Stereochemistry

Question 1

What is an enantiomer?

Answer 1

An enantiomer is a stereoisomer that is the nonsuperimposable mirror image of another molecule

nonsuperimposable - rotating around sigma bonds does not create the same molecule

Question 2

What is a diastereomer?

Answer 2

A diastereomer is also a stereoisomer, but is not a mirror-image of another molecule. Cis and trans stereoisomers of the same molecule are diastereomers, also, if a molecule has multiple chiral centers, diastereomers can be determined from the R/S designation for each chiral center.

i.e.

Question 3

What is a constitutional isomer?

Answer 3

Constitutional isomers have the same molecular formula (same number and identity of atoms) but will have different connectivity (configuration)

Question 4

T/F : The physical properties of enantiomers are the same

Answer 4

True

i.e. the melting point and boiling points of enantionmers are identical

Question 5

T/F : The physical properties of diastereomers are the same

Answer 5

False

i.e. the melting point and boiling points of diastereomers can differ significantly

Question 6

What is an asymmetric carbon?

Answer 6

A carbon that is attched to four different substituent groups/atoms

Question 7

For the Cahn-Ingold Prelog system, does the lowest priority group point forward (wedge) or backward (dash)

Answer 7

The lowest priority group (commonly hydrogen) will be projecting backwards (dashed bond) to assign R/S. If the lowest priority group is projecting forward (has a wedged bond) then flip the R/S assignement.

Question 8

What are stereoisomers?

What are the sub-classes of stereoisomers?

Answer 8

Molecules that have the same connectivity but different spatial arragnements. The configuration of the atoms in each molecule will be identical, but their conformation will be different.

Enantiomers and diastereomers/alkene isomers

Alkene isomers are a type of diastereomer

Question 9

Will reversing the wedged/dashed bonds form an enantiomer?

Answer 9

No, it would be the same molecule. This is known as mesoform.

Question 10

Will writing this molecule with wedged bonds instead of dashed form an enantiomer?

Answer 10

Yes, there is no plane of symmetry in this molecule. Rotating across the C2-C3 bond we can see that there will be an enantiomeric form if the bonds are switched in conformation.

Question 11

Will reversing the wedged/dashed bonds form an enantiomer?

Answer 11

No, it would be the same molecule. This is known as mesoform.