A tip that one of my lecturers told me is if the hydrogen is coming out of the page merely find out if the molecule is R or S at that point and then do the opposite of whatever you got.

@BS2all

9 жыл бұрын

supaahflyy Can someone confirm if this always works?

@kingof011

9 жыл бұрын

BS2all it does because when you have hydrogen attached, it will always be your lowest priority and your lowest priority is supposed to be going away from the page.. (biochemical engineering student at UGA)

@UneasyTortoise

8 жыл бұрын

can confirm

@matin7983

7 жыл бұрын

I thought it was if #4 was on the wedge

@gamefreak2050

7 жыл бұрын

But if we use that method here, wouldn't we get S anyways (in the beginning, going from methyl group to fluorine to bromine is counter clockwise while the hydrogen is a wedge), so since the hydrogen is a wedge and we do the opposite like you said then we should say that it is an R configuration but Sal says it's S at the end? Am I looking at this the wrong way?

All you'd really have to do is switch the priority 4 atom with the atom going into the page (dashed), then switch the other two molecules, then you're done and can find R or S. Give it a try. My source is David Klein - Organic Chemistry - Second Edition - Pg.205. No reason to make things more complicated than they really are.

I am DEFINITELY going to recommend these videos to my classmates. Thank you so much for posting these! Chirality and stereoisomers are really challenging for me.

Because of your teaching, I enjoy and love chemistry now.

You are amazing, seriously I would not have survived my OChem class without you. THANK YOU SO MUCH

I am also doing my first year of med school in Luxembourg, and you are a total lifesaver. English tutorials are THE BEST!

Cool! I love the umbrella analogy! 😊🎉

Epic teaching. You were born to teach. Absolutely the best presentation I ever seen on Chemistry. THANK YOU. Wow.

Understood the concept completely, Thank you so much Sal :)

I .. I just want to cry!!! You're AMAZING! :')

Wow!! You are an amazing teacher! I will no longer feel bad about skipping O-chem class! You could totally be a professor (maybe you already are?). Thank you SO much, you are an amazing person for doing this for everyone :)

this example molecule was amazing, really helped explain a bunch of rules.

un genio total, excelente explicación

God Bless You for this awesome videos .. i'm also student in my first year in medicine and always can't understand any word from the lecture but ur videos make me do .. THANK YOU

Thanks a lot for your videos ! I'm on the first year of medicine and your explanations are much better than my teacher's

Thank you wvery much for your work. It makes understanding much easier

you sir are a gentleman and a scholar. Thanks for saving my butt on multiple occassions.

the best explanation ever.

some really good stuff here

Thanks sal! U r GR8!

Thanks for the lesson Khan :)

This is so awesome.

I completely understand this but cannot figure it out when on a cyclohexane

F-in' LOVE khanacademy!!! saved me tons on tutors!!!

U r very helpful even i don't speak english very well i could understand u well thanx =)

very helpful thank u so much

Thanks a lot!

Thank you.

May God bless you ✋

Thank you so much for this, I love you! (no bromo)

That's why they're good at double speed! Thank goodness for the HTML5 trial.

Thanks a lot! I am a medical student and unfortunately our chemistry student really couldn't explain this well enough for me to understand it.

how does he know everything?!?

@nangku2034

6 жыл бұрын

shine1213 bcz he is the god of chemistry

yeah that was my question

@markgia for a double or triple bond: say you have a double bond, you will treat it as two single bonds connected to whatever that double bond is connected to. and for a triple bond, it's the same thing, just treat that as three single bonds connected to whatever that triple bond is connected to. hope this helps

You just saved my O Chem grade.

That third methyl on the third carbon of the chain is actually a part of the chain. That's why it's butane rather than propane: a chain of four carbons. Attached to that chain are only two methyl groups, on positions 2 and 3.

why can't you think of #2 as the "handle of the umbrella" and rotate 1,3,4 clockwise?

Papa Khan you're my hero

Sorry sir,may I know why when we do rotations for the molecules as to put hydrogen at the back,the number 1 group stays where is it?

Does the ''handle of the umbrella'' always has to be the number one group? And if not How do I know which one is?

good video, it just have 1 question with a unique case. how do i rank the Group in serine. i tried to rank the alcohol Group and Carboxylic acid Group. PLS HELP!!!

6:00 why didn't you compare fluorine with the H_2 atoms instead of bromine

does anyone know why he didnt put the methyl group on the very end of the carbon chain in with the naming? he did 2,3 di methyl..but what about the first methane that was all the way to the left....but besides that..your videos are AMAZING!

