Stereo Chemistry Flashcards
What are structural isomers?
Structural isomers occur when the atoms are bonded together in a different order in each isomer
What are stereoisomers?
Stereoisomers occur when the order of the bonding in the atoms is the same but the spatial arrangement of the atoms is different in each isomer
What are the two types of stereoisomer?
Geometric and optical
When will geometric isomers occur?
When there is restricted rotation around a carbon=carbon double bond or a carbon-carbon single bond in a cyclic
compound
When will a geometric isomer be labelled as cis?
The substituent groups are on the same side
When will a geometric isomer be labelled as trans?
The substituent groups are on different sides
Describe how chemical and physical properties vary in geometric isomers.
- HAVE differences in physical properties, such as melting point and boiling point
- CAN HAVE differences in chemical properties
When will optical isomers occur?
In compounds in which four different groups are arranged
tetrahedrally around a central carbon atom (chiral carbon or chiral centre)
Optical isomers…
- are asymmetric
- are non-superimposable mirror images of each other
- can be described as enantiomers
Describe how chemical and physical properties vary in optical isomers.
- have identical physical properties, except for their effect on plane-polarised light
- have identical chemical properties, except when in a chiral environment such as that found in biological systems (only one optical isomer is usually present)
How do optical isomers affect plane-polarised light?
Rotate plane-polarised light by the same amount but in opposite directions and so are optically active
What happens when optical isomers are mixed in equal amounts?
Become optically inactive because the
rotational effect of the plane-polarised light cancels out, this is called a racemic mixture
