Unit 2-Stereochemistry Flashcards
What are structural isomers?
Compounds with same number of atoms but bonded together in a different order
Example propan-1-ol and propan-2-ol
What structural feature causes geometric isomers to arise?
They arise due to the lack of free rotation around a bond, frequently a carbon–carbon double bond, but not always.
Could be ring structure (cycloalkanes)
For geometric isomers explain the prefixes cis and trans.
cis means “on the same side” of the carbon to carbon double bond
trans means “on different sides” of the carbon to carbon double bond
What are the names of these two geometric isomers?
cis-but-2-ene
trans-but-2-ene
Explain why propene does not exhibit geometric isomerism?
Geometric isomers can only occur in organic molecules which have two different groups attached to each of the carbon atoms of the double bond, in addition to the carbon to carbon double bond.
Name the following structures.
cis-1,2-dichlorocyclopropane
trans-1,2-dichlorocyclopropane
What structural feature causes optical isomers to arise?
Contains a chiral centre/chiral carbon
What is meant by a chiral carbon?
Carbon attached to 4 different groups.
What are enantiomers?
Non superimposable mirror image molecules.
Enantiomers have an effect on plane polarised light.
What does plane polarised light mean?
Light that has been filtered so that it only vibrates in one plane.
Enantiomers are said to be optically active.
What does this mean?
One enantiomer will bend plane polarised light in a clockwise direction (sometimes shown using +), the other enantiomer will bend plane polarised light in an anticlockwise direction (sometimes shown using -).
What is a racemic mixture?
A mixture containing equal quantities of both enantiomers
