4.4 Cycloalkanes and Cyclohexane Chair Conformations

Chad explains how to draw cyclohexane chair conformations and distinguishes between axial vs equatorial positions and descries 1,3-diaxial interactions.
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[@aksharpokala3260]

Hey Chad, would there be steric strain between the 1 and 4 carbon in a cyclohexane if there was a methyl group or bigger in those areas? I'm getting a little confused on the intricacies of steric strain.

[@stephaniegallegos1715]

Hi Chad, for 1,3 diaxial interactions what do you mean by "larger groups"?

[@ChadsPrep]

Hello Stephanie! I mean one of two things. The first is anything larger than hydrogen will experience 1,3-diaxial interactions. But the second thing I mean is the larger the group the higher the energy as a result of these 1,3-diaxial interactions. So having an ethyl group in an axial position would be higher energy than having a methyl group in an axial position. Hope this helps!

[@jigarpatel9912]

Hi Chad, quick question. In a trans cyclohexane, does wedge always have to be up while a dash has to be down?

[@ChadsPrep]

Jigar, technically no. But you can get yourself into trouble rotating the molecule around and for chiral cyclohexanes you might accidentally come up with the enantiomer of the molecule you're trying to draw. Which is why I stick with the rule of always making the wedges point up and the dashes point down. If you want to rotate the molecular after that 180 degrees out of the plan that is up to you, but it can be a little tricky to try to draw it that way from the get go. Hope this helps!

[@viralload7086]

wait, so we just flip the chair and the energy levels are not the same anymore? i thought it was just like seeing it from another point of view

[@ChadsPrep]

Not necessarily. For certain symmetrical cyclohexanes such as cis-1,2-dimethylcyclohexane the two chair conformations would be equal in energy, but for the majority of examples the two chair conformations would not be equal in energy and therefore not equally present in solution. Generally, when the larger substituents and/or the greater number of substituents are in equatorial positions the more stable and lower energy. Hope this helps!