Nomenclature and isomerism

Question 1

What is optical isomerism

Answer 1

Optical isomerism is a form of stereoisomerism and occurs as a result of chirality in molecules.

Question 2

When are molecules optical isomers

Answer 2

Molecules are optical isomers when they are non-superimposable mirror images of one another (chiral).

Question 3

What is the chiral centre

Answer 3

The carbon bonded to the four different groups or the asymmetric carbon atom.

Question 4

What is polarised light

Answer 4

When waves of light are limited to one plane

Question 5

Define an enantiomer

Answer 5

When two isomers are chiral they are said to be a pair of enantiomers

Question 6

What is a racemic mixture/ racemate

Answer 6

A mixture of equal amounts of enantiomers

Question 7

What is the problem faced by the drug industry posed by optical isomerism

Answer 7

As most drugs rely on the shape of the molecule to work, only one of a pair of enantiomers will be effective

Question 8

Name 3 options drug industry uses when dealing with enantiomers

Answer 8

• separate the two isomers- very difficult and expensive as optical isomers have very similar properties
• sell the mixture as a drug- wasteful as half is inactive
• design an alternative synthesis of the drug that makes only the required isomer

Question 9

What is the effect of enantiomers on polarised light

Answer 9

One enantiomer will rotate the polar light clockwise (+)

The other will rotate the polar light anticlockwise (-)

Question 10

What is optical activity

Answer 10

If a molecule is capable of optical rotation it is said to be optically active. All chiral molecules are optically active

Question 11

What does a racemate do to polarised light

Answer 11

Nothing. It is said to be optically inactive as the enantiomers rotate light in opposite but equal directions meaning there is no overall effect