Topic 3: Stereoisomers and Chirality pt 4

Question 1

Compounds with More than 1 Chirality Center

Answer 1

Maximum # of isomers is 2^n, where n=the # of chiral carbons

Question 2

Meso Compounds

Answer 2

The 2^n rule will not apply to compounds that may have a plane of symmetry.

*Top side of mirror image of bottom side.

Must have a plane of symmetry through the middle of it

*They are achiral (since it has a axis of symmetry and does not rotate plane-polarized light)

Question 3

Diastereomers: Cis-trans Isomerism on Double Bonds

Answer 3

Stereoisomers not mirror images of one another. Not enantiomers are diastereomers.

Question 4

Diastereomers: Cis-trans Isomerism on Rings

Answer 4

Cis-trans isomers do not mirror images so diastereomers.

Question 5

Diastereomers

Answer 5

-2 molecules or more chiral carbons
-Are NOT mirror images

Question 6

Two or More Chiral Carbons

Answer 6

**When they have 2 or more chiral atoms you have three options, “enantiomers, diastereomers or meso”

-Enantiomers: opposite configuration (R or S) corresponding chiral carbon.

-Diastereomers: Some matching, some opposite configurations

-Meso Compounds: Have internal mirror planes

Maximum number of isomers is 2^n, where n=the number of chiral carbons.

Question 7

Summary

Answer 7

If 2 otherwise identical molecules have more than one stereo center in them, then one of the three situations can occur:

1.Same R,S configurations at every single stereo center = Same

2.Opposite R,S every single sterocenter = Enantiomers

3.If they are any where in-between= Diastereomers

Question 8

Properties of Diastereomers

Answer 8

-Diastereomers have different physical properties, easily separated
-Differ only in reactions with chiral molecules, polarized light
-Enantiomers are difficult to separate
-Convert Enantiomers to diastereomers then they are able to separate

Question 9

Resolution of mixture into Separate enantiomers

Answer 9

Enantiomers are difficult to separate since they have the same boiling point… utilize the different physical diastereomers

1. Formation of diastereomeric salts. A racemic mixture of anions allows to form of salts with pure cation enantiomers (After the separation of the diastereomers, the enantiomer’s pure acids are recovered by the addition of an achiral acid)
2. Racemic mixture is put through a column packed with chiral material. One enantiomer passes through more quickly.
3. Racemic mixture reacted with chiral enzymes. One enantiomer is selectively reacted.