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newman projection

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joonkimdds

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choose the true statment.
a) this is meso
b) this is (2S, 3S).
c) this is chiral
d) specific rotation is above 0 degree.
e) this is (2R,3R).

I think the answer key says A but I am not sure about this.

if this is meso, can someone teach me how to draw newman projection like this in a plane sheet of paper so I can tell whether it has internal symmetery or has S or R orientation?
I have tried many times and not sure which one is correct way of drawing among
......Br
...H-C-CH3
CH3-C-H
.......Br

and
......Br
CH3-C-H
CH3-C-H
.......Br

and
......CH3
...H-C-Br
CH3-C-H
.......Br

and so on.
 

sajjy

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123.jpg

choose the true statment.
a) this is meso
b) this is (2S, 3S).
c) this is chiral
d) specific rotation is above 0 degree.
e) this is (2R,3R).

I think the answer key says A but I am not sure about this.

if this is meso, can someone teach me how to draw newman projection like this in a plane sheet of paper so I can tell whether it has internal symmetery or has S or R orientation?
I have tried many times and not sure which one is correct way of drawing among
......Br
...H-C-CH3
CH3-C-H
.......Br

and
......Br
CH3-C-H
CH3-C-H
.......Br

and
......CH3
...H-C-Br
CH3-C-H
.......Br

and so on.

alright...i will try to explain this 3D stuff here.....this is what i follow...
i always use fischer projection and it makes it clear....try to follow these steps-:
Keep the carbons in the straight line of the fischer projection
which means that both terminal carbon (methyl in this case) will be going away from you in the fischer projection
in Newmann projection, rotate the c-c bond so that both methyl group are towards the bottom side in eclipsed position.
when you will draw the newmann projection with methyl on bottom sides, both Br will come on one side, and in this case on the left side....
if you try to make fischer projection of this newmann projection, then u will have
......CH3
Br---C---H
Br---C---H
.......CH3
here both methyl are going away from you while Br and H coming towards you.....
try to visualize this fischer projection and compare it with Newmann projection

And it has a plane of symmetry or do the mirror test and this will be a meso compound.
Hope that helps
 

dontwakeme

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123.jpg

choose the true statment.
a) this is meso
b) this is (2S, 3S).
c) this is chiral
d) specific rotation is above 0 degree.
e) this is (2R,3R).

I think the answer key says A but I am not sure about this.

if this is meso, can someone teach me how to draw newman projection like this in a plane sheet of paper so I can tell whether it has internal symmetery or has S or R orientation?
I have tried many times and not sure which one is correct way of drawing among
......Br
...H-C-CH3
CH3-C-H
.......Br

and
......Br
CH3-C-H
CH3-C-H
.......Br

and
......CH3
...H-C-Br
CH3-C-H
.......Br

and so on.


meso.png


2 chiral centers, same substituents, opposite stereochem. config = Meso
 

joonkimdds

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wow...LOL.
Thanks you guys so much for hard work!
I guess the main reason I got confused is that they are staggered and anti so I thought that they should be something like
......Br
...H-C-CH3
CH3-C-H
.......Br
so that CH3 and another CH3 look like anti and 180 degree apart (even though it should be 60 degree in fischer projection).

Anyway everything is clear now. Thanks again.
 

Imperium

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Just remember that single bonds can be rotated to fit the configuration easiest for you to visualize.
 

rose786

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meso.png


2 chiral centers, same substituents, opposite stereochem. config = Meso

How did you know which substituents were on the dash or wedge?

Like with Fisher projections, horizontal lines represent substituents coming out of the page. Is there a similar rule for Newman projections?
 

dontwakeme

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The ones on the same side of the newman projection are on wedge. The ones on the other side are on dash. You can reverse it, doesn't really matter. The Bromine positions are on stick.. This configuration matches the newman because the CH3's are anti, the H's are anti, and the Br's are anti.
 

rose786

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The ones on the same side of the newman projection are on wedge. The ones on the other side are on dash. You can reverse it, doesn't really matter. The Bromine positions are on stick.. This configuration matches the newman because the CH3's are anti, the H's are anti, and the Br's are anti.

Ok cool. I had to draw out it out to see what you meant.
 
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