Compounds with multiple chiral centres

From the 3rd lecture of Sterochemistry

How can we calculate the maximum number of stereoisomers in a compound with multiple chiral centres

-We do so by considering each possible configuration of R and S for each of the molecules.

-We can do so mathematically by labelling n as the number of chiral centres, then doing 2^n = no. stereoisomers.

What happens when the chiral centres are the same

If chiral centres are the same this gives rise too the possibility of forming a meso-isomer, where it will be identical when mirrored giving it a superimposable mirror image.

How does a compound having multiple identical chiral centres effect the number of Stereoisomers that form.

Use example of a 2 centred chiral compound.

Forms a meso-isomer

As two of the possible molecules formed are identical it will form less stereoisomers then the 2^n equation would suggest.

Also leads to less enantiomers forming as well as less Diastereoisomers.

Instead of forming 4 stereoisomers it will for 3 as A=B, this also means it will only form 1 pair of enantiomers rather then 2 as the A,B enantiomer are superimposable. Will also only form 3 diastereoisomers instead of 4.

Describe what is a Diastereoisomer

They are stereoisomers that are not enantiomers, as they are not mirror images.

They all have different physical properties

They are easily separable and react differently

Not necessarily optically active as they could be meso-isomers