# R and S Configuration Understanding

So I have been trying to understand how to draw R and S configurations. I feel like I have understood how to draw them, but every time I do a question, I get a wrong answer.

So here is what I have understood,

1. The lowest priority goes to the back of the compound meaning on the dash line.
2. The highest priority is on the top.
3. You can play around with the 3rd and 4rth, so that one is on the 'out of page' and the other is on the line, so that you can differentiate between the R and S.

But then there is this picture for example from my book,

I have been going crazy trying to understand it. The things I do not understand are these,

1) I understand the diagrams on the right side. That I have been doing as well

2) But then when we look at the diagrams on the left. The configuration is completely opposite. Even though it says S, the configuration is like of a R. Plus the highest one is going into the page and not the hydrogen. WHY? It is driving me crazy because they do that for all the examples. When they S, they actually make an R and vice versa. Whereas on the internet it is a different story. So I really need someone to tell me what I should do.

• You just need to rotate the structure on the left to make the H go back into the plane of the page. It takes a bit of getting used to at first, and making a model can be extremely helpful, but eventually you'll get there. Good luck! Aug 17, 2016 at 22:44
• You are confused because in the left diagrams, the low-priority atom (Hydrogen) stands up: it's not on the back of the molecule! To explain the first model, you have CH2OH coming towards you, OH going away from you, and CHO and H at the same distance from you. You should imagine yourself looking at the molecule from another perspective: if you look at it from the bottom, you have hydrogen away from you, and the other groups at the same distance from you, in a triangle shape (that's the right diagram!). Remember: the low priority atom should always stay away from you.
– user32223
Aug 17, 2016 at 23:08
• Transcribing chiral structures is invariably going to cause misassignments. Here is my advice: chemistry.stackexchange.com/questions/99721/… Sep 20, 2021 at 2:02