3.3.7 - Optical Isomerism Flashcards
What is a chiral (or asymmetric) carbon?
Carbon atom that 4 different groups has attached to it
What are optical isomers called?
enantiomers
Enantiomers are _______ ____ ____
non-superimposed mirror images
Draw 2-hydroxypropanoic acid and indentify its chiral centre
Draw the 2 enantiomers of 2-hydroxypropanoic acid
Plane-polarised light only vibrates in ___ direction
one
Optical isomers are optically active. What is meant by this?
They rotate plane-polarised light
Describe what happens when enantiomers rotate plane-polarised light
- One enantiomer rotates it in a clockwise direction
- & other rotates it in an anticlockwise direction
What does a racemic mixture contain?
Racemic mixture contains equal quantities of each enantiomer of an optically active compound
Racemates don’t show any ____ ______
optical activity
Why don’t racemates show any optical activity?
2 enantiomers cancel each other’s light-rotating effect
How do chemists get a racemic mixture of a chiral product? Explain why this works
- React 2 achiral things together
- ∵ when 2 molecules react there’s an equal chance of forming each of enantiomers
Explain how reacting butane and chlorine (2 achiral compounds) yields a racemic mixture of a chiral product
- Cl atom replaces on the H atoms
- Either H atom can be replaced so reaction produces mixture of 2 possible enantiomers
- Each H has 50-50 chance of being replaced = 2 optical isomers formed in equal amounts
What is the disadvantage of using chemical methods to modify a reaction to produce a single enantiomer?
It’s difficult and expensive
Doubles bonds (C=O and C=C) are _____
planar (flat)