Organic II- optical isomers

Question 1

What is optical isomerism?

Answer 1

A type of stereoisomerism where molecules have the same molecular formula but a different spatial arrangement of atoms. It occurs when molecules have a single chiral centre.

Question 2

What is a chiral centre?

Answer 2

A carbon atom with four different groups bonded around it so there is no line of symmetry to the molecule.

Question 3

What are enantiomers?

Answer 3

They are optical isomers which are mirror images of each other. Each enantiomer causes the rotation of plane polarised light by 90° in opposite directions.

Question 4

What is a racemate/racemic mixture?

Answer 4

It is a mixture of equal amounts of enantiomers.

Question 5

Why is a racemate/racemic mixture optically inactive?

Answer 5

Both enantiomers have opposite directions of rotations of polarised light, meaning this cancels out in this mixture. As a result this mixture is optically inactive.

Question 6

How is a racemic mixture formed?

Answer 6

Through a nucleophilic addition reaction where nucleophiles attack a molecule with a carbonyl group from above or below the carbon-oxygen double bond. This means the two different products produced are optical isomers.