10.5 Stereoisomerism Flashcards
What are stereoisomers?
Molecules that have the same structural formula ie. atoms that are joined together int he same way but the atoms are arranged differently in space.
What are conformational isomers?
The same molecule in different conformations due to the rotation about a sigma bond. They are both the same molecule and interconvert rapidly, individual conformers cannot be isolated. No bonds are broken when conformer interconvert.
What are configurational isomers?
Can be divided into cis-trans and optical isomers and the different isomers can only be interconverted by breaking and reforming covalent bonds.
What are the conditions for a molecule to exhibit cis trans isomerism?
There must be two different groups on both sides of the double bond.
Why does cis trans isomerism occur?
Because the pi components of the C=C prevents rotation of groups about the bond the groups cannot be rated around the bond without breaking the pi component.
How is cis trans isomerism possible for substituted cycloalkanes?
The ring structure prevents rotation of a group from the top of the ring to the bottom.
How are cis trans isomers be named using E/Z system.
Each group attached to the C=C is given a priority where the higher priority is given to atom attached to the C=C that have a higher atomic number. We look at each C in the C=C separately and assign a priority 1 or 2 to each of the group attached. If the two groups with the highest priority are on the SAME side of the C=C the isomer is labelled Z and if they are on OPPOSITE sides of the C=C the simmer is labelled E.
How must a molecule exhibit optical isomerism?
There must be four different groups attached to a C atom.
What is a carbon called with fur different atoms of groups attached to it?
Chiral centre, and molecules that exhibit optical isomerism are called chiral.
What are the individual optical isomers of a compound called?
Enantiomers they are non superimposable mirror images.
What is plane polarised light?
Light that vibrates in one plane only.
How is plane polarised light passed through the enantiomers?
In a polarimter.
What do the two enantiomers of an optically active compound do to the light?
Rotate the plane of polarisation of plane polarise light in opposite directions by equal amounts.
What is a racemic mixture?
An equimolar mixture of the two enantiomers of a chiral compound.
What effect does a racemic mixture have on plane polarised light?
No effect, optical inactive, since the rotations of the two enantiomers cancel each other out.
