Isomerism Flashcards
What are the two types of isomerism?
strucutral isomerism
stereoisomerism
What can stereoisomerism be split into?
geometric isomerism
optical isomerism
What is meant by structural isomers?
Molecules with the same molecular formula but different structural formula
What are stereoisomers?
molecules with the same molecular formula with a different spatial arrangement of their atoms. Thet are non-superimposable.
When does geometric isomerism occur?
in molecules where there is no free rotation about the carbon to carbon bond
What does ‘cis’ mean?
on the same side of the fixed bond
What does ‘trans’ mean?
on the opposite side of the fixed bond
What do geometric isomers sometimes differ in?
their physical and chemical properties
Why do some geometric isomers differ in their physical and chemical properties?
due to differences in their ability to pack together
What are optical isomers?
non-superimposable mirror images of each other
What are molecules which have no symmetry said to be?
chrial
If asked to draw an optical isomer, what must you always draw along withit?
the original isomer
What are optical isomers also known as?
enantiomers
What is a racemic mixture?
a mixture of equal quantities of enantiomers
What does light passing through a polarisiting filter vibrate in?
one plane only
What hapeens when polarized light passes through a solution containing an optical isomer?
the polarized light is rotated
What can the direction of rotation be?
right or left
What name is given if the direction of rotation is right?
dextrotatory
What name is given if the direction of rotation is left?
laeveorotatory
In terms of plane polarised light (ppl), what will enantiomers do?
rotate pple by equal and opposite amounts
What effect does a reacemic mixture have on ppl?
it is optically in active and has no effect on ppl
What is the angle of rotation denoted by and what is it measured in?
theta and in degrees
State 3 properties of optical isomers.
- same physical properties i.e. melting/boiling point
- are often present in equal proportions (racemic mixtures)
- same chemical properties, except when in a chiral environment i.e. when other chiral molecules are present
How many optical isomers are normally present in living things?
1
What are many medicines and why is this the case?
racemic mixtures because it is too costly to separate the isomers
e.g. Salbutamol - one form is more pharmacologically active
Thalidomide - one enantiomer damaged the unborn baby
