O chem question

[alanan84]

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When converting cylcohexane into a chair conformation, how do we know which substituents will be axial and which ones will be equatorial?

 

[Chesnok]

Ones that are axial will be equatorial, and vise versa

 

[Danny289]

When converting cylcohexane into a chair conformation, how do we know which substituents will be axial and which ones will be equatorial?

it deponds to the question and what they are asking. just remeber when substitution are equatorial, it is more stable and least energy. In general more stable substitutions are favoured.

 

[alanan84]

Well lets say your just given the planar molecule of 1,2-dimethylcyclohexane and they ask for the answer in the chair conformation. How would you know which ones would be axial and which ones would be equatorial? Does that make sense?

 

[alanan84]

it deponds to the question and what they are asking. just remeber when substitution are equatorial, it is more stable and least energy. In general more stable substitutions are favoured.

So you would just put them both equatorial?

 

[Chesnok]

Just read what I posted it and add word initially
I f you see sustituents axial initially (before conversion) , you should draw/see it being equatorial. It's that simple.

 

[mistero]

if they just give you the name of the molecule or in a non chair formation, it depends whether it is cis or not. Since the methyls are right next to each other, if it is cis, one is axial and one is equatorial and if they are trans, they will either be both equatorial (more stable) or both axial.

 

[Contach]

if they just give you the name of the molecule or in a non chair formation, it depends whether it is cis or not. Since the methyls are right next to each other, if it is cis, one is axial and one is equatorial and if they are trans, they will either be both equatorial (more stable) or both axial.

I think what Mistero is saying is what the OP wanted. Don't listen to chesnok, I think he misinterpreted what the question was.

mistero said:
if the two substituents are next to each other, and cis-configured, then one will be axial and one will be equatorial. or equatorial and axial if a ring-flip occurs
now I want to add:
if the two substituents are one carbon apart from each other and cis-configured, both will be either axial or if a ring flip occurs both will be equatorial.

Once again, a diagram would do wonders to help.. but I am too lazy - sorry.

 

[doc3232]

Firstly, to the OP, your answer is very complicated and depends on every molecule.
Equatorial is NOT always more stable. Imagine putting two Chlorines next to each other both equatorial positions. Do not forget why we equatorial is usually more stable. Repulsion from 1,3 diaxial positions between the Axial hydrogens and the added substituents (in this case Chlorines). The tiny amount of repulsion between the H and the Cl in axial positions is nothing compared to the instability of 2 chlorines next to each other in equatorial positions...It is hard to explain, but I hope I helped.

 

[soopasteve]

a general rule of thumb is as follows:

when looking at a flattened ring (being careful to make sure that you have it drawn so that you can see whats pointing up and whats pointing down) label the largest substituent as equatorial. then go around the ring and label the remaining substituents and hydrogens in alternating order. AKA if you go one to the left of the first equatorial group, the next one is axial, then equatorial again, then axial again, etc.

ps - 3d model kits are awesome for helping out with this.

 

[alanan84]

I think what Mistero is saying is what the OP wanted. Don't listen to chesnok, I think he misinterpreted what the question was.

mistero said:
if the two substituents are next to each other, and cis-configured, then one will be axial and one will be equatorial. or equatorial and axial if a ring-flip occurs
now I want to add:
if the two substituents are one carbon apart from each other and cis-configured, both will be either axial or if a ring flip occurs both will be equatorial.

Once again, a diagram would do wonders to help.. but I am too lazy - sorry.

Yeah I think you and mistero understood what I was trying to say here, and yeah I diagram would be nice. So if they are next to each other and cis, then one will be axial and one equatorial. If they are next to each other and trans, they will both be either axial or equatorial. And if they are one carbon apart and cis, one will be axial and one equatorial. Is that correct?

I ask because I believe I've gone through a question like this on both topscore and destroyer and got it wrong because I thought if they were cis then they'd both be equatorial or axial for that matter. But what yall are saying matches the answers so I feel much better. Thanks to all those you have helped me on this one!

 

[alanan84]

a general rule of thumb is as follows:

when looking at a flattened ring (being careful to make sure that you have it drawn so that you can see whats pointing up and whats pointing down) label the largest substituent as equatorial. then go around the ring and label the remaining substituents and hydrogens in alternating order. AKA if you go one to the left of the first equatorial group, the next one is axial, then equatorial again, then axial again, etc.

ps - 3d model kits are awesome for helping out with this.

By the way, I now see what you're saying and that helps too!

 

[Contach]

Yeah I think you and mistero understood what I was trying to say here, and yeah I diagram would be nice. So if they are next to each other and cis, then one will be axial and one equatorial. If they are next to each other and trans, they will both be either axial or equatorial. And if they are one carbon apart and cis, one will be axial and one equatorial. Is that correct?

I ask because I believe I've gone through a question like this on both topscore and destroyer and got it wrong because I thought if they were cis then they'd both be equatorial or axial for that matter. But what yall are saying matches the answers so I feel much better. Thanks to all those you have helped me on this one!

perfect you got it! and no1 had to draw any diagrams 😍

 

[mistero]

Check the question again, which one was it?
it might be that it asked for an elimination, which only happens when the H and the other molecule that is being eliminated are both axial. In that case, you put the largest molecule in equatorial position and the atoms that are supposed to be eliminated should be axial, not equatorial.