Optical Isomerism Flashcards
(16 cards)
What type of isomerism is “optical isomerism?”
- Stereoisomerism.
What is the essential requirement for optical isomerism to occur?
- Molecule must have a chiral centre.
What type of carbon atom gives rise to optical isomers?
- Asymetric, chiral carbon atoms.
What is a chiral molecule?
- Molecule that contains a C atom bonded to 4 different groups (4 SINGLE bonds.)
() - extra info for clarification.
What are “enantiomers?”
- Isomers that exist as non-superimpossable (ie. won’t overlap) mirror images of one another.
() - extra info for clarification.
How can two enantiomers be distinguished from one another?
- Will rotate plane polarised light.
- Equal amounts, in opposite directions (ie. one clockwise, other anti-clockwise.)
() - extra info for clarification.
What will optically-active isomers do to plane-polarised light?
- Rotate plane-polarised light.
Why are racemates/ racemic mixtures optically inactive?
- Plane polarised light will not be rotated at all.
- 2 enantiomers rotate light in opposite directions by same amount so they cancel out.
What is a racemic mixture/ racemate?
- A mixture of equal amounts of enantiomers.
True or False
It is easy to separate a mixture of enantiomers to leave you with 1 enantiomer.
- False.
- It can be very difficult/ expensive to separate a mixture of enantiomers.
Why are enantiomers formed in equal amounts during reaction between CH3CHO and HCN?
(diagram of this on Gautum notes.)
- There is a trigonal planar arrangement around the 2nd C in CH3CHO.
- This means there is an equal probability of the CN- attacking from above/ below the trigonal planar group.
Why do we pass light through a polaroid filter and THEN through the sample?
- Produces plane polarised light, only oscilates in one direction whereas, standard light oscilates in all directions.
How is a racemic mixture of chiral product often made?
- By reacting achiral substances together.
What molecules can react to produce racemic mixtures?
- Molecules with (trigonal) planar sections.
- Attack on C=O of unsymmetrical ketones and all aldehydes (other than methanal.)
In racemic mixtures, why do we have the same amount of each enantiomer?
- When molecules react, there is an even chance of forming each enantiomer.
What is another word for a chiral carbon atom?
- Asymetric carbon atom.
