Stereoisomerism Flashcards
What are the two types of isomerism?
Structural isomerism and Stereoisomerism
What are the types of structural isomerism?
- Functional group isomerism
- Chain isomerism
- Position isomerism
What is functional group isomerism?
Same molecular formula different functional groups
What is position isomerism?
Same molecular formula but different positions of functional groups
What is chain isomerism?
Same molecular formula but different carbon chain arrangement (e.g. varying methyl groups)
What are the types of stereoisomerism?
- Geometrical isomerism (E/Z)
- Optical isomerism (R/S)
What does E/Z refer to?
Z - means Cis / same side
E - means Trans / opposite side
What do all geometric molecules have?
At least one double bond
How do you decide what groups determine whether a molecule is E/Z isomerism?
The two groups must the longest carbon chain or highest priority group (e.g. -OH higher than -Br)
What does R/S refer to?
R - Clockwise
S - Anticlockwise
How do we know if a molecule is chiral or not?
The carbon will have 4 different functional / carbon groups attached to it
This carbon will be known as the chiral centre
How do we decide what order the atoms are arranged in when determining chirality?
- 1 will be at the top - This is the atom with the highest atomic number
- 2 is the atom with the second highest atomic number etc..
- 2 will be towards the left and 4 will be towards the right when the isomer is Anticlockwise (S)
- 2 will be towards the right and 4 will be towards the left when the isomer is Clockwise (R)
What are two of the same optical isomers called?
Enantiomers
What is a mixture called containing 50:50 enantiomers?
Racemic mixture
How do we distinguish between enantiomers?
Polarimetry:
1. Shine a plane of polarised light through a sample
2. Each enantiomer will rotate the light in the opposite direction
3. To the left ( l / - ) or to the right ( d / + )
4. + and - aren’t related to R/S
