org. enantiomer

[myair]

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Can some one explain for me why Given a molecule 3S,4S ---- if the molecule is 3R, 4S than is that the diasterisomer which is true but When both are changed to 3R,4R then that is an enantiomer?

I think they are meso. Will some one give me an example plz?

thanks

 

[Sublimation]

Look at it this way, Chiral compounds have asymmetrical carbons. however, the definition of a chiral compound is one that its mirror image is not superimposable. therefore, the reason it can be chiral is because if you where to draw out a molecule that was R R and you found that it had a plane of symmetry making it achiral although it had asymetric carbons it will still be considered a meso compound. the way i do it is i draw out the fisher projection and look for a plane of symmetry. if you find one and you have a carbon or any other atom with 4 different ligands attached then it is a meso compound. i hope that helped

 

[myair]

if we have:


----- oH--OH
cH3---c---c---cH3
------ H---H

this is a meso I agree. It is 2S-3R.

if we change one of the compunds

------oH--OH
cH3---c---c---cH2CH3
------H--- H

This will be enantiomers? It is 2S-3R.
if it is not then how the enantimer will look like?

thank you 🙂

 

[myair]

Any explanation ?

 

[Sublimation]

if we have:


----- oH--OH
cH3---c---c---cH3
------ H---H

this is a meso I agree. It is 2S-3R.

if we change one of the compunds

------oH--OH
cH3---c---c---cH2CH3
------H--- H

This will be enantiomers? It is 2S-3R.
if it is not then how the enantimer will look like?

thank you 🙂

It wont be the enantiomer, because they are different compounds. anycompound that is meso it wont have an enantiomer. If you can recall from streochemistry, and molecule that has a line of symmetry ( regardless of R and S) and regardless if the molecule has a mirror image. Ill show you a easy way to determine the enantiomer of a fisher projection.

------oH--OH
cH3---c---c---cH2CH3
------H--- H
-------------------------------Mirror
------H--H
cH3---c---c---cH2CH3
-----OH---OH

Now if you take this mirror image and you rotate it 180 degrees. you will get

-----------oH--OH
cH2CH3---c---c---CH3
-----------H--- H

Which is different then the original image.
So if the mirror image, after you turn it 180 degrees, is different then the original molecule then the mirror image is the enantiomer. Dont let the meso compound confuse you, all a meso compound is, is a achiral molecule with an asymmetrical carbon.

 

[myair]

It wont be the enantiomer, because they are different compounds. anycompound that is meso it wont have an enantiomer. If you can recall from streochemistry, and molecule that has a line of symmetry ( regardless of R and S) and regardless if the molecule has a mirror image. Ill show you a easy way to determine the enantiomer of a fisher projection.

------oH--OH
cH3---c---c---cH2CH3
------H--- H
-------------------------------Mirror
------H--H
cH3---c---c---cH2CH3
-----OH---OH

Now if you take this mirror image and you rotate it 180 degrees. you will get

-----------oH--OH
cH2CH3---c---c---CH3
-----------H--- H

Which is different then the original image.
So if the mirror image, after you turn it 180 degrees, is different then the original molecule then the mirror image is the enantiomer. Dont let the meso compound confuse you, all a meso compound is, is a achiral molecule with an asymmetrical carbon.

Thank you it make many things clear for me 🙂