Great video! I have been prowling the web for a better understanding and the fact that you didn't talk about the bond rotation truly helped me. THANK YOU!
this is the BEST video for understanding these concepts, you're best work by far! i love it bc the bulk of it is based on examples, and its step by step. giving problems for me to do (and get wrong twice >.< but hey after watching them all I've got it down) makes it a model for how i wish organic chemistry tutorials were
You have the best organic chem videos!!! It's much more helpful than my professor lectures or reading the text book. Thank you so much!! Keep doing your great work :)
I really don't understand the concept of R/S. At 4:46, you see the configuration goes clockwise which means it is R, due to the atom number. And then you say #4 atom which is H, is in front and therefore it suddenly is S??? It is still R when looking at the atomnumbers? I am so confused lost right now...
The rules say that when the #4 substituent is in the back (dash) , if 1,2 and 3 trace a clockwise path, the stereocenter is R. If 1,2 and 3 trace a counterclockwise path, the stereocenter is S. In our case, the #4 substituent is in the front (wedge). We *could* rotate the molecule so that the normal rules apply, but this is a pain to do on paper and it's easy to make a mistake. Therefore, what I did here was to use the "reverse rules". Since #4 is in the front (wedge) since 1,2 and 3 trace a clockwise path, we use the "reverse" of the rule, and therefore the stereocenter is S. It's a bit like looking in a rear-view mirror. Imagine looking at your friend in a rear-view mirror holding up his right hand, and he asks you what hand he is holding up. Since you know that you are looking in a mirror and the mirror reverses everything, you use the *reverse rules* so you say, "Left!".
If you look at your left hand in a mirror, it looks like it's your right hand. If you *know* you're looking in a mirror, you can correct for this by using "opposite" rules (right is left, left is right) and therefore you get the correct answer! Same principle! :-)
What if #4 is in the plane of the screen/paper (solid line)? Is the correct answer R/S still the opposite of what's expected (clockwise/counterclockwise)?
How are they enantiomers? They are not mirror images. I see the connections and the R/S but how does that correlate to being enantiomers when enantiomers have to be mirror images? Non superimposable mirror images I believe correct me on that.
Can anyone explain? I did my usual way of putting H in the back for the first molecule, but it still goes clockwise for me. I'm not seeing how it would go counter clock wise!
The way the first molecule is drawn, 1, 2 and 3 priorities *do* go clockwise. However, R/S is always determined with #4 being in the back. Since #4 is in the *front* here, we use "opposite rules". So 1, 2, and 3 going clockwise actually results in an S stereocenter when #4 is in the front. If you make a little model and rotate it around so that you put #4 in the back, you'll see that 1,2 and 3 "magically" now go counter-clockwise. So this little "opposite" trick saves you the time of making models, etc.
Sir I have confusion with the 1st compound for me it seems to be R configuration as it is clockwise but you said it's S. Please help me to get rid of this query
Arent they constitutional isomers... however they are better labeled as enantiomers . Doesn't mean they are not constitutional isomers. They are constitutional isomers, not confirmation isomers ( because there is no rotation about a sigma bond) , but are stereoisomers, more specifically enantiomers.
If the H atom is in the plane, here's one tactic that you can do, which employs the "single swap rule". Swapping *any two groups* with each other on a stereocenter, will flip that stereocenter from R to S (or vice versa). Just like looking in a mirror *swaps* the appearance of your left and right hands (your left appears to be right, and your right appears to be left). Knowing this, *swap* the H in the plane with whatever group is in the back (wedge). Redraw. *Then* determine R and S. Once you've determined R and S, you then need to correct for the fact that you did a single swap (just like when looking at your hand in a mirror, you need to correct for the fact that you're looking in a mirror to be able to determine the "correct" hand - it will be the opposite). So the correct R/S value will be whatever is the opposite of the R/S you determined in the swapped version.
R and S is determined with the #4 group being in the back. In the first example, #4 is in the front. Therefore we can get the same answer if we apply "opposite" rules. Since 1, 2 and 3 proceed in a clockwise direction when #4 is in the front (wedge), they must proceed in a *counter clockwise* direction when #4 is in the back (dash). Therefore we get S.
It is true that if the H is on the side, one cannot use the "opposite" rule. However one can still use the "single swap" rule. Redraw the molecule with the H in the back and the "back" group on the side, and determine R/S as normal. Then flip the result.
