Energy of Resonance Structures

[geeyouknit]

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So, I think I know the answer to this question,
but do individual resonance structures have a energy assigned to it, like a quantifiable number?

I always thought that you could talk about structures that are more stable have less energy, but you couldn't really assign a specific number because discrete structures don't exist.

Thanks

 

[BerkReviewTeach]

So, I think I know the answer to this question,
but do individual resonance structures have a energy assigned to it, like a quantifiable number?

I always thought that you could talk about structures that are more stable have less energy, but you couldn't really assign a specific number because discrete structures don't exist.

Thanks

For a compound, you can measure its deltaG of formation and assign it an energy number accordingly. By comparing the deltaG of formation for two isomers (one with conjugation and one without it), you can make a conclusion about the impact of such things as resonance (conjugation).

But resonance is a theoretical perspective and you cannot actually isolate one resonance structure from another one to study it, so there is no way to measure their energy empirically. There are computer programs that can assign energy values to structures, so I guess in theory one could assign a numerical value to each resonance structure. I'm not sure I've seen that done, but it's an interesting thought.