[ioke09]

How would I draw the best resonance structure that has atoms with formal charges in the question below?

Draw the lowest energy alternative resonance structure for this compound.

In this particular problem, draw the best resonance structure that has atoms with formal charges. Please see image of compound below.



Here's my first attempt at this question:



Can anyone demonstrate how to start this problem?

Thanks for any help.

[james_a]

OK, so what's the biggest rule for drawing resonance structures? We can't break *single bonds*. And we certainly can't remove atoms.
You're only allowed to move electrons around.

You might find this series of videos helpful (1-4). http://bit.ly/oM1rHV

[ioke09]

Here's my second attempt, but I'm not sure how to get charges on atoms.

[Honclbrif]

Draw some lone pairs on the oxygen. Use a curved arrow to push them around. If they go to where you've pushed them, where do other electrons have to go?

For a quick starter practice, try drawing the resonance forms of hydroxy ethylene.

[ioke09]

There are two lone pairs on the oxygen, but wouldn't moving those change the overall charge of the resonance structure? Using curved arrows gives me the same message that the atoms are not charged.

[discodermolide]

There are two lone pairs on the oxygen, but wouldn't moving those change the overall charge of the resonance structure? Using curved arrows gives me the same message that the atoms are not charged.

Try moving one of the lone pairs into the C-O bond and see what you must do to the pi electrons in the aromatic ring, then place the appropriate charges on the atoms involved.

[Honclbrif]

"There are two lone pairs on the oxygen, but wouldn't moving those change the overall charge of the resonance structure?"

If you create a - charge on one atom, you MUST have a + charge on another. If you ever find yourself creating a charge without an opposite one to balance it, go back and work out the formal charges on everything you pushed an atom too or from.

[bigmo89]

I know this isn't my question, but we recently went over resonance structures in my class and to me it looks like the first attempt is right. Being able to draw resonance structures is supposed to be review, but it was never covered in any of my general chemistry classes.

It looks like he just moved the double bond twice, to the oxygen making it negative. The carbon lost a bond so it would become positive. So there is a conservation of charge because the molecule is neutral as it began.

[Honclbrif]

Atoms never move in resonance structures. If you superimposed all of the resonance structures of a molecule, the only thing that would be different is the locations of some bonds. In the first post a hydrogen has migrated from O to C, making this an invalid resonance structure.