3.3.7 - Optical isomerism

What are stereoisomers?

have the same structural formula but have the atoms arranged differently in space.

What are the two types of stereoisomers?

The two types of sterioisomersism is geometrical and optical.

What is a chiral carbon?

Carbon with four different atoms/groups of atoms attached to it is called a chiral carbon.

Do chiral carbons exist as optical isomers?

Compounds with a chiral centre exist as two optical isomers

What is the name of these two optical isomers?

enantiomers

What are enantiomers?

Enantimers are mirror images which are non-superimposable mirror images.

What is the similarity and difference between enantiomers?

Their physical and chemical properties are identical but they differ in their ability to rotate plane polarised light.

What directions do the enantiomers rotate?

One of the enantiomers rotate the plane polarised light clockwise, and the other does it anticlockwise.

What can the rotation be used to determine?

This rotation can be used to determine the identity of an optical isomer of a single substance.

How do you identify a chiral centre?

check whether the carbon is bonded to four different atoms/groups of atoms.

What are chiral centres marked with in 3d drawings?

In 3D drawings, chiral centres are marked with a *

What is a racemic mixture?

A racemic mixture is where there are equal amounts of enantiomers present in the solution.

What does an optically active mixture need?

If a solution has an uneven mixture of each enantiomer, the reaction mixture is optically active (e.g - 20% of the enantiomers rotate clockwise and 80% rotate anticlockwise).

Are racemic mixtures optically active or inactive?

inactive

Why are racemic mixtures optically inactive?

This is optically inactive as the enantiomers will cancel out each others effect - plane of polarised light wil not change.

What happens in the pharmaceuticals

In pharmaceutical industry, it is much easier to produce synthetic drugs that are racemic mixtures than producing enantiomer of the drug

What is separating the enantiomers called?

enantiopure.

What are the disadvantage of enantiopure?

This is a very expensive and time consuming separation process. Usually, this separation process is not worthwhile.

Why is only one enantiomer produced sometimes?

The other enantiomer could be harmful
The drug could be expensive to synthesize.