Any tricks on how to handle Enantiomers, Stereogenic?

[blankguy]

reading ahead on OChem. This seems to be tricky on how to figure out if a molecule has enantiomers. How to tell if a carbon is stereogenic(how to rotate it so it shows different enantiomers)? My eyes are not functioning properly.

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[justletmein]

just write out the fischer projections and find R and S at each chiral carbon and compare! if they're different at each carbon, ex. R,R then S,S then you've got enantiomers! might have a meso compound though so watch out!

 

[blankguy]

meso compound being the same compound looked at different angles right??

 

[blankguy]

MESO means that there is an internal plane of symmetry, therefore the ENTIRE MOLECULE is ----------> ACHIRAL!!!!!!!!!!!!!!!

I've been monkeying around building 3d models and I still don't quite get it with this enantiomers. The molecule I've been playing around with is 3-methylpentane which has no enantiomers. I'm trying to understand why.


This whole subject makes me feel like I need an eye exam

AAAAARRRRRRRGGGGGGGHHHHHHHH!!!!!!
Me and my 3d models----->Zoolander scene where Stiller and Owen are banging away at the iMac. "The file is in the computer!"

 

[phosphorylation]

MESO means that there is an internal plane of symmetry, therefore the ENTIRE MOLECULE is ----------> ACHIRAL!!!!!!!!!!!!!!!

the big thing about meso compounds though, is that they have no optical activity.

 

[isd121]

The molecule I've been playing around with is 3-methylpentane which has no enantiomers. I'm trying to understand why.

Molecules that are non-superimposable mirror images are enantiomers. There must be a Chiral carbon (a chiral carbon atom have four different groups attached to it) in a molecule to form a non-superimposable mirror image. In case of 3-methylpentane, the 3rd cabon is attached to H, methyl and two ethyls. so it is not a chiral cabon; means no enantiomers.
hope this will help

 

[blankguy]

Okay reread this section.
Racemic vs meso
Meso no optical activity
Racemic equal moles of + and - thus canceling each other.
How does one find the optical activity of a pure substance?

Reread the stereogenic carbon bit and played with molecules like 2-bromobutane, and 2-methylbutanol. Switching the functional groups at the second carbon and reorienting the molecule so that the functional groups are oriented in a similar fashion as before. If the bromo was in the left then after the switch I would turn the entire molecule around so that the bromo would be on the left and see if the other carbons are connected in the same way(sticking forward or are on the back).

How about 2-methylpentanol? I think this has symmetry running along the main carbon chain.

 

[blankguy]

BLANKGUY,
Please answer this one, it is a little more tricky to determine chirality:

DOES 1-chlorocyclopentan-1-ol HAVE A STEREOGENIC CENTER?
- Please describe your answer

I'll let you know if you got it right or wrong-- if someone else doesn't beat me to the punch (I love this stuff!!!)

I don't believe it does. If the 5 carbon ring is flat it will the same molecule if you swap the alcohol group with the chlorine atom, or one of the connectons to the ring. BTW shouldn't the name be something like 1-chlorocyclopentanol?