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

Be consistent when redrawing the molecule with the original drawing. Don't draw the wedged bond on the top of the molecule if it was on bottom in the original drawing. Hopefully this helped, this is a confusing subject though and like I said earlier it's difficult to explain even in person. I would definitely recommend getting a set of ball and stick models as it makes visualization much easier. Practice enough and you'll get to where you dont need them anymore.

By the way to clear up any confusion, this step-by-step is essentially rotating the molecule (you aren't changing the structure or stereochemistry). I simply laid out detailed directions so that if you were having difficulties visualizing rotating the molecule in your head, you wouldn't have to think about it. As long as you follow the directions and rules I have laid out, it should result in a new drawing of the original molecule from a different angle, the angle in which the lowest priority group is in the dashed (going away from you) position

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.

Use the simulation linked below to go back and forth between the priority 4 substituent on the top (OPs left panels) and behind the plane of the display (OPs middle panel).

http://proteopedia.org/wiki/index.php/R/S_nomenclature

It is like looking at a clock from behind. If you look from the front, clocks go clockwise, but if you look from the back (and the clock is translucent), if goes counterclockwise. That is why it is important to correctly orient the priority 4 substituent before determining R vs. S.

The lines are on vertical positions of Fischer projection. CHO is at the bottom of the vertical line, and it seems to be on the right side.So, the dashed line is on the left side of the horizontal position and the solid wedge on the right side. Now, draw Fischer projection as such. H is up CHO is down on vertical axis. CH2O right and OH is left on horizonatal line. Select priorities. Priorities are shown in the figure as numbers from 1 to 3. The chiral carbon has S configuration. This is according to my knowledge without being responsible if there is something wrong in my answer. Better check with your teacher.

• The drawing in the question are not Fisher projections, so how is this relevant? Feb 23 at 13:38