13.2 Stereoisomerism

Question 1

What are stereoisomers?

Answer 1

They have the same structural formula but different arrangement of the atoms in space

Question 2

Two types of isomerism

Answer 2

E/Z isomerism

Optical isomerism

Question 3

When does E/Z isomerism take place?

Answer 3

Occurs in compounds with a C=C double bond

Question 4

Why does stereoisomerism arise?

Answer 4

Rotation around the double bond is restricted

Groups attached to carbon atom are fixed relative to each other

Question 5

What causes the rigidity between the C=C double bond?

Answer 5

The position of the pi bond’s electron density above and below the plane of the sigma bond

Question 6

Conditions for E/Z isomerism

Answer 6

C=C double bond

Different groups attached to each carbon atom of the double bond

Question 7

Conditions for cis-trans isomers

Answer 7

C=C double bond
Each Carbon must be attached to 2 different groups
One of the groups on each Carbon atom of the double bond must be the same

Question 8

Which isomer is cis and which is trans?

Answer 8

Cis isomer is the Z isomer

Trans isomer is the E isomer

Question 9

When can the cis-trans system of naming be used?

Answer 9

When each Carbon atom in the double bond is attached to a single hydrogen atom

Question 10

Cahn-Ingold-Prelog rules

Answer 10

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

Question 11

How is priority given?

Answer 11

Look at the atoms attached to the Carbon atoms and the one with higher atomic number is higher priority

Question 12

If two atoms attached to a Carbon atom in a double bond are the same….

Answer 12

Find the first point of difference - the one with higher atomic number at this point is the higher priority group