Orgo Chem question

[151AND8TH]

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When naming using (R and S) designation for 1-Bromo-2Fluorocyclohexane, I am having trouble seeing how it is named (1S,2R)-1-Bromo-2Fluorocyclohexane instead of (1R,2S)1-Bromo-2-Fluorocyclohexane. I thought on the 1 carbon, Br would be (a), the 2 Carbon-Fluoride would be (b), the 6 carbon would be (c) and H would be (d).. my question is once you draw this out it looks as if the molecule should be named (1R,2S)1-Bromo-2-Fluorocyclohexane. would anyone care to explain ? Thank you

 

[Chga]

i am getting the same answer as you... where did you get this question from?

 

[joonkimdds]

I am also getting the same answer as you.
And here is my question.
Does this question come up with a picture?
If carbon #1 has H that has wedge line instead of dotted line, then we should make it go away from you(into the paper) thus R becomes S.
But if there was no information given about the orientation of the structure, then I don't know.

p.s. I like ur quote 🙂
btw, I want to be a part time dentist. I think that's also something no one ever tried before.

 

[Flipper405]

Your prioritizing is correct, but I'm drawing it as (1S,2R) with no problems. When I draw it, bromine and flourine are "cis", so that if you are looking at it from their side, they are both pointing out of the page with flourine on the left and bromine on the right OR if you look from the other side, they are both pointing into the page with bromine on the left and flourine on the right.

Good luck.

*edit* You could also draw (1R,2S) but that is a different compound. It all depends on your stereochemistry.

 

[Imperium]

They can be either. There's not enough information to tell you specifically what they are.

 

[drdeeeena]

if you want to name the cpd according to S, R, you need first to assign the the group with the highest priority as a Wedge, followed by the 2nd and third while the H should be assigned as a dash line (since you have to push the H behind the C atom of ur interst!) then you assign priorities where Br (a), C with the F (b) then C with the other part of the cyclo then the H... you should get an S conformation.

Please refer to the attached pic

P.S having an orgo model kit helps alot with the visualization of S+ R

 

[151AND8TH]

Your prioritizing is correct, but I'm drawing it as (1S,2R) with no problems. When I draw it, bromine and flourine are "cis", so that if you are looking at it from their side, they are both pointing out of the page with flourine on the left and bromine on the right OR if you look from the other side, they are both pointing into the page with bromine on the left and flourine on the right.

Good luck.

*edit* You could also draw (1R,2S) but that is a different compound. It all depends on your stereochemistry.

you are correct.. after I had something to eat, it all appreared very clear 🙂 (never study on an empty stomach)

below is a picture of the molecule..

http://www.emolecules.com/cgi-bin/more?vid=12826822

 

[151AND8TH]

I am also getting the same answer as you.
And here is my question.
Does this question come up with a picture?
If carbon #1 has H that has wedge line instead of dotted line, then we should make it go away from you(into the paper) thus R becomes S.
But if there was no information given about the orientation of the structure, then I don't know.

p.s. I like ur quote 🙂
btw, I want to be a part time dentist. I think that's also something no one ever tried before.

🙂 part time Dentist part time business man ..or perhaps part time movie star!! 😕.... not a bad idea..

 

[joonkimdds]

Flipper said Br and F should be Cis, but the picture you provided shows that they are trans so who is right? and how do we know if they are cis or trans and why does it matter? I thought all it matters is whether H is coming towards you or away from you.
So I think answer can be both like Imperium said there isn't enough info given in my opinion.

 

[Flipper405]

Flipper said Br and F should be Cis, but the picture you provided shows that they are trans so who is right? and how do we know if they are cis or trans and why does it matter? I thought all it matters is whether H is coming towards you or away from you.
So I think answer can be both like Imperium said there isn't enough info given in my opinion.

The molecule drdeeeena drew has them pretty much the way I described (although the F is on a straight line which makes things ambiguous for carbon 2, but doesn't matter for carbon 1 designation). The one 151AND8TH provided is actually (1R,2R).

I don't ever really see what the "question" was to be honest. The R and S designations will depend ENTIRELY on how you draw all the substituents. You can know if they are cis and trans in this way: if they are both on wedges or dashed lines, they are cis; otherwise, they are trans... if you don't know this, you have to go review your ochem textbook because this is very basic stuff. It matters because that's a very common way stereochemistry is shown. The H coming towards you or away from you is one part of the picture, but you can't rely solely on it to determine the stereochemistry.

 

[joonkimdds]

The molecule drdeeeena drew has them pretty much the way I described (although the F is on a straight line which makes things ambiguous for carbon 2, but doesn't matter for carbon 1 designation). The one 151AND8TH provided is actually (1R,2R).

I don't ever really see what the "question" was to be honest. The R and S designations will depend ENTIRELY on how you draw all the substituents. You can know if they are cis and trans in this way: if they are both on wedges or dashed lines, they are cis; otherwise, they are trans... if you don't know this, you have to go review your ochem textbook because this is very basic stuff. It matters because that's a very common way stereochemistry is shown. The H coming towards you or away from you is one part of the picture, but you can't rely solely on it to determine the stereochemistry.

I know that both on wedge or dash means cis; otherwise they are trans.
But I don't know if 1-Bromo-2Fluorocyclohexane has Br and F cis or trans when it didn't provide picture or it didn't say cis or trans in front of the name.
so I thought that this question has two answers since we don't know if they are cis or trans yet. Depending on whether they are cis or trans, they should have different designation, thus different answers(I think...).

 

[dontwakeme]

Question is completely ambiguous. Both stereocenters could be R and S i.e. RR,SS,RS,SR. You cannot provide a name for it without a 3-d picture.

 

[dontwakeme]

I know that both on wedge or dash means cis; otherwise they are trans.
But I don't know if 1-Bromo-2Fluorocyclohexane has Br and F cis or trans when it didn't provide picture or it didn't say cis or trans in front of the name.
so I thought that this question has two answers since we don't know if they are cis or trans yet. Depending on whether they are cis or trans, they should have different designation, thus different answers(I think...).

Just for clarification, cis/trans designation should only be used when you have oppositely substituted rings (no chiral centers). In ortho substituted cases (such as this one), generally, you don't use cis/trans because you have chiral centers.

 

[joonkimdds]

Question is completely ambiguous. Both stereocenters could be R and S i.e. RR,SS,RS,SR. You cannot provide a name for it without a 3-d picture.

That's how I think, too. and I got an A in OCHEM1, LOL... 😛

 

[Flipper405]

Just for clarification, cis/trans designation should only be used when you have oppositely substituted rings (no chiral centers). In ortho substituted cases (such as this one), generally, you don't use cis/trans because you have chiral centers.

This is not ortho. Ortho, meta, and para are only for benzene derivatives, but yeah, cis/trans shouldn't really be used here either... I tried to indicate with the " marks that I was just using that for abbreviation.

 

[dontwakeme]

This is not ortho. Ortho, meta, and para are only for benzene derivatives, but yeah, cis/trans shouldn't really be used here either... I tried to indicate with the " marks that I was just using that for abbreviation.

I know that. I used ortho for lack of a better word. You get the idea though. It still makes perfect sense if you know anything about organic chemistry.