Radical Resonance Help

[stitchattack]

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Can someone explain the process of resonance that I seem to be missing? In the solution I get the first two resonance on top but the one they drew on the bottom confused me.

Basically, my understanding of resonance is that it can go bond to lone pair, lone pair to bond, and bond to bond.

Also, is there an easy way to remember how to draw resonance structures? I can somewhat do the easy ones but with complicated structures, I get lost.

 

[JMMTB]

With resonance structures we are looking for what atoms in the molecule have a p orbital to conjugate into. Like you said you can go from lone pair to bond and bond to bond, with the example of the radical, the bottom resonance structure is the result of the middle structure's bond splitting.

In radicals electron pushing arrows are half barbed (one sided) to represent one electron moving. The answer key doesn't show one more resonance structure as well as the electron pushing arrows.

As far as the other answer choices, it is really bad to have a radical or charge on a double bond. Adjacent is better because of the resonance. And if the radical is separated by an sp3 carbon, then it can't resonate in.

 

[stitchattack]

Thanks JMMTB. Correct me if I'm wrong, for resonance structures for radical pushing when double bond(s) exist in the structure, you move the radical 2 C's down so the double bond can move to an adjacent C away from the radical?

 

[JMMTB]

Yes, exactly!

 

[stitchattack]

Thanks so much!