cis/trans isomers

[sdb09]

Can someone please explain to me why both of these molecules above would be trans-isomers. I keep confusing myself when I have to figure out cis/trans isomers on cyclohexane.



I thought they would both be cis and don't understand why they are both trans.

Thanks!

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[mosquitoman]

this one is easy.. they are both pointed differently... if they were both pointed same way [up/up or down/down] they would be cis

try drawing in the hydrogens so it will make more sense to you

 

[Ninjaface]

I thought they would both be cis and don't understand why they are both trans.

Well, for one they are the exact same molecules (flipped 180), and any substituents that are in the same position (i.e. both equatorial or both axial) must be cis to each other, but they (the methyl groups here) are not, and thus are trans by default.

 

[sdb09]

Ok that makes a bit more sense...though when I tried to apply that to this molecule:

It is trans - but I thought that if every other substituent was axial (like above where they are the same) it would be cis??

 

[AZFutureDoc]

No, if 2 adjacent carbon's have F.G.'s in the equitorial position, they will always be trans to each other.

 

[sdb09]

No, if 2 adjacent carbon's have F.G.'s in the equitorial position, they will always be trans to each other.

Are you talking about the second picture I posted (Compound E)? I'm sorry I'm still confused - there aren't 2 adjacent carbons w/functional groups..they skip a carbon which is why I thought it was trans.