Chirality - Organic Chem II

Question 1

Define sterioisomer:

Answer 1

Atoms are arranged differently in space

Question 2

What is optical isomerism:

Answer 2

It occurs when a carbon atom in a molecule has 4 different groups or atoms attached to it. Forms a non superimposable mirror image isomer

Question 3

What would two enantiomers have?

Answer 3

Identical chemical and physical properties except for the way they rotate plane-polarised light.
One enantiomer would rotate plane-polarised light in a clockwise direction by a certain angle, the enantiomer would rotate plane-polarised light in the anticlockwise direction, by the same angle

Question 4

What is a racemic mixture?

Answer 4

An equimolar mixture of two enantiomers.
Racemic mixtures have no effect on plane-polarised light because the rotation of each enantiomer cancel out

Question 5

Why does the product of an SN1 mechanism not rotate plane-polarised light?

Answer 5

• The carbocation intermediate is planar
• Therefore the nucleophile can attack from either side, with equal probability
• So a 50:50 mixture of the two enantiomers is produced

Question 6

Why does the product of an SN2 mechanism rotate plane-polarised light?

Answer 6

• The nucleophile attacks from an angle opposite to the leaving group.
• As the new bond starts to form before the existing bond has properly broken, the product is only a single enantiomer