Cis/Trans- Cyclohexane

[osimsDDS]

Question on cis and trans cyclohexanes:

If you have a cis cyclohexane both substituents will be on equitorial or axial or vis versa.
If you have trans cyclohexane both substituents will either be in equitorial or axial....

Does this occur with 1,3 and 1,4 or does this differ for each.

Also I heard that halogens only do axial??? is this true...thanks

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[userah]

for cyclohexanes, first draw out the chair confirmation. i believe it does depend on whether its 1,3 or 1,4 because you are trying to minimize steric effects. so for 1,4 trans it will be equitorial but if you have 1,3 trans one will be on equitorial and other will be on axial. for cis, it would be the opposite. for 1,4 cis one will be equitorial and other will be axial and for 1,3 cis, they will both be equitorial. (if you draw out the chair, and follow along it might be easier) as for which one would be equitorial and which one would be axial for 1,4 cis and 1,3 trans, depends on the groups attached. whichever is more sterically hindered will take the equitorial.

im pretty sure this is right but it has been over a month since my dat and i havent looked at book since haha but no one was replying to the thread so i thought id give it a whirl. hopefully someone will confirm or debunk this explanation?

yes i believe halogens only do axial.

 

[klutzy1987]

Question on cis and trans cyclohexanes:

If you have a cis cyclohexane both substituents will be on equitorial or axial or vis versa.
If you have trans cyclohexane both substituents will either be in equitorial or axial....

Does this occur with 1,3 and 1,4 or does this differ for each.

Also I heard that halogens only do axial??? is this true...thanks

For 1,4 cyclohexane and any even numbers for that matter you will want the cyclohexane to be in trans. That way both substituents will be in the equatorial position. For 1,3 and any other odd numbers you want it to be in cis so that that way both may be in equatorial at the same time.

 

[klutzy1987]

In regrards to halogens when yu want to eliminate a Halogen and a Hydrogen to make a double bond you need both the halogen and the Hydrogen to be eliminated to be in the axial position. The reason for this is because the elimination happens syn and both of the substituents have to be lined up in the same plane.

 

[gentile1225]

cis and trans does not necessarily mean that either both groups are equatorial/axial or that one is equatorial and the other axial, it simply refers to the position of the substituent in relation to the hydrogen at that carbon. so if 1,2-dimethylcyclohexane were cis then one methyl group would be equatorial and the other axial.

in the case of halogens, they are most stable in the axial position. with any cis/trans problem always draw the chair conformation.