5.2 How to Assign R and S | Absolute Configuration | Organic Chemistry
In this lesson on stereochemistry, Chad comprehensively covers how to assign R and S to chiral centers using the Cahn-Ingold-Prelog rules and works several R and S configuration practice problems throughout the lesson. He begins with a simpler example and shows how to assign R and S to a chiral center in 3 different scenarios:
1) When the lowest priority group has a dashed bond
2) When the lowest priority group has a wedged bond
3) When the lowest priority group has a bond in the plane
Chad then moves on to covering trickier examples showing how to assign priorities for R and S when the same atom is attached to the chiral center. He describes how you move down the chain organizing each attached atom by what additional atoms it is attached to until a point of difference is found. Chad covers a couple of trickier examples involving this and involving how to assign priorities in molecules having double or triple bonds. Finally, he concludes the lesson by showing how to name compounds having chiral centers.
If you want all my study guides, quizzes, and practice exams, check out my premium course at www.chadsprep.com/organic-che...
00:00 Lesson Introduction
01:00 Introduction to the Cahn-Ingold-Prelog Rules for Assigning R and S to Chiral Centers
04:46 Assigning R and S when the Lowest Priority Group has a Wedged Bond
06:15 Assigning R and S when the Lowest Priority Group has a Bond in the Plane
10:25 Breaking the Tie: More Complicated Example of Assigning R and S
13:33 Assigning R and S Configuration with Double Bonds or Triple Bonds
18:48 Naming Molecules with Chiral Centers
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You really deserve so much more recognition!! Your videos are amazing and never fail to help. Please keep doing what you're doing!
@ChadsPrep
3 жыл бұрын
Thank you for your comment and praise, Alexander.
"Or if you just feel sorry for short bald guys" LOL! Thank you for uploading these videos Chad, you make chemistry so easy to understand!
@ChadsPrep
Жыл бұрын
You're welcome and Thank You!
God bless you honestly. i have never understood these concepts with such clarity as someone who has been struggling through two years of ochem, but here you are like a divine gift. thank you for all you do!
@ChadsPrep
Жыл бұрын
You're welcome - Happy Studying!
Chad you actually make science so enjoyable! I was so nervous going into o-chem this semester but ever since I found your channel I've been falling in love with the subject and how you explain things so nicely! Super grateful
@ChadsPrep
3 жыл бұрын
Thank you, Sara - and good luck with your ochem - glad you are finding the videos so helpful!
This was such a great video! Made it so easy to understand, love this Organic Chemistry Playlist! :D
@ChadsPrep
Жыл бұрын
Glad you found us!
Your videos are a great supplement to my course. Thanks!
@ChadsPrep
3 жыл бұрын
You're welcome Joey! Glad you're finding them helpful!
You are the best teacher I have ever had. You are truly a blessing. I've made A's in all my gen chem and gen physics classes because of you. I'm sure I'll be able to do the same in ochem this summer with your help. Thank you so much!!!!
@ChadsPrep
2 жыл бұрын
That is fantastic, Chloe - keep up the good work!
you made me understand all the ochem topics in a week😭❤️ THANK YOU SO MUCH!!!!
@ChadsPrep
5 ай бұрын
Glad I could help!
I have learned alot about isomers from your first two videos and I thought I should comment because You are an awesome teacher you explain everything clearly. Thank you for coming up with chads prep it has helped me a lot! you make me want to pursue a career in chemistry keep this up its excellent!
@ChadsPrep
2 жыл бұрын
Thank you for saying so, fana jafer.
currently taking o-chem and your videos are so helpful! thank you
@ChadsPrep
3 жыл бұрын
Glad you found us, Danait - good luck with o-chem and your studies!
Excellent! Thank you. The best explanation, anywhere. You are the best!
@ChadsPrep
Жыл бұрын
You're welcome - Thank you!
Thank you so much! You explained this concept in such an easy to understand way!
@ChadsPrep
8 ай бұрын
You're welcome and Thank You.
As always, thank you so much!
@ChadsPrep
2 жыл бұрын
You are welcome, Timothy!
You're a great teacher. I hope you are aware of all the good that you do. I hope you acquire everything you deserve 😊
@ChadsPrep
8 ай бұрын
Thanks - always appreciate the kind words.
Thank you so much. You're helping out a lot of students including me. Please keep doing what you're doing.
@ChadsPrep
Жыл бұрын
You're welcome - Thank You.
Thanks, this makes a lot more sense now. Glad u can also admit that profs often give much more challenging questions on exams than in practice.
@ChadsPrep
5 ай бұрын
You're welcome and Thank You.
Hi Chad! I was wondering if you had any study guides for this chapter like you used to in your prior in-person review sessions! Thanks so much
Thank you so much! I always struggled with this and got confused but now I understand it perfectly!
