3R-ethyl-trans-decalin (what would it look like)

[UIUCstudent]

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The trans part is throwing me off. Would 3R-ethyl-trans-decalin and 3S-ethyl-trans-decalin be considered enantiomers?

 

[tttgo]

I'll try my best to answer. First look up decalin on wikipedia. I numbered my decalin based on their image. Now look at their first image with the chair conformation of trans decalin. Let's attach the ethyl on position 3 equatorial. I think that makes it R. It changes to S when you attach it axial. If you number the molecule differently though, like starting 1 on bottom left, it might not be true, but I'm not sure. I'm having a hard time picturing the 3D rotation, but the S form from numbering differently might be imposable on the R form. Anyone else have an idea?

 

[tttgo]

Oh, I see. I was thinking that you could somehow number differently (have the ethyl on top right), but I didn't see the two bridge hydrogens. Thanks for the explanation.

 

[Rolling]

The only way they would be enantiomers is if they were no other chiral centers. The two carbons that are a part of both rings are chiral (4 different substituents). So keeping the configuration the same for every other part of the molecule, you can see they would just be diastereomers.