KA2: Stereo chemistry Flashcards
what is an isomer?
molecules that have 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 does stereoisomers occur?
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 stereo isomer?
-geometric
-optical
when can 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 can optical isomers occur?
in compounds in which four different groups are arranged tetrahedrally around a central carbon atom (chiral carbon or chiral centre)
describe the properties of geometric isomers
-differences in physical properties, such as melting point and boiling point
-can have differences in chemical propetties
what must geometric isomers have?
two different groups attached to each of the carbon
atoms that make up the bond with restricted rotation
what can geometric isomers be labelled as?
cis or trans according to whether the substituent
groups are on the same side (cis) or on different sides (trans) of the bond with restricted rotation
optical isomers are…
…asymmetric and are non-superimposable mirror images of each other
what can optical isomers be described as?
enantiomers
describe the properties of optical isomers
-identical chemical properties, except when in a chiral environement such as that found in biological systems (only one optical isomer is usually present)
-have identical physical properties, except for their effect on plane-polarised light
what does optically active mean?
rotate plane-polarised light by the same amount but in opposite directions
what is a racemic mixture?
when mixed in equal amounts are optically inactive because the rotational effect of the plane-polarised light cancels out
