Confused about resonance structures

[hannoe]

Have I understood correctly that the resonance hybrid orbital does not represent any actual orbital (with new shape) in the molecule? If a new orbital would form then only two electrons could be there but there are many examples where different pair of electrons can go an occupy the same orbital in different resonance structures (e.g. conductive polymers could not function otherwise). Moreover if one huge hybrid orbital would form then it could be very big which leads to larger energy level for electrons as more nodes must form, which means higher frequency which mean higher energy...

Meaning, the electron pairs that can move around can be only in pi-bonds and AO-s just like in resonance structures. But the energy difference between these orbitals is very small so the electrons can move very fast between them. As a result the molecule cannot be though of as one resonance structure but the combination of many. Is this correct?

[studiot]

1 hour ago, hannoe said:

Is this correct?

No.

You have mixed up and confused several different concepts or models.

We have several because no model is perfect so we select the one that most suits our current needs.

[studiot]

2 hours ago, studiot said:

No.

You have mixed up and confused several different concepts or models.

We have several because no model is perfect so we select the one that most suits our current needs.

As in Hybridisation, Delocalisation per Pi bonding and Resonance.

[hypervalent_iodine]

16 hours ago, studiot said:

No.

You have mixed up and confused several different concepts or models.

We have several because no model is perfect so we select the one that most suits our current needs.

Why do you think this is not correct? It reads mostly fine to me. 

[studiot]

9 hours ago, hypervalent_iodine said:

Why do you think this is not correct? It reads mostly fine to me. 

 

Would you agree with the first line then?

 

On 24/06/2018 at 8:12 AM, hannoe said:

Have I understood correctly that the resonance hybrid orbital does not represent any actual orbital (with new shape) in the molecule?

 

One of the characteristics of resonance structures is the change in bond length from the formative resonance structures.

But it does IMHO show Hannoe has not properly distinguished between atomic orbitals, hybrids orbital, molecular orbitals (and says so her/his self).

 

I was just waiting for more questions from the OP about what I said.

 

There have been too many instances just lately where a question was asked and I or others put significant effort into an answer for an OP who never came back.

 

It is, however, a good subject for discussion that may also benefit others.

Edited June 25, 2018 by studiot

[druS]

1 hour ago, studiot said:

1 hour ago, studiot said:

 

Would you agree with the first line then?

 

 

One of the characteristics of resonance structures is the change in bond length from the formative resonance structures.

But it does IMHO show Hannoe has not properly distinguished between atomic orbitals, hybrids orbital, molecular orbitals (and says so her/his self).

 

I was just waiting for more questions from the OP about what I said.

 

There have been too many instances just lately where a question was asked and I or others put significant effort into an answer for an OP who never came back.

 

It is, however, a good subject for discussion that may also benefit others.

studiot, I doubt I am the only one who wont miss your posts. Plenty goes over my head, but I learn a little bit every time. It is never imo wasted effort.

 

[StringJunky]

47 minutes ago, druS said:

studiot, I doubt I am the only one who wont miss your posts. Plenty goes over my head, but I learn a little bit every time. It is never imo wasted effort.

One is not writing just for contemporary readers but those in the future as well: forums are repositories.

[hypervalent_iodine]

2 hours ago, studiot said:

 

Would you agree with the first line then?

 

 

One of the characteristics of resonance structures is the change in bond length from the formative resonance structures.

But it does IMHO show Hannoe has not properly distinguished between atomic orbitals, hybrids orbital, molecular orbitals (and says so her/his self).

 

I was just waiting for more questions from the OP about what I said.

 

There have been too many instances just lately where a question was asked and I or others put significant effort into an answer for an OP who never came back.

 

It is, however, a good subject for discussion that may also benefit others.

 

I am not sure I follow the point of your bond length statement. While true, I don’t see it’s relevance to mine or the OP’s post. They didn’t mention bond length?

I should say that I found the OP difficult to decipher, so I may well be misunderstanding them myself. I agree the OP seems to be mashing several different models and getting a little lost (understandable, it gets confusing), but the thrust of what they’ve taken out of it (from their final paragraph) reads okay. I think some clarification from the OP would be nice. Perhaps they are just not very articulate. I would like to know exactly what is meant by hybrid resonance orbital, for instance. 

 

 

 

[studiot]

4 hours ago, hypervalent_iodine said:

 

I am not sure I follow the point of your bond length statement. While true, I don’t see it’s relevance to mine or the OP’s post. They didn’t mention bond length?

I should say that I found the OP difficult to decipher, so I may well be misunderstanding them myself. I agree the OP seems to be mashing several different models and getting a little lost (understandable, it gets confusing), but the thrust of what they’ve taken out of it (from their final paragraph) reads okay. I think some clarification from the OP would be nice. Perhaps they are just not very articulate. I would like to know exactly what is meant by hybrid resonance orbital, for instance. 

