Assigning absolute configurations

[shefv]

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I learnt in my organic chemistry course that when the lowest priority group is not facing away from you, assign the configuration as normal and take the opposite of that. I am using the method on some sample practice but my answer is not correct according to the solution.

How do we assign absolute configuration when the lowest priority group is not facing away? can someone please go over the practice questions and discuss this concept.

Thanks!

 

[Cawolf]

The rule of swapping only applies if the lowest priority group is facing out of the paper (wedge).

I personally like to simplify the stereocenters by changing the groups to configurations, then rotating the molecule so the lowest priority is into the paper (dash). This takes 10 seconds longer, but applies to any situation. It is most useful when the lowest priority group is not a wedge or dash.

 

[shefv]

Thanks 🙂

 

[Labrat07]

Dang, this is tough for me. I used to do normal and change configuration as well. For this technique you have to see it in 3d with your mind.

 

[Cawolf]

@Labrat07

Not if you write it down on paper.

I am poor at visualizing and all I had to teach myself was how the position of the groups change relative to each other.

 

[Labrat07]

That's true. I'll practice on this. Thanks, Cawolf.