TBR Orgo Ex: 3.9

[discowisco]

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I dont see how both molecules are Enantiomers. The way I check for enantiomers is the R and S method. The first molecule on the left is S , R while the one on the right is S, S. This makes them diasteromers???

 

[Jepstein30]

I dont see how both molecules are Enantiomers. The way I check for enantiomers is the R and S method. The first molecule on the left is S , R while the one on the right is S, S. This makes them diasteromers???

post a picture (or at least the molecule names) so those without the book can help you?

 

[discowisco]

http://tinypic.com/r/ztxl01/6

 

[Jepstein30]

http://tinypic.com/r/ztxl01/6

Ah ok, well you did figure out the R/S part correctly. Which is good because that's really the more complicated part. Be sure you are using the trick for when the hydrogen isn't in the back to save some time.

Enantiomers have ALL stereocenters flipped. Diasteromers have NOT ALL (could range from just 1 site flipped to all but 1 flipped) sites flipped.

So in these molecules, you have S-R and S-S. Of the two stereogenic sites, only one was flipped (the second one). Therefore, these are diasteromers. To make the enantiomer of the molecule on the left, you'd have to redraw the molecule to be R-S. Likewise, the enantiomer of the molecule on the right would be R-R.

 

[discowisco]

haha I think they are diasteromers too, Im asking why the book says its enantiomers.

 

[Jepstein30]

haha I think they are diasteromers too, Im asking why the book says its enantiomers.

They're wrong 😉

Look for an online errata. What edition of the book are you using? I have the newest set around here somewhere and can check later for you.