13.2 Steroisomerism

Question 1

What are two types of stereoisomerism

Answer 1

E/Z isomerism

Optical isomerism

Question 2

When can E/Z isomerism occur

Answer 2

Only in compounds with a C=C double bond

Question 3

When can optical isomerism occur

Answer 3

In a wider range of compounds including alkanes with no functional groups

Question 4

When does Stereoisomerism around double bonds arise

Answer 4

Because rotation about the double bond is restricted and the groups attached to each carbon atom are therefore fixed relative to each other
The rigidity is caused by the position of the π-bond’s electron density above and below the plane of the σ-bond

Question 5

What are the conditions a molecule must satisfy in order to have E/Z isomerism

Answer 5

A C=C double bond

Different groups attached to each carbon atom of the double bond

Question 6

Which of but-1-ene and but-2-ene can have E/Z isomers

Answer 6

but-2-ene

Because it has a methyl group AND a hydrogen atom on each of the carbon atoms of the double bond

Question 7

What is Cis-trans isomerism

Answer 7

The name commonly used to describe a special case of E/Z isomerism
One of the attached groups on each carbon atom of double bond must be hydrogen

Question 8

Difference between a cis isomer and a trans isomer

Answer 8

Cis - hydrogen atoms on each carbon in double bond on SAME side of the molecule
Trans - hydrogen atoms are diagonally OPPOSITE each other

Question 9

In cis-trans isomerism

Answer 9

The cis isomer is the Z isomer

The trans isomer is the E isomer

Question 10

What are the Cahn-Ingold-Prelog rules of isomerism

Answer 10

Atoms attached to each carbon atom in double bond are given priority based upon their atomic number
If groups of higher priority on same side of double bond, compound is Z isomer
If groups of higher priority are diagonally placed across double bond, compound is E isomer

Question 11

How does priority change as atomic number increases

Answer 11

Higher number, higher priority