Chirality/Stereochemistry Video Series: Video 4
R and S configurations are pretty straight-forward when priority group #4 is conveniently in the back of the molecule. There’s even a quick trick for when group #4 is forward (as taught in this video).
But what happens when priority group #4 is in the plain of the page? Do you treat it as a rear group, forward group?
Many professors will teach you to build a model kit (hint: don’t rely on your model kit) or mentally rotate and redraw the molecule placing group #4 in the back
OUCH! Not only are these methods a waste of time, they introduce too much stress and confusion on exams. My swap method taught below is tricky to learn at first. BUT… once you get it I GUARANTEE you’ll find yourself saving 5, 10, even 15 minutes on your stereochemistry exam questions.
(Watch on YouTube: Swap. Click cc on bottom right for video transcription.)