13.2 Steroisomerism

Question 1

What are the two typos of stereoisomerism?

Answer 1

E/Z isomerism, optical isomerism

Question 2

Definition of stereoisomers

Answer 2

Compounds with the same structural formula but a different arrangement of atoms in space

Question 3

In what compounds does E/Z isomerism and optical isomerism occur in?

Answer 3

E/Z isomerism - only occur in compounds with a C=C bond

Optical isomerism - occur in much wider range of compounds, including alkenes with no functional groups

Question 4

Why does stereoisomerism occur around double bonds?

Answer 4

The double bond is restrictive and non-rotational, the groups attached to the carbon are fixed relative to each other. This is due to π bonds electron density above and below the plane of the σ bond

Question 5

What are the conditions required for E/Z isomerism?

Answer 5

-C=C double bond
-Different groups attached to each C of the double bond

Question 6

Why does but-1-ene not show E/Z isomerism but but-2-ene does?

Answer 6

-The first carbon in but-1-ene has 2 hydrogen atoms attached to it
-But-2-ene has a methyl group and a hydrogen atom on each C of the double bond

Question 7

What is cis-trans isomerism?

Answer 7

-special case of E/Z isomerism
-same as E/Z isomers there is a C=C bond and 2 different groups attached to each carbon
-have the same attached group on each atom of the double bond

Question 8

Which isomer of but-2-ene is cis and which is trans and why?

Answer 8

-cis isomer is the Z isomer, the hydrogen atoms and methyl groups on each carbon in the double bond is on the same side of the molecule
-trans isomer is the E isomer, the hydrogen and methyl groups are diagonally opposite each other

Question 9

Which E/Z isomer is the trans isomer

Answer 9

E isomer

Question 10

Which E/Z isomer is the cis isomer

Answer 10

Z isomer

Question 11

When can cis-trans isomerism only be used?

Answer 11

When the substituent groups on each carbon atom in the double bond is the same

Question 12

What does the Cahn-Ingold-Prelog nomenclature tell us?

Answer 12

-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 13

What are the steps of the Cahn-Ingold-Prelog nomenclature?

Answer 13

Step 1 - Assigning priority
Determine the atomic number of the atoms attracted to the carbon atoms of the double bond, the higher the atomic number, the higher the priority
Step 2 -
If the groups attached to the C atom in the C=C bond are the same, then you should find the first point of difference that is given and the group with the higher atomic number at the first point of difference is given the priority