8. Stereochemistry

what are isomers

molecules that have the same molecular formula but different structural formulae

what are stereoisomers

molecules with the same molecular formula and the same structural formula but different shapes

how 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 types of stereoisomer are there

geometric

optical

how can geometric isomers occur

when theres restricted rotation around a C=C double bond or C-C single bond in a cyclic compound

how many different groups must geometric isomers have attached to each carbon

2 with restricted rotation

how can geometric isomers be labelled

cis

trans

what does cis mean

same side of the bond with restricted rotation

what does trans mean

different sides of the bond with restricted rotation

what differences can geometric isomers have

physical properties, such as melting point and boiling point

can have differences in chemical properties

how do optical isomers occur

in compounds in which 4 different groups are arranged tetrahedrally around a central carbon atom

what can compounds with 4 different groups attached to a carbon be called

chiral

are optical isomers symmetrical or asymmetrical

asymmetrical

what do optical isomers look like

non-superimposable mirror images of each other

what can optical isomers be described as

enantiomers

what kind of physical properties do optical isomers have

identical physical properties, except for their effect on plane-polarised light

what kind of chemical properties do optical isomers have

same except when in chiral environments such as those found in biological systems (only 1 optical isomer is usually present)

how do optical isomers rotate plane-polarised light

by the same amount but in opposite directions

what term is used to describe how optical isomers rotate plane-polarised light

optically active

how can optical isomers be optically inactive

when mixed in equal amounts

why can optical isomers be optically inactive

the rotational effect of the plane-polarised light cancels out

what term is used for when optical isomers are optically inactive

racemic mixture