Fischer projections. please help-kaplan final #71

[Dentalicous1234]

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I tried looking up old posts and using the Bruice textbook (if you know good pages in it please share!) but I can't figure it out. I got it right but can't understand it now.😱

PLEASE help. I don't know if we would be expected to do this on the real thing, I think so esp. cuz I remember some destroyer questions about being able to go from one projection to the other.

Can anyone simplify how they go the answer D in #77 and to best get to a fischer projection?😕😕

THANK YOU SO MUCH in advance 🙂

 

[Decan]

I dont have the kaplan test, but if you put the question up I may be able to help...

 

[Dentalicous1234]

I tried drawing it on word but can't get it on here so I'll my best to make it here:

BR
l
OH-- l----D
l
l
H--- l----OH
l
l
F

that has to be put in the other projection and the horizontal lines are coming out at you (dark solid) and the Br and F are on dashed lines going back behind the plane of the paper.

hopefully you can make out what' i'm trying to say and help cuz this is should be basic I don't know whY I can't see it in this problme 😕😕😕😕😕

 

[Dentalicous1234]

okay grrr it's not displaying right...basically the Br and F are on the vertical line and the others are on the horizontal like with
OH-----D
then
H-----OH

 

[Mstoothlady2012]

okay grrr it's not displaying right...basically the Br and F are on the vertical line and the others are on the horizontal like with
OH-----D
then
H-----OH

i still dont und wht it says... explain the molecule instead of drawing ..like 2 carbons 1 top which mis attached to this .... 2nd carbon which is attached to this...etc

 

[Dentalicous1234]

okay sorry i keep being so confusing, hopefully this is better 🙂


okay there are 2 carbons...
-the carbon on top is attached to Br, D, and OH (Br is on vertical line and the D is on the horizontal on the right, OH is on horizontal on left) and the second carbon.
-for second carbon (bottom half) it's attached to the first carbon, F (on vertical), OH (on right side of horizontal line) and H (on left side of horizontal)

hope this is clearer or if not can someone please just do a run down of how to do it when all the substituents are different for each carbon? I saw the science aid example but they just used CH3s and Hs and it didn't match up to the kaplan answers so I got sooo much more lost.

Thank you in advance 🙂

 

[Mstoothlady2012]

okay sorry i keep being so confusing, hopefully this is better 🙂


okay there are 2 carbons...
-the carbon on top is attached to Br, D, and OH (Br is on vertical line and the D is on the horizontal on the right, OH is on horizontal on left) and the second carbon.
-for second carbon (bottom half) it's attached to the first carbon, F (on vertical), OH (on right side of horizontal line) and H (on left side of horizontal)

hope this is clearer or if not can someone please just do a run down of how to do it when all the substituents are different for each carbon? I saw the science aid example but they just used CH3s and Hs and it didn't match up to the kaplan answers so I got sooo much more lost.

Thank you in advance 🙂

so you wanna go from fishcer projection to ....?

 

[Dentalicous1234]

to this type of projection where you show the arrangements in more 3D but here they have molecules just one carbon.

the molecule I explained above has 2 and it's throwing me off

 

[Dentalicous1234]

found a better image. You couldn't see the dashed lines as well in the other one. So basically just how do you go from the 2D version to one like this? I got mixed up.

I know that the groups on the dark solid lines come out at you
the dashed ones go back, behind the plane of the paper

but the order throws me off because you can't just use this and the fact that on the just lines diagram the horizontal ones come out at you and the vertical ones are back, behind the paper right?

i'm just getting confused, please help 😕

 

[Mstoothlady2012]

to this type of projection where you show the arrangements in more 3D but here they have molecules just one carbon.

the molecule I explained above has 2 and it's throwing me off

ok If i understand this right you want it in regular R & S form? I dont think I have done that before...i dont think its in destroyer either (unless I forgot😎)

Lets look at fischer projection first...can you assign them R & S config? IF you do, you will find that they both are R. Now you can put them in regular form (like you want) by giving wedges & dashes in such a way that when you assign priority they both form R

I hope that helps! try to do that if that still doesnt work let me know...

