How to Assign R and S Configurations Without a Molecular Model

Chiral centers come in two flavours - vanilla or chocolate chip... Just kidding! They come in R and S varieties. There's a three-step process for assigning the R or S, and one of the steps in putting the lowest priority group at the back, away from you. But what do you do when the lowest priority group isn't behaving and isn't already at the back? Read on and watch the video to find out two simple strategies that will rock your chiral world!

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What happens when the hydrogen doesn't behave?

In the video below, I briefly recap the rules for assigning R and S. But, the focus of the video is two rule-based approaches to assigning the absolute configuration of a chiral center when the lowest priority group is not behaving, and not already at the back. It's normally a hydrogen - you know you can't trust those little rascals!

An R and S configuration trick?

I hate the saying anything is a trick, but if this works for you, then call it what you will! 😉

Good luck, and let me know how you're going with and S in the comments below!

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Mark Coster

About the Author

Mark Coster

The 'team' is Dr. Mark Coster. :) Mark makes stuff. When he’s not making stuff, he’s teaching other people how to make stuff. Mark was one of those kids who loved nothing more than to build things out of Lego. He still feels that joy, but now his ‘stuff’ is molecules that he builds from atoms. He occasionally writes biographies in third person. ;) And he still likes Lego too. Organic Chemistry Explained

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