A-level Chemistry: 3.3.7 Optical Isomerism
This set of flashcards covers the concept of chirality, focusing on chiral (asymmetric) carbon atoms, optical isomers (enantiomers), and their properties. It also includes examples like 2-hydroxypropanoic acid, highlighting its chiral center and the behavior of plane-polarized light with enantiomers.
What is a chiral (or asymmetric) carbon?
Carbon atom that 4 different groups has attached to it
Key Terms
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
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| Term | Definition |
|---|---|
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? | |
Describe what happens when enantiomers rotate plane-polarised light |
|
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 |
|
Explain how reacting butane and chlorine (2 achiral compounds) yields a racemic mixture of a chiral product |
|
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) |
When is a racemate formed in a reaction mechanism? | When reactant or intermediate has a trigonal planar group in molecule is approached from both sides by an attacking species e.g. Nucleophilic addition of HCN to aldehydes and ketones (unsymmetrical) |
Draw the 1st stage of the mechanism for the reaction of propanal with acidified potassium cyanide (KCN) | |
When propanal is reacted with acidified potassium cyanide (KCN), why is there an equal amount of each enantiomer formed? | C=O bond is planar = equal chance that nucleophile will attack from above the plane of the molecule or from below it |
Why does the product(s) of nucleophilic addition of HCN to symmetrical ketones not display optical isomerism? | Make a product that doesn’t have a chiral centre |
Name another mechanism where a racemate can be formed |