Stereo chemistry Flashcards
What are isomers?
molecules with the same molecular formula but different structural formulae
When do structural isomers occur?
when the atoms are bonded together in a different order in each isomer
When do 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
What compounds do geometric isomers occur in?
compounds with:
restricted rotation around a C=C double bond or a C-C single bond in a cyclic compound
two different groups attached to each of the C atoms that make up the bond with restricted rotation
What are cis and trans geometric isomers?
cis-substituent groups are on the same side of the bond with restricted rotation
trans-substituent groups are on different sides of the bond with restricted rotation
What differences do geometric isomers have?
in physical properties (eg mp and bo) and in chemical properties
What compounds do optical isomers occur in?
compounds that:
have four different groups arranged tetrahedrally around a central C atom (chiral carbon/chiral centre)
are asymmetric
How can optical isomers be described?
non-superimposable mirror images of each other
enantiomers
What differences do optical isomers have?
identical physical properties except their effect on plane-polarised light
identical chemical properties except when in a chiral environment such as that found in biological systems (only one optical isomers is usually present)
what do optical isomers do to 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?
they are optically inactive because the rotational effect of the plane-polarised light cancels out
this is called a racemic mixture
