7. Stereoisomers Flashcards
What are the two types of stereoisomers?
Enantiomers (mirror image)
Diastereomers (non mirror image)
What are the two types of diastereomers?
Configurational diastereomers
Cis-trans diastereomers
What does chiral mean?
- Moelcules that possess non-superimposable mirror images are chiral
- They do not contain a plane of symmetry
Do enantiomers have the same properties?
Enantiomers have identical physical and chemical properties (with some exceptions)
What is an asymmetric centre?
Another name for chiral centre or stereogenic centre
- An sp3 hybridised carbon with four different groups attached
What are the two ways enantiomers can be differentiated?
- They differ in the way they interact with other chiral molecules
- They differ in the way they interact with plane polarised light
What are the steps to assigning an R or S descriptor?
- Rank the four substituents
- Determine clockwise or anticlockwise sequence
- Assign R or S
What is the first rule of assigning priority?
Prioritise substituents in decreasing order of the atomic number of the atom directly attached
What is rule 2 of assigning priorities?
If two directly attached atoms are the same, compare the second atoms in each group
What is the third rule of assigning priorities?
Treat multiple bonds as the equivalent number of single bonds
What is the fourth rule of assigning priorities?
View the molecule so that you are looking down the bond from carbon to group 4
What is a race mic mixture?
AN equal mix of enantiomers
What is the formula for working out number of asymmetric centres?
-a molecule with n asymmetric centres has a (maximum) of 2^n stereoisomers
What are diastereomers?
Stereoisomers that are not enantiomers
Difference between enantiomers and diastereomers?
- All asymmetric centres of opposite configuration gives enantiomers
- All asymmetric centres of the same configuration, at least one opposite gives diastereomers