 

 

 

 

Ok so my beef with the first line of the OP is shown in my Fig 1

It is clearly wrong to state that the  resonance orbital, hybrid or not, doesn't represent actuality.

The above two Kekule primitive structures for benzene show alternate double and single bonds, but neither can be isolated from a flask of benzene, because neither actually exist.
In fact all the bonds appear identical (with length 1.4A rather than the 1.5+A for a carbon-carbon single bond or 1.3A for a double).

So the bonds as diplaced in the 'resonating' structures do not exist, but bonds which have a character which is a mixture of both do.

 

The problem with the summary is this

On 24/06/2018 at 8:12 AM, hannoe said:

Meaning, the electron pairs that can move around can be only in pi-bonds and AO-s just like in resonance structures.

The electron pairs need not be only in Pi bonds as stated.

My Fig 2 shows clearly that the resonating structures in carbon dioxide have both polar and non polar characteristics. Two have in fact charge separation by transfer of electrons.

 

 

I think it will take at least one substantial post, starting at the beginning, to put all this right and explain it properly.

 

So hannoe, speak up for yourself, and please tell us if English is not your first language so we can adjust for that.

Edited June 25, 2018 by studiot

[hannoe]

Thanks for your replies! Obviously I had mixed some concepts up so I went over them again and it's more clear now. 

I got the answer that I was looking for (thanks studiot!) - my question was about whether the resonance structures are just changing between each other very quickly or it is actually an average of the resonances. As I understand now the second one is correct. Meaning actually new orbitals form (or the orbitals take a significantly different shape) that have lower energy than the usual molecular orbitals.

[studiot]

44 minutes ago, hannoe said:

Thanks for your replies! Obviously I had mixed some concepts up so I went over them again and it's more clear now. 

I got the answer that I was looking for (thanks studiot!) - my question was about whether the resonance structures are just changing between each other very quickly or it is actually an average of the resonances. As I understand now the second one is correct. Meaning actually new orbitals form (or the orbitals take a significantly different shape) that have lower energy than the usual molecular orbitals.

Thanks for the answer, that clears up a lot.

 

 

You should be aware of and beware of the phenomenon of tautomerism where there is actually a mixture of two structural forms with the same raw formula.

The example in the sketch is for acetoacetic ester which exists as a mixture of the two forms which can be isolated.

Once isolated the resultant fairly quickly degrades back to the mixture proportions (correct at room temperature).

 

 

This is not resonance so it is easy to mix them up.

 

Feel free to ask for more detail.

 

Edited June 25, 2018 by studiot

[hypervalent_iodine]

7 hours ago, hannoe said:

Thanks for your replies! Obviously I had mixed some concepts up so I went over them again and it's more clear now. 

I got the answer that I was looking for (thanks studiot!) - my question was about whether the resonance structures are just changing between each other very quickly or it is actually an average of the resonances. As I understand now the second one is correct. Meaning actually new orbitals form (or the orbitals take a significantly different shape) that have lower energy than the usual molecular orbitals.

 

You might like to read these: 

http://www.science.oregonstate.edu/~gablek/CH334/Chapter1/resonance_MO.htm 

https://chem.libretexts.org/LibreTexts/Mount_Royal_University/Chem_1201/Unit_4%3A_Chemical_Bonding_II_-_Advanced_Bonding_Theories/4.11%3A_Multiple_Bonds_in_MO_Theory#Molecular_Orbitals_and_Resonance_Structures

https://www.masterorganicchemistry.com/2017/01/24/conjugation-and-resonance/

 

7 hours ago, studiot said:

 

Ok so my beef with the first line of the OP is shown in my Fig 1

It is clearly wrong to state that the  resonance orbital, hybrid or not, doesn't represent actuality.

The above two Kekule primitive structures for benzene show alternate double and single bonds, but neither can be isolated from a flask of benzene, because neither actually exist.
In fact all the bonds appear identical (with length 1.4A rather than the 1.5+A for a carbon-carbon single bond or 1.3A for a double).

So the bonds as diplaced in the 'resonating' structures do not exist, but bonds which have a character which is a mixture of both do.

 

The problem with the summary is this

The electron pairs need not be only in Pi bonds as stated.

My Fig 2 shows clearly that the resonating structures in carbon dioxide have both polar and non polar characteristics. Two have in fact charge separation by transfer of electrons.

 

 

I think it will take at least one substantial post, starting at the beginning, to put all this right and explain it properly.

 

So hannoe, speak up for yourself, and please tell us if English is not your first language so we can adjust for that.

You do realise they said pi bonds and atomic orbitals, not just pi bonds? Granted, it's still not complete. Hybridised orbitals containing lone pairs or radicals may also contribute.