DF9: Isomerism

Question 1

Define “isomers”

Answer 1

Molecules with the same molecular formula but with different arrangement of the atoms

Question 2

What are the two types of isomerism?

Answer 2

• Structural isomerism

- Stereoisomerism

Question 3

Define “structural isomers”

Answer 3

Molecules with the same molecular formula but with the atoms bonded together in a different order

Question 4

Name the 3 types of structural isomer

Answer 4

• Chain isomerism
• Position isomerism
• Functional group isomerism

Question 5

What is chain isomerism?

Answer 5

Molecules with the same molecular formula having different arrangements of the carbon skeleton

Question 6

What are the two ways carbon skeletons can be arranged?

Answer 6

• As a straight chain

- As branched chains

Question 7

Are the chemical properties of chain isomers similar or different?

Answer 7

Similar

Question 8

Are the physical properties of chain isomers similar or different?

Answer 8

Different

Question 9

Give one physical property of chain isomers that differ and why.

Answer 9

Boiling point differs because of the changes in the shape of the molecule

Question 10

The more ____ in an alkane, the more chain isomers it has.

Answer 10

Carbon atoms

Question 11

Which alkanes have no chain isomers?

Answer 11

• CH4
• C2H6
• C3H8

Question 12

What is position isomerism?

Answer 12

Molecules with the same molecular formula having their functional group situated in different positions on the carbon chain

Question 13

Are the physical properties of position isomers similar or different?

Answer 13

Different

Question 14

Are the chemical properties of position isomers similar or different?

Answer 14

Different

Question 15

What is functional group isomerism?

Answer 15

Molecules having the same molecular formula but different functional group

Question 16

Are the physical properties of position isomers similar or different?

Answer 16

Different

Question 17

Are the chemical properties of position isomers similar or different and why?

Answer 17

Different as they belong to different homologous series

Question 18

What are the two types of stereoisomer?

Answer 18

• E/Z isomerism

- Optical isomerism

Question 19

Explain how E/Z isomers form in alkenes due to restricted rotation

Answer 19

• Alkanes don’t contain any double bonds, single bonds allow atoms to rotate freely so they cannot form isomers of each other
• Alkenes have at least one double bond, double bonds are rigid and don’t allow the atoms to rotate
• Alkenes still contain single bonds in their molecules which means atoms can rotate these

Question 20

When is an alkene an E isomer?

Answer 20

When the hydrogens are across the double bond

Question 21

When is an alkene a Z isomer?

Answer 21

When the hydrogens are on the same side of the double bond

Question 22

When do we use the terms “E or Z isomer”?

Answer 22

Only when the two groups that are the same are hydrogens

Question 23

What is an E isomer also known as?

Answer 23

Trans isomer

Question 24

What is an Z isomer also known as?

Answer 24

Cis isomer

Question 25

What is optical isomerism?

Answer 25

When two compounds are non superimposable mirror images of each other

Question 26

When does optical isomerism usually happen?

Answer 26

A central carbon atom with four groups arranged around it

Question 27

What property of alkenes allows E/Z isomers to form?

Answer 27

Restricted rotation around the C-C double bonds