Glad it helped! I would like to invite you to check out our monthly (no long term commitment) membership with over 1500 quizzes, flashcards the reaction guide and more. Here's access: bit.ly/2YctxPb
Guys don't listen to his "rule" about switching, I have tried the rule and it does not work, I then showed it to my professors and they said it has no consistency, this guy is a fake 100%
I read the section in my book twice, came to this video...understood it in minutes. Thank you!
Awesome! thanks for letting me know!
Finally! I get it! Nobody told me to check the R and S to see if they're. I have been staring at them for 20 mins trying to see how.. Thank you!
check the R and S yes, glad it helped
Great video! I have been prowling the web for a better understanding and the fact that you didn't talk about the bond rotation truly helped me. THANK YOU!
Yes! Thanks - everyone talks about bond rotations but it gets complex once a molecule gets big enough - glad you found this alternate method useful!
this is the BEST video for understanding these concepts, you're best work by far! i love it bc the bulk of it is based on examples, and its step by step. giving problems for me to do (and get wrong twice >.< but hey after watching them all I've got it down) makes it a model for how i wish organic chemistry tutorials were
thank you very much thomas underhill !
agreed!!!
You have the best organic chem videos!!! It's much more helpful than my professor lectures or reading the text book. Thank you so much!! Keep doing your great work :)
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Been struggling a bit trying to get a solid grip on stereochemistry -- & this seriously helped immensely!
Glad to hear it. Thanks!
honestly i never comment but your videos are sooooooooooooooo helpful that i can not just stay without complimenting your videos
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thank you so much! I've been stuck on this question since I took my stereochemistry test, and you really helped me comprehend what I was missing!
you have literally saved me from a mental breakdown. god bless you sir
Lol good luck
You are so welcome with the help on enantiomers
Saving me for my DAT 8 years later, thank you
Great to hear!
Thanks for your clear explanation and neat writing, very much appreciated!
I really don't understand the concept of R/S.
At 4:46, you see the configuration goes clockwise which means it is R, due to the atom number. And then you say #4 atom which is H, is in front and therefore it suddenly is S??? It is still R when looking at the atomnumbers?
I am so confused lost right now...
The rules say that when the #4 substituent is in the back (dash) , if 1,2 and 3 trace a clockwise path, the stereocenter is R. If 1,2 and 3 trace a counterclockwise path, the stereocenter is S.
In our case, the #4 substituent is in the front (wedge). We *could* rotate the molecule so that the normal rules apply, but this is a pain to do on paper and it's easy to make a mistake.
Therefore, what I did here was to use the "reverse rules". Since #4 is in the front (wedge) since 1,2 and 3 trace a clockwise path, we use the "reverse" of the rule, and therefore the stereocenter is S.
It's a bit like looking in a rear-view mirror. Imagine looking at your friend in a rear-view mirror holding up his right hand, and he asks you what hand he is holding up. Since you know that you are looking in a mirror and the mirror reverses everything, you use the *reverse rules* so you say, "Left!".
Brilliant .... very well explained. Thanks a lot.
If number 4 is in the front its opposite - why was i never told this?!
If you look at your left hand in a mirror, it looks like it's your right hand. If you *know* you're looking in a mirror, you can correct for this by using "opposite" rules (right is left, left is right) and therefore you get the correct answer! Same principle! :-)
This video really helped me understand this concept. Thank you!
Please check If we rotate 3 bonds fixing one in the 2nd molecule, we will get the identical molecules sir. These are identical right?
What if #4 is in the plane of the screen/paper (solid line)? Is the correct answer R/S still the opposite of what's expected (clockwise/counterclockwise)?
Your Vedio is just amazing....loves from IND
At 5:36 for the molecule on the right, why don't you rotate counterclockwise in the direction of the 3rd priority atom first?
Thank you so much sir for your clear explanation !!!🤗🤗
You are most welcome
Thank you for making R/S plain and simple to understand!!! Quiz this Friday;--)
Glad you found the R and S understandable~
Thanks for helping me to do the questions on enantiomers sir😀😀😀
It's my pleasure to help you with your questions on enantiomers
Thank you for posting this! it really is so helpful !
You are welcome
what do you mean by connectivity ? same atoms ?
amazing clarity
How are they enantiomers? They are not mirror images. I see the connections and the R/S but how does that correlate to being enantiomers when enantiomers have to be mirror images? Non superimposable mirror images I believe correct me on that.
