optical isomerism Flashcards
isomerism is when
more then one compound has the same molecular formula (number of atoms of each element) but different arrangement of atoms in space
one type of isomerism is structural. this is
when molecules have the same molecular formula but different structural formula
position
chain length
functional group
one type of isomerism is steroisomerism. this is when
molecules have the same molecular unstructural formula but the 3D orientations of the atoms in space is different
geometric (c=c bonds so restricted rotation and each c in the bond has two different groups bonded to them)
and optical
optical isomerism is
a type of stereoisomerism where the molecules have the same molecular and structural formula but different spatial arrangement of atoms in space, occurring when there is an asymmetrical carbon within a molecule known as a chiral centre
chiral carbon centre
c atom with four different groups bonded to it
why does a chiral centre result in optical isomerism
optically active meaning
there is no line of symmetry in the molecule. this means the mirror image of the molecule is non-superimposable and therefore a different molecule
molecules with a chiral carbon and a non-suprimposable mirror image are described as optically active
enantiomers
the different forms (isomers) of the same molecule produced by optical isomerism
distinguished by +/-
racemate/ racemic mixture
mixture whrein the ratio of enantiomers is 1:1
50/50
enantiomers have identical chemical and physical properties except for in what two cases
their effect on plane polarised light
so you can test for them by doing these things
what is plane polarised light
light is an electromagnetic wave. made up of vibrations. the electronic vibrations and magnetic vibrations are perpendicular to eachother
when light is passed through a material where the vibrations apart from those in one plane (direction) is stilled, this produces plain polarized light
what happens when you shine plane polarised light through an enantiomer mixture
you can determine which an enantiomer it is because the plane of polarization rotates from vertical in an anti-clockwise position
so - enantiomer
if the plane of polarization rotates from vertical in a clockwise position
then + enantiomer
racemate with plane polarised light
no overall effect on the plane of polarisation therefore they are considered optically inactive
biochem just to say
enantiomers of molecules in biological systems usually aren’t both there. only one is used and synthesised. this is because to be complementary to a receptor, the other enantiomer probably has way less compatibility if any
sugar and amino acids are chiral molecules as well as proteins and nucleic acids. crazy
their shape is important when left handedness and right handedness makes a difference: one optical isomerism will facilitate a biochemical reaction and the other won’t, or will have a different effect
chirality is important in drug action. the pharmacology of a drug is influenced by the binding affinity between it and the target, which is affected by chirality
