isomerism Flashcards
structural isomerism
same molecular formula but different structural formula
chain - length of c chain
position - position of functional group
functional group - type of functional group
stereoisomerism
same structural and molecular formula but have different arrangement of atoms in space
e/z and optical isomerism
how e/z isomers arise
each carbon has to be bound to 2 different groups in c=c bond
there is restricted rotation around the c=c bond
e/z isomers
e isomers - higher priority on opposite sides
z isomers - higher priority on the same side
optical isomerism key points
optical isomerism can occur when a carbon atom bonds to four different groups
carbon centre with 4 different groups bonded - chiral centre
forms 2 isomers - mirrors images
pair of enantiomers
what is optical isomerism
optical isomerism rotate the plane of polarised light
one isomer will rotate it clockwise the other isomer will rotate it anti clockwise in opposite direction
optically inactive
if both isomers present in a sample no rotation will be seen
as 1 rotates clockwise the other rotates anticlockwise by the same amount
optical isomers will have a number of similar properties
-same mp and bp
-same solubility in a range of solvents
-same mr
-same peaks in their mr spectrums
racemic mixture
a sample that has both optical isomers in equal amounts
enantiomer
single optical isomer
enantiomerically pure
a sample that has 1 optical isomer
thalidomide
drug developed in 1950s to relieve morning sickness in pregnant women
R optical isomer had desired effect
S optical isomer thought to have no effect
so drug was given as a racemic mixture
S isomer caused physical defects in unborn baby
when producing a new drug there are three options
-supply drug as racemic mixture
runs the risk of unwanted side effects caused by other isomer
even if theres no side effects half the drug is ineffective which is wasteful and inefficient
-make the drug as a racemic mixture then separate out the two isomers
challenging as isomers are similar and few methods are available to separate them
–find a method synthesis in which only one enantiomer is formed
challenging but many starting materials which come from plants form in nature as single enantiomers so using one of these can ensure only 1 enantiomer is formed