Bezene

[muskan]

if we shift all double bonds of benzene to one side, what will be the effect on the its stability?

[Area54]

In the hope of prompting a more knowledgable answer here are a couple of thoughts:

The double bonds could not be shifted to one side since this would conflict with the valence of Carbon.

I understand double bonds are an older concept that has been replaced, in this instance, by delocalised electron distribution. wikipedia has something to say on the matter.

[BabcockHall]

@OP, One can write two resonance forms for benzene, both of which contribute equally to the true structure, which is a hybrid (blend).

[studiot]

15 hours ago, muskan said:

if we shift all double bonds of benzene to one side, what will be the effect on the its stability?

It's not clear to me what you mean by this. You can't just move the double bonds without also moving the single bonds.

Look at my diagrams.

If we start with a standard representation of the first double bond on AB and follow round we get figure 1 Note that every carbon is attached to a single hydrogen.

If we move every bond round the ring one place so the double bond AB moves to BC and the single bond BC moves to CD etc we get fig 2.

If instead we swop AB with AF and CD with DE we move  the single bonds the other way we will have all the double bonds on one side and all the single bonds on the other, as in figure 3.
However will also have to move some of the hydrogens, though we will still have the right number of bonds for C₆H6, two of the carbons 2 hydrogens and 2 will have one apiece.

So tell us what you mean so that your question can be properly answered.

[hypervalent_iodine]

6 hours ago, Area54 said:

In the hope of prompting a more knowledgable answer here are a couple of thoughts:

The double bonds could not be shifted to one side since this would conflict with the valence of Carbon.

I understand double bonds are an older concept that has been replaced, in this instance, by delocalised electron distribution. wikipedia has something to say on the matter.

 

...what?

[Area54]

13 hours ago, hypervalent_iodine said:

 

...what?

1. No one had responded to the plea for help, so I summed up my recollection of chemistry from many decades ago and offered my take on it.

2. I opened with a statement concerning the primary purpose of the post, namely, to prompt a more knowledgable answer.

3. It's disappointing you chose not react to the prompt, but instead chose to highlight that what I wrote was incorrect in some way - a caveat already covered in my opening sentence.

4. On the the off chance that the OP is still looking for an informed answer would you like to help them out with that now?

[hypervalent_iodine]

5 hours ago, Area54 said:

1. No one had responded to the plea for help, so I summed up my recollection of chemistry from many decades ago and offered my take on it.

2. I opened with a statement concerning the primary purpose of the post, namely, to prompt a more knowledgable answer.

3. It's disappointing you chose not react to the prompt, but instead chose to highlight that what I wrote was incorrect in some way - a caveat already covered in my opening sentence.

4. On the the off chance that the OP is still looking for an informed answer would you like to help them out with that now?

 

I chose not to because other's have given plenty of good starting points. There's not a lot I can add that wouldn't be simply answering the question. I did feel it prudent to ask for you to clarify your post however, as I for one couldn't make any sense of it, and I felt it could be especially confusing for the OP. 

[Area54]

15 hours ago, hypervalent_iodine said:

 

I chose not to because other's have given plenty of good starting points. There's not a lot I can add that wouldn't be simply answering the question. I did feel it prudent to ask for you to clarify your post however, as I for one couldn't make any sense of it, and I felt it could be especially confusing for the OP. 

Fair enough.

I made this statement: The double bonds could not be shifted to one side since this would conflict with the valence of Carbon .

That was my way of expressing what Studiot said in his post, which he summarised as " You can't just move the double bonds without also moving the single bonds." Carbon has a valency of 4. If we shift the double bonds and try to keep the hydrogens where they are it simply cannot work - which is what we are both saying. I accept that this was not clear, though I can't quite see why not.

I then made this statement: I understand double bonds are an older concept that has been replaced, in this instance, by delocalised electron distribution. wikipedia has something to say on the matter.

I would welcome, for my own education, an explanation of what is incorrect in that statement. Thanks.

[hypervalent_iodine]

On 10/01/2018 at 10:47 PM, Area54 said:

Fair enough.

I made this statement: The double bonds could not be shifted to one side since this would conflict with the valence of Carbon .

That was my way of expressing what Studiot said in his post, which he summarised as " You can't just move the double bonds without also moving the single bonds." Carbon has a valency of 4. If we shift the double bonds and try to keep the hydrogens where they are it simply cannot work - which is what we are both saying. I accept that this was not clear, though I can't quite see why not.

I then made this statement: I understand double bonds are an older concept that has been replaced, in this instance, by delocalised electron distribution. wikipedia has something to say on the matter.

I would welcome, for my own education, an explanation of what is incorrect in that statement. Thanks.

 

I have a problem with describing it as single bonds moving around. I didn't spot that in studiot's post, but I take issue with it there also. It's a misrepresentation of what happens, and doesn't follow from the question in the OP, hence being a possible source of confusion. At no point do the single bonds move. Only the double bonds. And it absolutely does work. If it helps, this is more or less what the OP is describing:

 

I also did not understand what you meant when you said that double bonds were outdated. Since when was that true? 

[Area54]

Thank you for your reply. I don't see how the diagram you have offered showing the double bond movement reflects the OP's question. I interpret "shifting all the double bonds of benzene to one side" to mean this. That was the basis for my response.

 

My remarks on the outdated concept of double bonds was based upon poorly remembered concepts of orbitals from an undergaduate Chemistry course in the 1960s and a misreading of the wikipedia article. I believe I am correct in stating that the benzene structure does not contain "conventional" double bonds.

[hypervalent_iodine]

2 hours ago, Area54 said:

Thank you for your reply. I don't see how the diagram you have offered showing the double bond movement reflects the OP's question. I interpret "shifting all the double bonds of benzene to one side" to mean this. That was the basis for my response.

 

My remarks on the outdated concept of double bonds was based upon poorly remembered concepts of orbitals from an undergaduate Chemistry course in the 1960s and a misreading of the wikipedia article. I believe I am correct in stating that the benzene structure does not contain "conventional" double bonds.

 

Right, I see. I interpreted it in the way I did based on what students are normally learning about regarding benzene and the movement of double bonds. I can see where your impression of the OP comes from, though I think that the question is designed to prompt thinking about resonance more than anything else. I'm not sure I see much of a place for discussing the structure you have drawn in any lower level chemistry course that would clearly illustrate anything they might be learning (double bond stability is normally taught in terms of substitution and E/Z configuration). That is just my opinion, albeit mildly informed from my own teaching experience. Of course, one should not underestimate the capacity for institutions to teach simple concepts in bizarre and convoluted ways. We'll never really know unless the OP comes back. 

Regarding your last comment, you are correct that they aren't thought of as isolated, "conventional," double bonds.