Like he says in the video, picture the number 1 carbon as being the handle to an umbrella, and the bond being the rod. Remember, since there aren't any Pi bonds, this molecule has free rotation about ANY of the Carbon bonds. He could have rotated about any one of them. So you could view any of (1,2,3 or 4 ) as the "handle of the umbrella" He simply picked that one because its easiest to rotate about that bond to get the lowest priority Hydrogen in the back.

Just wondering why towards the end, he placed the 2 where the 4 used to be? Could I just have swapped the 4 and the 3 so that it would be clockwise and then since i used the swap rule, make the molecule S instead of R?

Hey can anyone please explain to me why a OH group is of higher priority than a COOH?

ahh can you tell ways you got into medical school?! or just about the process. i'm a sophomore in college so I'm getting nervous!

Se fosse com legenda eu ficaria tão feliz :DD

CH3CCCH2 is the chain, its part of the carbon chain

why is the CH2-br group considered as a simpler group than ch3?

NICE

Why didn't you rotate #1? How do you knw if you are going to rotate a certain one or not?

Why you rotate it this way?

Do you not have to indicate the position of the R/S configuration? Meaning that the molecule name would be: (2S)-1-Bromo-3-Fluoro-2,3-dimethylbutane?

@TheExCKnight

8 жыл бұрын

Not in this case, no, as there is only one chiral carbon, so it does not need to be specified which carbon that is. :)

@luisaceo00 When comparing 2 different groups, you compare each element of the groups one at a time. The first element of the OH group is O which has an atomic mass of 16 . The first element of the COOH group is C which has 12g/mol for it's atomic mass. Thus, the very first point at which the two groups differ, Oxygen is heavier than C. So, OH > COOH.

can anyone explain to me how do I see how to rotate the molecule? because I see it like oh i can just rotate the molecule in a spin and the 4th group will switch places with the 3rd group and thats it... I dont get why he moved 4-->2-->4

4:17 is where lecture begins

Instead of rotating, just flip from R to S. If the hydrogen is coming out of the screen (i.e, #4).

could we put (2S) infront of the name ? y is putting just S sufficient ?

i love you...

just put R raised to the I which means the inverse which would make it S

If a stereocentre is bonded to an alcohol and carboxyl group, the oxygen has a higher atomic mass than the carbon, giving it higher priority.

live.savor.

DEAR SIR,IN THE FIRST EXAMPLE AT NO-3 OF THIS MOLECULE-2METHYL GROUPS ARE ATTACHED (NOT ONE),SO WILL CAUSE A NAME CHANGE TO 2,3,3 TRIMETHYL

I smell Group Theory!

No time to waste, got to cover 3 chapters. Going to the bathroom with khan academy on the cell phone.......

If #4 is: Dashed: CW = R, CCW = S Wedged: CW = S, CCW = R Plane(straight line): Swap #4 with dashed, determine current R/S with CW/CCW, answer is opposite of current configuration This should be it. Correct me if I'm wrong.

why is it not 1-bromo-3-fluoro-2,3,3-trimethylbutane? I thought those are to methyl groups on the 3rd carbon.

@03raq

5 жыл бұрын

1-bromo-3-fluoro-2,3,4 trimethylbutane I also have the same doubt except i thought the last methyl is attached to #4

#22

If the last priority atom is not in the back . The easiest way is to just leave it as it is and consider the opposite configuration. meaning if it is S with H (or any last priority atom) on a wedge it woud be an R and vise versa

@rajatbhat7799

8 жыл бұрын

+Ayah gawad Does it work every time in any type of question(like cyclic/aromatic etc.) Please reply back. Its important.

@ayahabdelgawad2850

8 жыл бұрын

If the last priority atom is on a Wedge (thats most of the time a hydrogen atom) then it works but if its like on the plane of the page it won't work all the time

@rajatbhat7799

8 жыл бұрын

+Ayah gawad yes, the "not working" case is the doubt for me. for eg- the highest priority group is inside(dash) the page and hydrogen is on plane of page, does it work? The second question in the given link is my doubt - chemwiki.ucdavis.edu/@api/deki/files/1538/newest_problems.JPG?size=bestfit&width=392&height=315&revision=1

@ayahabdelgawad2850

8 жыл бұрын

no in that case u can't do that.. you would have to alter the configuration in a way that will make highest priority on wedge.. if you can't visualize it you should use a model kit

@rajatbhat7799

8 жыл бұрын

+Ayah gawad But, if I make the highest priority molecule bromine in wedge(towards me), Hydrogen being in a 90 degree position w.r.t. Br, will never go inside the page. How do I do that? And what will it be - R or S?Can you clear this doubt to me?Sorry for bothering you, and thanks for the previous comments.

That would be too complex....even for the khan academy.

you need to post some videos on how to get girls

which guy is he talking about????

[ =D ]do anyone else see that