13.2 - Stereoisomerism

Question 1

What is stereoisomerism ?

Answer 1

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

Question 2

Define alkanes

Answer 2

Unsaturated hydrocarbons with at least 1 double covalent bond

Question 3

What is the general formula of alkanes ?

Answer 3

CH2n

Question 4

Why are alkanes fairly reactive ?

Answer 4

Due to their high electron density

Question 5

When do you use E/Z isomerism ?

Answer 5

When you have 2 different atoms / or group of atoms on the same carbon

Question 6

What is E/Z isomerism ?

Answer 6

stereoisomerism around double bonds arises because rotation about the double bond is restricted and the groups attached to each carbon are therefore fixed relative to each other

Question 7

What is the reason behind the rigidity of E/Isomerism ?

Answer 7

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

Question 8

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

Answer 8

• a C=C double bond
• different groups attached to each carbon atom of the double bond

Question 9

Explain why but-1-ene is not E/Z isomerism but but-2-ene is ?

Answer 9

• draw out but-1-ene and but-2-ene *
• in but-1-ene on the left hand side the carbon is attached to 2 hydrogen atoms so this structure does not satisfy the second condition
• in but-2-ene on the left hand side the carbon is attached to a methyl group and one hydrogen atom thus satisfying the 2nd condition

Question 10

What is cis isomerism ?

Answer 10

• taking the last flash card as a example *
• the hydrogen and methyl on each carbon in the double bond are on the same side of the molecule
• non hydrogen groups/atoms on the same side of the C=C bond

Question 11

What is cis isomerism E or Z ?

Answer 11

Z

Question 12

What is trans isomerism ?

Answer 12

• The H atom and methyl group are diagonally opposite each other
• non hydrogen groups/atoms on opposite sides of the C=C bond

Question 13

Is trans isomerism represented as E or Z ?

Answer 13

E

Question 14

When can cis-trans be used ?

Answer 14

Can on,y be used when each carbon atom in the double bond is attached to a single H atom

Question 15

What does the CIP rule state ?

Answer 15

In this system atoms attached to each carbon atom in a double bind are given priority based upon their atomic number

• if the group that is higher priority are on the same side of the double bond = compound is the Z isomer
• if the groups are higher priority are diagonally placed across the double bond = compound is a E isomer

Question 16

What happens if 2 atoms are attached to a carbon atom in the double bond are the same ?

Answer 16

• find the first point of difference
• group with a higher atomic number at the first point f difference is higher priority