@ChadsPrep
11 ай бұрын
Glad to hear it - Happy Studying!
awesome Chad can not tell you how much you made my life easier thanks
@ChadsPrep
Жыл бұрын
You're welcome - Glad to hear it!
Studying for my DAT right now, I forgot how to do configurations and this is a life saver. Thank you so much!
@ChadsPrep
Жыл бұрын
Yoou're welcome - Happy Studying and hope you do well on your DAT.
i really needed this, thank youuuuuuuuuu
@ChadsPrep
Жыл бұрын
Glad the channel is helping you, B!
Thank you so much understood this concept after so much struggle!🙂🙏
@ChadsPrep
8 ай бұрын
You're very welcome.
Hi Chad! I have a question. So at 18:29, for the second example we are looking at, is it *necessary* to go label all of the C's and H's? Since we know the C on the right has a longer carbon chain, is it okay to just assume that that would be ranked above the one on the left?
You're the man!
@ChadsPrep
3 жыл бұрын
Woo Hoo! Thanks, Rohan!
Three years later and this helped me out ❤,thanks so much
@ChadsPrep
6 ай бұрын
You're very welcome - glad it did!
Thank you!! you explained this so well
@ChadsPrep
6 ай бұрын
You're welcome and Thank You.
Thanks dear sir Chad, your lecture helping me alot.i,m studying in Italian language but i can,t understand my professors lecture well due to language barrier. your lecture help me alot
@ChadsPrep
5 ай бұрын
Glad the channel is helping you!
EXCELLENT!!!! This is *extremely* helpful!! Just curious, is it normal for someone to cover all of chapter 5 in this series in a week (all of stereochemistry)? Or teach IUPAC nomenclature all in one lecture?
12:22 "Ooo" Me when I learn new things cause u da bomb at explaining!
@ChadsPrep
3 жыл бұрын
I see what you did there! I had to go back and look to see what you were referring to. Glad you found this lesson helpful!😉
Chad thank you so much :) THANK YOU THANK YOU THANK YOU!!!!
@ChadsPrep
Жыл бұрын
You're welcome - You're welcome - You're welcome!
Thank you very much for your explanation and good examples 👍
@ChadsPrep
3 ай бұрын
You are welcome and Thank You!
Thank you. You are indeed a great teacher.
@ChadsPrep
9 ай бұрын
You're welcome and Thank You.
Thanks 👍 sir continue with the good work 💗🙏 I appreciate your work
@ChadsPrep
Жыл бұрын
You're welcome and Thank You!
Hi, if you are working backwards and are given the name first with an R and S then asked to draw the skeletal structure. How do you know which elements around the chiral carbon get the wedge the line and the dash? For example, if it was a hydrogen a bromine a methyl and an ethyl, which of the four gets the wedge, dash or line. Many thanks for your time
I😊 could not understand this in class but i got the concept now! thank you !
@ChadsPrep
Жыл бұрын
You're welcome!
How do you know that the lowest priority is going away or towards you
How do you do that when H is on the Planar
I don't know which course you are teaching but it is extremely similar to my jee mains syllabus Great explanation btw
@ChadsPrep
4 ай бұрын
Glad to hear that! Happy studying! :)
Very powerful brother
@ChadsPrep
2 жыл бұрын
Thanks!
you are my favorite ochem teacher tHANK YOU
@ChadsPrep
Жыл бұрын
You're welcome and Thank You!
that latin lesson at 3:30 led me to an interesting rabbit hole of etymology
@ChadsPrep
4 ай бұрын
I hope you enjoyed it :)
You help us very much sir
@ChadsPrep
Ай бұрын
Glad to hear it
Hi Chad, At 10:48, how come there is only 1 chiral center? Would the Carbon under the O double bond not count as another carbon center?
@ChadsPrep
9 ай бұрын
Hi Rohit! The carbon under the oxygen is sp2 hybridized and trigonal planar. As such it is only bonded to 3 atoms. Only sp3 hybridized, tetrahedral atoms have a chance of being chiral centers. Hope this helps!
I got lots of wrong answers not understanding the effect of Hydrogen’s position with just reading my laboratory manual. I should have watched this video. This just made stereochemistry easier to understand.
@ChadsPrep
Жыл бұрын
Glad it helped - Happy Studying!
Could you please make a playlist on E/Z isomerism? I noticed you did not cover that topic and also compare it with cis/trans and R/s pls.
@ChadsPrep
7 ай бұрын
Hey Saimoon - check this video out: kzread.info/dash/bejne/eaecraOLeJy9fJc.html
I don't usually comment but, this video was very helpful thank you so much :)
@ChadsPrep
Жыл бұрын
Glad to hear it, Zohaa Sethi!
Chad, you are a lifesaver!! I do have one question: how do you know if an unseen H is on a dash or wedge? Thanks in advance!
