures. 

Joelle question 9 at 44:13 of the below video is another example of reactions of dienes.

Stephanie Cervino When the entire molecule's overall net charge is 0, which it is in this case, then it is preferred to have formal charges of 0 for each atom. Does that make sense? 

Yes that is correct, Cl is a good leaving group this is why it leaves to make room for the reformation of the S=O bond. 

Yes, since the Williamson Ether Synthesis proceeds via an SN2 mechanism, the nucleophile will indeed perform a backside attack on the electrophile (typically a primary alkyl halide or tosylate).