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The single most important rule regarding Fisher projections is that 90 degree rotations are not allowed since it produces an enantiomer of the original molecule.. My question is how is an enantiomer of the original molecule being produced ??? The resulting molecule produced by the 90 degree rotation of a molecule is a non-superimposable molecule(which cannot be superimposed on the original molecule) but it is not a mirror image of the original molecule & enantiomers are NON-SUPERIMPOSABLE MIRROR IMAGES ?? Then too it is said that a rotation of 180 degree of a molecule gives back the same molecule but the ans is No !!! Then a rotation of 270 degree gives a enantiomer(again) of the original molecule but how??? Pls post ur reply and help me in my preparation!!! God bless you Your answers are always gonna be approved!!!

The single most important rule regarding Fisher projections is that 90 degree rotations are not allowed since it produces an enantiomer  of the original molecule..


My question is how is an enantiomer of the original molecule being produced ???


The resulting molecule produced by the 90 degree rotation of a molecule is a non-superimposable molecule(which cannot be superimposed on the original molecule) but it is not a mirror image of the original molecule & enantiomers are NON-SUPERIMPOSABLE MIRROR IMAGES??


Then too it is said that a rotation of 180 degree of a molecule gives back the same molecule but the ans is No !!!


Then a rotation of 270 degree gives a enantiomer(again) of the original molecule but how???


 


Pls post ur reply and help me in my preparation!!!


God bless you


Your answers are always gonna be approved!!!

Grade:12

2 Answers

SAGAR SINGH - IIT DELHI
879 Points
10 years ago

Dear student,

Fischer Projections are abbreviated structural forms that allow one to convey valuable stereochemical information to a chemist without them having to draw a 3D structural representation of a molecule. These representations are only used for molecules that contain stereogenic centers, which are then represented as simple crosses.

A Fischer representation

They can be derived by considering the more accurate 3D representation using wedges and assuming the convention that horizontal lines represent bonds coming out of the plane of the paper and vertical lines represent bonds going behind the plane of the paper.  

revealing the stereochemistry of a Fischer diagram

Geoffrey Richards
34 Points
10 years ago

Sorry Sagar, but that was not the ans i wanted !!!

U see my question basically is that when u rotate a molecule represented by  fisher projection by 90 degree (which is actually not allowed) it is said that u get an enantiomer of the molecule considered.

My question here is how is it so??

I argue that enantiomers are MIRROR IMAGES  which are NON-SUPERIMPOSABLE !!!     

But what u get by rotating the given molecule by 90 degree is another non-superimposable molecule which cannot be superimposed on the given molecule . okay. But the new molecule that is formed by the rotation of the Given molecule by 90 degree is not a mirror image of the original molecule !!!

But enantiomers are non-superimposable MIRROR IMAGES  !! of the given molecule so how can this be possible that by rotating a molecule by 90 degree u get its enantiomer ???

 

Explain that to me clearly and i will give u a speedy approval .!!

Thank you anyway !!

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