Okay I've been trying to figure this out forever. I'm horrible at imaging spatial arrangements of the groups and trying to rotate in my head so... if the 4th (lowest) priority group is facing OUT of the page. Just determine R vs S without doing anything and then the correct answer is the opposite answer. if the 4th priority group is on the PLANE of the page, you have to switch the 4th priority group with whatever group is facing INTO the page. It helps me to do a quick redraw of the molecule on paper. Then determine R vs. S. But since we initially had to change the absolute configuration/spatial arrangements of the molecule, the correct answer is the opposite answer. Hope this helps others! I've been stuck on this concept for hours lol
If we go by what's explained in this video, your second point is kinda wrong: If the lowest priority group (4th) is on the plane, you're not allowed to switch it with ANY group. Notice how in the last example, the *carbon chain* in the plane is the 4th group and isn't switched with the *chlorine* , the second priority group facing into the plane. So, I think the more detailed way to state the underlying rule here is that: _You're allowed to switch only the groups facing out of or into plane. If the lowest priority group (4th) is on the plane, you go for the second or third lowest priority group facing out of or into the plane and swap them._
@@samuraijosh1595 Good point! I got the second point based off of The Princeton Review - Organic Chemistry Review 3rd Edition. I'm more than happy to provide a screenshot of the page where I got it from. Not sure if it's available on Google books to look up, or if anyone has the book, it's on page 84. Example 4-13 d) "The lowest priority group is neither going in nor coming out of the plane of the page. One method is to rotate the molecule so the lowest priority group is in the back and redraw the molecule. Since the path is traveled clockwise, the configuration is R" * then the figure is them rotating the molecule, which for me is difficult to visualize in my head. they then continue on with the answer explanation: * "Here's a trick to help in the rotation of the molecules. Exchanging two groups on a chiral center necessarily changes the absolute configuration. So in this case, it is perhaps most convenient to exchange any two groups such that the lowest priority group is going into the page" * the figure then shows them exchanging H (lowest priority, which is on the plane of the page) with D (which is third priority and going into the page) * "Note that this trace is going counterclockwise. Remember, however, that we exchanged two groups (the hydrogen and deuterium (D)), which necessarily changes the absolute configuration. Since the counterclockwise trace in the altered molecule means an S configuration, the true configuration is R". That was a lot, but again I'm more than happy to screenshot for anyone who may need to see the actual figure to understand :)
@@JoannaGiron _"The figure then shows them exchanging H(lowest priority group on the plane) with D(third priority group going into the page)"_ Hmmm, that's interesting.... Then, I think I might've to look into this topic a bit more before moving on to other stuff, Ughh..... Anyways, thanks for taking the time to write all that out! :)
For the last example, and following your previous logic of changing the configuration to the opposite one without the need to actually rotate the molecule so the lowest priority face away from you before determining the R or S configuration. To follow your previous logic, looking at the compound, it is an S, but you need to change it to an R to account for the fact that the lowest priority (ethyl group) is not facing away from us. Why didn't we apply that rule here which seems more straightforward without the need to rotate anything in your head? Thanks for your great explanations
I believe you only reverse the conformation when it's a Hydrogen group facing towards you. Here there is no single Hydrogen group attached to the chiral center so the conformation follows the rule of obeying the clockwise or counter clockwise based on the original numbering
For the last one, the series is anticlockwise but considering the fact that Chlorine is facing away from us, aren't we supposed to to switch it from S to R? (without rotating the compound)
+Luna Rumba Tamang No, because the Carbon chains cant be "facing" us or away, so only Br and Cl can "face" in some way, and since Cl is the lowest priority between those 2, it's correct
I thought as much based on the logic of his previous video. Looking at it, it is S, but you change it to R to account for the fact that the lowest priority (ethyl group) is not facing away from us.
sorry, but that method of putting number 4 back, is not helpful at all ! we won't have the molecular models on our exam, and it's hard to IMAGINE them that way !
I'm sure you had your exam already but this is for if you still need it and anyone else. He mentioned it briefly, but you don't need to imagine anything at all if you don't want to. If the lowest number substituent (in these cases H) is on a wedge (toward you) then leave it. Assign all the numbers and figure out what direction it's going. If the direction is counterclockwise, it would be S. If it's clockwise, it would be R. Take that and reverse it. So if you get R, it's S. If you get S, it's R. This is because spinning the entire molecule on axis would flip flop the positions while putting the lowest number substituent in the back, so it the priority order would be reversed.
Thank you so much! I was having a hard time with the lowest priority group not pointing either in or out from the paper
Hey guys .... the last example ....should be R not S bcs the 4th atome aren't away frome us ..... we should make a switch .should not we ??
Okay I've been trying to figure this out forever. I'm horrible at imaging spatial arrangements of the groups and trying to rotate in my head so...
if the 4th (lowest) priority group is facing OUT of the page. Just determine R vs S without doing anything and then the correct answer is the opposite answer.
if the 4th priority group is on the PLANE of the page, you have to switch the 4th priority group with whatever group is facing INTO the page. It helps me to do a quick redraw of the molecule on paper. Then determine R vs. S. But since we initially had to change the absolute configuration/spatial arrangements of the molecule, the correct answer is the opposite answer.
Hope this helps others! I've been stuck on this concept for hours lol
If we go by what's explained in this video, your second point is kinda wrong: If the lowest priority group (4th) is on the plane, you're not allowed to switch it with ANY group.