 

[Dentalicous1234]

first of all thank you so much for trying to explain it!! I am not sure if it's working though do you always just use R/S to tell if it's drawn from the 2-D to the right 3-D confis of fischer projections?

for example:
http://www.scienceaide.com/forums/viewtopic.php?t=158

in the image, basically how do you go from dash-wedge line structures to Fischer Projections. That's basically what the question is but instead of H's the kaplan question has all sorts of different substituents.
I tried using the color and dash/wedged outlined in that but it didn't work out the same.😕

 

[Mstoothlady2012]

first of all thank you so much for trying to explain it!! I am not sure if it's working though do you always just use R/S to tell if it's drawn from the 2-D to the right 3-D confis of fischer projections?

for example:
http://www.scienceaide.com/forums/viewtopic.php?t=158

in the image, basically how do you go from dash-wedge line structures to Fischer Projections. That's basically what the question is but instead of H's the kaplan question has all sorts of different substituents.
I tried using the color and dash/wedged outlined in that but it didn't work out the same.😕

ok I am confused again....

I thought you wanted to go from fischer to regular wedges & dashes (like the middle pic)..which is very easy to do.

I guess, now u wanna know how to backwards.... from dash-wedge to fischer right?

All you do is put the atoms that have wedges on the horizontal line and the atoms with dashes on vertical lines. IF you have solid line and you dont know what to do....change the atoms around & change the bonds as well...making sure that atoms stay connected to the same carbon where they were before. Keep in mind that the config should stay the same...so figure out dash-wedge structure config & make a fischer projection in such a way that you keep the config same and u dont interchange the atoms between 2 carbons.

 

[Dentalicous1234]

ok I am confused again....

I thought you wanted to go from fischer to regular wedges & dashes (like the middle pic)..which is very easy to do.

I guess, now u wanna know how to backwards.... from dash-wedge to fischer right?

All you do is put the atoms that have wedges on the horizontal line and the atoms with dashes on vertical lines. IF you have solid line and you dont know what to do....change the atoms around & change the bonds as well...making sure that atoms stay connected to the same carbon where they were before. Keep in mind that the config should stay the same...so figure out dash-wedge structure config & make a fischer projection in such a way that you keep the config same and u dont interchange the atoms between 2 carbons.

eeekk sorry I did mean how do you go from fishcer to dash-wedge. So I just use R/S and make sure they match like you explained before? arg I dunno why i'm getting lost with the kaplan example. maybe i've just been looking at it too much today. Will give that a rest and try it again tmrw. Please let me know if I can try looking at it a different way other than just look for R/S, that scienceaid example make it seem like you can gernalize the dash-wedges based on where they are, is this always true. i don't think so.

 

[Mstoothlady2012]

eeekk sorry I did mean how do you go from fishcer to dash-wedge. So I just use R/S and make sure they match like you explained before? arg I dunno why i'm getting lost with the kaplan example. maybe i've just been looking at it too much today. Will give that a rest and try it again tmrw. Please let me know if I can try looking at it a different way other than just look for R/S, that scienceaid example make it seem like you can gernalize the dash-wedges based on where they are, is this always true. i don't think so.

this is the only way that i know...sorry there might be another way but i cant help you with that coz I am unaware of it...any1else wanna help?

 

[predentlsu1]

I thought I had a pretty good handle on this before I looked at that question and read this thread lol. I took Advanced Organic last Fall and we did alot of stereochemistry realted problems. If I go home today I will look in my notes and try to find you a solid answer. At this point I am a little hazy on this as well.

 

[Dentalicous1234]

awww no sorry i confused ya but yea i am totally lost on that prob. still too

thank you guys so much for trying to help though! can't wait to sort this out and looking forward to reading how to solve it when you or someoen else posts some more insight cuz I am so worn out by this problem and it's just making me feel dumb now

ick silly kaplan!

 

[D.D.S.]

awww no sorry i confused ya but yea i am totally lost on that prob. still too

thank you guys so much for trying to help though! can't wait to sort this out and looking forward to reading how to solve it when you or someoen else posts some more insight cuz I am so worn out by this problem and it's just making me feel dumb now

ick silly kaplan!

Hey, This problem is tricky, but this is how I looked at it, and photoshopped something.. it works for me, so i hope it will work for you too.

Split the non fisher in two like I did, and then look at it from a differnt angle.
Since in the fisher projection, we want the bromine in the back, look at it from the bottom-behind. If you see it from there, the bromine will be in the back and the OH and D will be pointing towards you. But since you're looking at it from behind, you FLIP the molecule 180 degrees and you get the upper projection.

For the bottom portion of the non-fisher, look at it from a point where the F is going to be in the back just like the fisher. You can see that the OH and H will be pointing towards you on this one. ( the OH looks tricky, because from where i placed the eye, it looks as if the OH is pointing in the back because dash lines, but dont get confused because your point of view is differnt now) You dont have to flip this one 180 degrees, but just a little and you get that fisher.

Hope this helps. and doesnt confuse you further.