@ChadsPrep
9 ай бұрын
In a bond line structure a tetrahedral atom is drawn having 2 bonds in the plane, 1 wedge, and 1 dash. So see which bond isn't drawn yet, and that is the type the unseen hydrogen atom must have. Hope this helps!
thank you so much, this really helped me a lot, I came here clueless.
@ChadsPrep
2 ай бұрын
Glad you found us!
Thank you so much sir
@ChadsPrep
9 ай бұрын
Most welcome.
You are amazing.. Thankyou so much Sir❤ Love from Pakistan❤
@ChadsPrep
11 ай бұрын
Thank you from USA - Happy Studying!
So, when you say 4 different groups- CH2 and CH3 are different, even though they are both carbon? (I would say they are different) If so, does this mean a chiral center cannot be double bonded?
@ChadsPrep
2 жыл бұрын
Hi again Vladimyr! Yes, 4 different groups need not mean four different atoms. A carbon bonded to methyl group, an ethyl group, a propyl group, and a butyl group would be a chiral center. And a chiral center must be tetrahedral (and therefore sp3 hybridized) so a carbon with a double bond could not be a chiral center. Hope this helps!
Thnuh so much sir ❤🎉😭😭😭😭
@ChadsPrep
10 ай бұрын
You are welcome - Happy Studying!
Hey Chad! Could you please tell me what that molecule in 10:55 to the left is called (in IUPAC)?
@ChadsPrep
2 жыл бұрын
Hey Youssef! The CH2SH group is a sulfanylmethyl so we have (S)-2-(sulfanylmethyl)butanoic acid
@MrYahya0101
2 жыл бұрын
@@ChadsPrep Thanks, I was wondering what that group was called.
@ChadsPrep
2 жыл бұрын
@@MrYahya0101 👍 👍 👍
🥺🫀please make more videos on this topic Special do some practice question this was really helpful 🎉❤
GOD BLESS YOU
@ChadsPrep
7 ай бұрын
Thank you - to you as well.
Shit man, thank you. You're so clear and concise
@ChadsPrep
2 жыл бұрын
You're welcome!
I totally left a like because I feel bad for bald guys lol. THANK YOU CHAD!
@ChadsPrep
3 жыл бұрын
HA! You are welcome, Elissa.
I hope you have a patreon channel or something where we can donate/....amazing job
oh man.. thats a whole process
@ChadsPrep
8 ай бұрын
Practice makes it easier I promise :)
At 16:15 why is it that you count SH as S H H instead of H H as it should be bonded. When you look at the substituent groups and what it's bonded to, you write what it's bonded to and not the group itself. Say for the first example you say O O O instead of C O O, not counting the carbon? My big question is why you are comparing S to O's when you should automatically declare S as first priority automatically as it should be compared to carbons, not the oxygen it's attached to.
@ChadsPrep
4 ай бұрын
I'm not sure I understand this question as there is no S at this point in the video. Do you mean carbon?
@ethanchen4504
4 ай бұрын
@@ChadsPrep It is when you're assigning R and S configurations. For the molecule on the very left, you are comparing S with O. However, S is directly connected to the chiral carbon while the O is connected to the carbon CONNECTED to the chiral carbon.
@ChadsPrep
4 ай бұрын
Ah got you - it is for the previous example around the 13:00 min mark correct? The chiral carbon is the one marked with a star, so the CH2(SH) is one group and COOH is another, both S and O are one carbon away from that starred chiral carbon if you go back and check
I’ll never learn ochem, I just fucking hate it with a passion. Like they go out of their way to make it complicated. In physics they just do clockwise negative counterclockwise positive. In ochem they have to look at it 5 different ways and pick the worst way to look at it and then categorize it that way
@ChadsPrep
Жыл бұрын
I totally get how confusing it can be, stick at it! You got this :)
@forlornhauntedghost
11 ай бұрын
Are you feeling better about Ochem now? I know it's been like 8 months since this post but I hope you were able to learn the material and understand it
pls don't jump my comment I really need help for my assignment. my question is if we got two chiral and they have the same designation that means both r or s how can we rename it? 2.if we are asked to put the relation after we assign r or s and if we ger 2R,3R and the same for the second one what is the answer us it diastereomers or enatiometric? pls give me answer I am your subscriber and follower
@ChadsPrep
7 ай бұрын
1. Whether both chiral centers have the some configuration or different configurations, you would still list the designation with the carbon number at the beginning of the name [ex. (2R, 3R)- or (2S, 3S)- or (2R, 3S) or (2S, 3R)]. 2. Also, if the two structures your are comparing have the same bond connectivity, then they are either identical or some form of stereoisomer. If their chiral centers are in the same configurations, then they are identical. If all their chiral centers are in the exact opposite configurations, then they are enantiomers. If some of their chiral centers are in the same configuration, and some are in the opposite configuration, then they are diastereomers. I go over this last part in the very next lesson in the playlist 😊