Notice how in the last example, the *carbon chain* in the plane is the 4th group and isn't switched with the *chlorine* , the second priority group facing into the plane.
So, I think the more detailed way to state the underlying rule here is that:
_You're allowed to switch only the groups facing out of or into plane. If the lowest priority group (4th) is on the plane, you go for the second or third lowest priority group facing out of or into the plane and swap them._
All of what I said is based only on this video, so if you know better sources that say otherwise, feel free to correct me......
@@samuraijosh1595 Good point! I got the second point based off of The Princeton Review - Organic Chemistry Review 3rd Edition. I'm more than happy to provide a screenshot of the page where I got it from. Not sure if it's available on Google books to look up, or if anyone has the book, it's on page 84. Example 4-13 d)
"The lowest priority group is neither going in nor coming out of the plane of the page. One method is to rotate the molecule so the lowest priority group is in the back and redraw the molecule. Since the path is traveled clockwise, the configuration is R"
* then the figure is them rotating the molecule, which for me is difficult to visualize in my head. they then continue on with the answer explanation: *
"Here's a trick to help in the rotation of the molecules. Exchanging two groups on a chiral center necessarily changes the absolute configuration. So in this case, it is perhaps most convenient to exchange any two groups such that the lowest priority group is going into the page"
* the figure then shows them exchanging H (lowest priority, which is on the plane of the page) with D (which is third priority and going into the page) *
"Note that this trace is going counterclockwise. Remember, however, that we exchanged two groups (the hydrogen and deuterium (D)), which necessarily changes the absolute configuration. Since the counterclockwise trace in the altered molecule means an S configuration, the true configuration is R".
That was a lot, but again I'm more than happy to screenshot for anyone who may need to see the actual figure to understand :)
@@JoannaGiron _"The figure then shows them exchanging H(lowest priority group on the plane) with D(third priority group going into the page)"_
Hmmm, that's interesting.... Then, I think I might've to look into this topic a bit more before moving on to other stuff, Ughh..... Anyways, thanks for taking the time to write all that out! :)
@@samuraijosh1595 Not a problem :)
For the last example, and following your previous logic of changing the configuration to the opposite one without the need to actually rotate the molecule so the lowest priority face away from you before determining the R or S configuration. To follow your previous logic, looking at the compound, it is an S, but you need to change it to an R to account for the fact that the lowest priority (ethyl group) is not facing away from us. Why didn't we apply that rule here which seems more straightforward without the need to rotate anything in your head? Thanks for your great explanations
i think Nothing is hard if the explanation is simple. Thanks a lot i Was having hard time
Isn't the last one R? Since it's facing ''4'' isn't facing away?
I believe you only reverse the conformation when it's a Hydrogen group facing towards you. Here there is no single Hydrogen group attached to the chiral center so the conformation follows the rule of obeying the clockwise or counter clockwise based on the original numbering
@@ginar3398 The rule says the lowest priority has to face away from you. Hydrogen is not always the lowest priority in an chiral center
this vid helped me better understand it than my teacher in my senior year of HS could and my firstyear uni professor could
It's pure gold. Thank you so much!
For the last one, the series is anticlockwise but considering the fact that Chlorine is facing away from us, aren't we supposed to to switch it from S to R? (without rotating the compound)
+Luna Rumba Tamang i thought the same thing too :/
+Luna Rumba Tamang No, because the Carbon chains cant be "facing" us or away, so only Br and Cl can "face" in some way, and since Cl is the lowest priority between those 2, it's correct
I thought as much based on the logic of his previous video. Looking at it, it is S, but you change it to R to account for the fact that the lowest priority (ethyl group) is not facing away from us.
wow. what a wonderful explanation!
thanks a lot, Khan Academy. I will surely pass my organic chemistry test today, rs
Thanks a lot sir.
Could you have made the other side the double bond and vice versa? I guess what I'm asking is how to tell which side the double carbon bond starts at
Simply Awesome!
Merci bcp Monsieur 👏
Thanks for doubt clearing problems 😉😁
Thanks a lot for this helpful exercise!
Omg man, thank you so much.
great,thank you
I wish you could be me my Professor......................
Yeah, I wish the same..
You are great :-)
in the first one how is the carbon you marked is a chiral centre? two grps are same on that CH2
But the next two group is different from left and right side that is from left side is CH2 but from right side that is CH
8:24 incorrect
sorry, but that method of putting number 4 back, is not helpful at all ! we won't have the molecular models on our exam, and it's hard to IMAGINE them that way !
I'm sure you had your exam already but this is for if you still need it and anyone else. He mentioned it briefly, but you don't need to imagine anything at all if you don't want to. If the lowest number substituent (in these cases H) is on a wedge (toward you) then leave it. Assign all the numbers and figure out what direction it's going. If the direction is counterclockwise, it would be S. If it's clockwise, it would be R. Take that and reverse it. So if you get R, it's S. If you get S, it's R. This is because spinning the entire molecule on axis would flip flop the positions while putting the lowest number substituent in the back, so it the priority order would be reversed.
@@jewbybrother579 but what if the hydrogen is in the plane of the page.. I cant visualise roating it, is there a rule for that??
Videos would be better if you named these.
The last one 😣😣😣😣😣😣😣