B3 - Sterioisomers

Question 1

What are sterioisomers?

Answer 1

Sterioisomers have the same structural formula but a different arrangement of the atoms in space.

Question 2

What does E/Z isomerism only occur in?

Answer 2

Compounds with a C==C double bond.

Question 3

What two conditions must a molecule satisfy to have E/Z isomerism?

Answer 3

1. A C==C double bond
2. Different groups attached to each carbon atom of the double bond

Question 5

How are cis-trans isomers different to E/Z isomers?

Answer 5

In cis-trans isomers, one of the attached groups on each carbon atom of the double bond MUST be the same.

Question 6

What is the difference between the cis and trans isomer?

Answer 6

• The cis isomer has the same groups on each carbon on the same side of the molecule
• The trans isomer has the same groups on each carbon diagonally opposite each other

Question 7

How can you match up E/Z isomers with cis-trans isomers when there is a hydrogen on each of the double-bonded carbon atoms?

Answer 7

• The cis isomer is the Z isomer
• The trans isomer is the E isomer

Question 8

How can you use the Cahn-Ingold Prelog rules?

Answer 8

• If the groups of higher priority are on the same side of the double bond, the compound is the Z isomer
• If the groups of higher priority are diagonally placed across the double bond, the compound is the E isomer

Question 9

What are the two steps to assigning priority to groups?

Answer 9

• The higher the atomic number, the higher the priority - examine the atoms attached directly to the carbon atoms of the double bond
• If the two atoms attached to a carbon atom in the double bond are the same, then you will need to find the first point of difference. The group which has the higher atomic number at the first point of difference is given the higher priority