3.3.7 Optical Isomerism

Question 1

What is optical isomerism?

Answer 1

A type of stereoisomerism where isomers have the same structural formula but different arrangement of atoms in space.

Question 2

What does optical isomerism result in?

Answer 2

Two non-superimposable mirror images called enatiomers.

Question 3

What is a chiral carbon (or stereocentre)?

Answer 3

A carbon atom bonded to four different groups.
This allows the formation of two enantiomers

Question 4

Which carbon in 2-chlorobutane is chiral and why?

Answer 4

The second carbon is chiral because it’s bonded to a Cl, a CH₃, a CH₂CH₃, and a H - all different groups.

Question 5

How can you identify and draw optical isomers?

Answer 5

• Identify the chiral centre - look for a carbon with 4 different groups.
• Draw one enantiomer with a tetrahedral layout.
• Sketch the mirror image - the second enantiomer with a dotted line to show miror.

Question 6

What happens when a molecule has more than one chiral carbon?

Answer 6

The number of optical isomers increases.

Question 7

What does it mean for a molecule to be optically active?

Answer 7

It means the molecule can rotate plane-polarised light
One enantiomer rotates it clockwise, the other anticlockwise by the same angle.

Question 8

What is a racemic mixture (racemate)?

Answer 8

An equimolar, 1:1, mixture containing equal amounts of two enatiomers
Racemate exhibit no optical activity as opposing rotations cancel out.

Question 9

Why is optical isomerism important in medicine?

Answer 9

Enantiomers can have different effects in the body.
One may be therapeutic, while the other may be inactive or harmful.
It is why separating enantiomers in drugs is crucial.