Hi there,

I was wondering if there is a quick and easy way to assign an R or S configuration to a chiral enantiomer instead of either setting the lowest priority molecule back into the plane, or having to physically build the model using a modelling kit. Also, is there any quick way to identify a meso compound?

Thanks.

PS Am I correct in saying that the top left compound is an R-entantiomer whereas it's mirror image is an S-enantiomer?

 

 

Edited December 19, 201015 yr by hypnotiq

As far as I'm aware, there is no other way to assign R/S to structures becasue the R/S notation comes from giving the substituents there ordering priorities. I don't build models for organic stereocentres, its just practise of being able to rotate the object in my head in 3D...just practise. A meso compound is one that contains stereogenic centres, but also contains an internal plain of symmetry....so if you can spot a plane of symmetry, then you have a meso compound.

 

If one enantiomer is R, then by definition, the other has to be S. IN this case, the iodine has highest priority, followed by bromine, chlorine and finally hydrogen. Rotate the molecule so that the hydrogen is pointing away from you; the priorities are then going clockiwise so the top left is indeed R.