Chirality 1 & 2 Flashcards
What are stereoisomers?
Isomers with same molecular formula + same connectivity of atoms BUT different spatial arrangement
Describe constitutional isomerism
Molecules with same formula but different connectivity
What can constitutional isomers not do?
Interconvert
What are examples of constitutional isomers?
Aspirin
Caffeic acid
4-hydroxyphenyl-pyruvic acid
What is geometric isomerism?
Cis + trans
Same formula, same connectivity of C skeleton but different spatial arrangement of substituents around alkane
What is cis?
Same face
What is trans?
Opposite faces
When is there no interconversion between cis + trans?
At ambient or body temp
What temp is required for cis + trans interconversion?
180 degrees
What is the cis form of C4H4O4?
Maleic acid
What is the trans form of C4H4O4?
Fumaric acid
What is the Cahn-Ingold-Prelog naming system?
Prioritise 2 substituents according to their atomic number of atom directly attached to C
What is it if priority groups 1 are on same face?
Z
What is it if priority groups 1 are on opposite faces?
E
What does stereoisomers normally have?
Chiral C
What is a chiral carbon?
Stereocentere = stereogenic C
What is optically inactive?
Achiral
What is a racemic mixture?
1:1 mix of enantiomers
What happens if it is a mirror image?
Non-superimposable
What is hybridisation state of chiral C?
sp3
If it is superimposable what it is?
Achiral
if it is non-superimposable what it is?
Chiral
What is the non-superimposable mirror image called?
Enantiomers
What can a carbohydrate be?
D or L
If the OH in a carbohydrate is to the left, what is it?
L
If the OH in a carbohydrate is to the right, what is it?
D
Can amino acids be D or L?
YES
What are most amino acids in proteins?
L
How do you determine of an amino acid is L or D?
Position of amine group
How do you use Cahn-Ingold-Prelog naming system for chiral C?
Prioritise groups around C with lowest priority going away from you
If Cahn-Ingold-Prelog naming system for chiral is clockwise order what do you name it?
R
If Cahn-Ingold-Prelog naming system for chiral is anti-clockwise order what do you name it?
S
What is the dashed line mean in drawing out chiral C?
Group is behind C
What happens if priority 4 is at the front instead?
Viewing molecule from opposite side
= reverse answer
= clockwise really anti-clockwise
What must we do if priority 4 is not at the back?
Must rotate molecule
What do R + S isomers of a molecule have?
Identical physical + chemical properties
How is plane polarised light produced?
By passing light through polarising filter
What does each optically active compound have?
Character specific rotation
What is a racemic mixture than contains equal amount of 2 enantiomers?
Optically inactive
What is enantiomer excess (ee)?
Amount of enantiomer in excess of racemic mixture
What happens if ee is 50%?
Then the observed rotation will only be 50% of the rotation of the pure enantiomer
How can ee be calculated?
Observed specific rotation
—————————————————- X100
specific rotation of pure enantiomer
What do R enantiomers do?
Bind correctly = trigger response
What do S enantiomers do?
Cannot bind correctly = do not trigger response
Describe Vigabatrin
S-enantiomer active as anti-convulsant
Inhibits inactivation of GABA by GABA transaminase
Increases levels of GABA = reduces seizures
How do you name when more than 1 stereogenic centre?
Number the S + R centre
What happens if the molecule has an internal plane of symmetry?
Meso compound
