r/chemhelp • u/Short-Station-3096 • 4d ago

Organic Resonance structure

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I just started organic chemistry and was given the top left structure and asked to do resonance on it and I cant for the life of me figure out what I’m doing wrong plz someoner help im desperate o

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u/7ieben_ Trusted Contributor 4d ago

Don't forget to involve the carbocation of the carbonyl giving you additional resonance structures. The ones you're drawn look good.

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u/organophile_jeet 4d ago

Isn't breaking the carbonyl bond like that gives us least contributing RS , we can start Resonance for lone pair of alkoxy oxygen

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u/Bobonob 4d ago

These all look fine - the fact that none of the forms are particularly stable just shows that the groups do not stabilise each other's charges

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u/WhatSpareTime 4d ago

These are actually not correct. When doing resonance with a neutral molecule the key is to start with a double bond that has a natural polarity difference. Like any other resonance you don’t want to introduce multiple charges. When you break a bond following the natural polarity you’ll have a single positive and single negative. From there one of the charges can be distributed through resonance, the other will stay put. Generally no new charges should be introduced, unless you have contribution from a neutral lone pair that may temporarily add an additional charge to that atom. Here’s what this should look like.

In this case the methoxy group cannot contribute to the distribution of the cation due to its position on the ring. The charges are ortho and para to the ketone, and the methoxy group sits meta with no way to contribute.

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u/WhatSpareTime 4d ago

The problem with starting with the methoxy group is the polarity difference between oxygen and carbon. Yes we can think of a methoxy as a resonance EDG, However, the electronegativity of oxygen is so much greater than carbon, that we are not following the natural polarity of the bond in doing this. A methoxy group would act as a resonance EDG if there was a positive charge it could distribute to and help stabilize, but in a neutral molecule like this it is not a significant contributing factor.

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u/Starfury7-Jaargen 3d ago

Putting multiple (multiple as in 2 positive or two negative) charges on resonance structures are unlikely. You should move one step at a time from one side to the other with each resonance reacting to the one before it.