R and S for chair??

[tRNA]

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does anyone know how to assign R and S to chair conformations,
i know how to do that for fisher, numan, and any open chain, but i don't know how to do it for chair, i made a model but it's still kinda hard to tell for some carbons which bond is coming towards/away from you from the drawing on paper...any ideas??
is that likely to be on the test?
thanks

 

[predentlsu1]

I dont think you will have to determine R/S on a chair.......that is a little complicated for this test. If they ask you an R/S question it will more than likely be from a linear molecule.......If they ask you a stereochemistry question about a chair it would more than likely involve cis/trans rather than R/S. Other chair questions they could ask would be to correctly position axial and equitorial groups or to determine which chair is the most stable.

But just incase......to determine R/S stereochemistry for a chair it is often easier to convert the chair to a 2 dimensional model with cis/trans indication and then figure out R/S.