Thanks sir u've cured my sickness
Can anyone explain? I did my usual way of putting H in the back for the first molecule, but it still goes clockwise for me. I'm not seeing how it would go counter clock wise!
Me2🤔
The way the first molecule is drawn, 1, 2 and 3 priorities *do* go clockwise. However, R/S is always determined with #4 being in the back. Since #4 is in the *front* here, we use "opposite rules". So 1, 2, and 3 going clockwise actually results in an S stereocenter when #4 is in the front.
If you make a little model and rotate it around so that you put #4 in the back, you'll see that 1,2 and 3 "magically" now go counter-clockwise. So this little "opposite" trick saves you the time of making models, etc.
Amazing! Thank you!
Thank you too!
oh ! this is realy awesome , thank you MR i understand now and then you save my mark for stereochemistry ^_^ thank you very much
Explained it better in 7 minutes than my org chem professor ever did at my 40K, a year, university
Awesome. Thank you!
thanks a lot, dude! helpful
I am not sure where the other video you were talking is located
Which topics were you interested in, I can hel send links
this is really good
Thank you
Welcome!
Couldn't understand what is R and S.
Sir I have confusion with the 1st compound for me it seems to be R configuration as it is clockwise but you said it's S. Please help me to get rid of this query
Hi , when H is in the front , you need to reverse the configuration, it was R clockwise but the H is in the front so reverse it to become S.😊
@@roseblanche9073 I got it, thanks
Thank you sooo much
Arent they constitutional isomers... however they are better labeled as enantiomers . Doesn't mean they are not constitutional isomers. They are constitutional isomers, not confirmation isomers ( because there is no rotation about a sigma bond) , but are stereoisomers, more specifically enantiomers.
Enantiomers are mirror images. Two molecules can't be mirror images if they're constitutional isomers.
Great video
thank you
How should I should I rotate the molecule if the hydrogen is in the plane of the paper?
If the H atom is in the plane, here's one tactic that you can do, which employs the "single swap rule".
Swapping *any two groups* with each other on a stereocenter, will flip that stereocenter from R to S (or vice versa). Just like looking in a mirror *swaps* the appearance of your left and right hands (your left appears to be right, and your right appears to be left).
Knowing this, *swap* the H in the plane with whatever group is in the back (wedge). Redraw. *Then* determine R and S.
Once you've determined R and S, you then need to correct for the fact that you did a single swap (just like when looking at your hand in a mirror, you need to correct for the fact that you're looking in a mirror to be able to determine the "correct" hand - it will be the opposite).
So the correct R/S value will be whatever is the opposite of the R/S you determined in the swapped version.
Awsome video...Thanks
thank you glad you found this helpful
i dont understand the first explanation.. its counterclockwise coz 4 is in the front? wut?
R and S is determined with the #4 group being in the back. In the first example, #4 is in the front. Therefore we can get the same answer if we apply "opposite" rules. Since 1, 2 and 3 proceed in a clockwise direction when #4 is in the front (wedge), they must proceed in a *counter clockwise* direction when #4 is in the back (dash). Therefore we get S.
But they arent mirror images
thanx a ton... exceptinal explanation... please do help us more
Thank you for the response, I will be adding more videos and explanations
such a good video, thanks :)
What if it's above or to the side??????? Only a video for specific problems are terrible
It is true that if the H is on the side, one cannot use the "opposite" rule. However one can still use the "single swap" rule. Redraw the molecule with the H in the back and the "back" group on the side, and determine R/S as normal. Then flip the result.
so sad that i found these videos after failing on my orgo exam
thank you so much! Spread the word if you know of others who could find our organic chemistry videos useful!
Oh I love you
Glad it helped! I would like to invite you to check out our monthly (no long term commitment) membership with over 1500 quizzes, flashcards the reaction guide and more. Here's access: bit.ly/2YctxPb
awsome
So glad the R and S video was helpful to you
Continue
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@@MasterOrganicChem I don't want paid plans
ssuuuper
Guys don't listen to his "rule" about switching, I have tried the rule and it does not work, I then showed it to my professors and they said it has no consistency, this guy is a fake 100%
To be more specific if the "front" H was pointing the other way it would not follow this rule, even if it is pointing to the front
If you flip any two groups on a chiral center it will flip R to S or vice versa. Try it.