13. Alkenes

Question 1

What is the functional group of alkenes?

Answer 1

CnH2n

Question 2

Is alkene saturated or unsaturated?

Answer 2

Unsaturated

Question 3

Why is alkene unsaturated?

Answer 3

Because it contains a double bond/pi bond.

Question 4

Is alkene reactive?

Answer 4

Yes, because it contains the double bond which contains a pi bond. It is weaker than sigma bonds so that single bonds, so it is easier to break.

Question 5

What are stereoisomers/geometric isomers?

Answer 5

Isomers that have the same structural formula but different arrangement in space.

Question 6

How can E/Z isomerism occur?

Answer 6

1. there is a C=C double bond
2. each carbon is bonded to a different atom/group

Question 7

How does the C=C double bond cause E/Z isomerism to occur?

Answer 7

The pi bond in alkenes restricts the rotation of molecules.

Question 8

How does E(entgegen)/Trans isomer look like?

Answer 8

Atoms/groups on the opposite sides.

Question 9

How does Z(zusammen)/Cis isomer look like?

Answer 9

Atoms/groups on the same sides.

Question 10

How is cis-trans isomer different from E/Z isomer?

Answer 10

In cis-trans isomers, one of the attached group on each carbon atom must be hydrogen.

Question 11

What does CIP(Cahn, Ingold & Prelog) Rule do?

Answer 11

To assign isomers stereoisomers when the groups are not identical

Question 12

How to use the CIP(Cahn, Ingold & Prelog) Rule to identify E/Z isomers?

Answer 12

1. use the atomic number of the atom that is directly bonded to the C=C bond
2. if the atomic number is equal, the next atom is taken into account
3. identify if it is E or Z isomer
   ☆ halogens are heavier in 99% of situations ☆

Question 13

Alkene + halogen > ?

Answer 13

Dihalogenoalkane

Question 14

Alkene + hydrogen halide > ?

Answer 14

Halogenoalkane

Question 15

Alkene + water (with acid catalyst) > ?

Answer 15

Alcohol

Question 16

Alkene + hydrogen > ?

Answer 16

Alkane

Question 17

What happens during electrophile addition reaction?

Answer 17

1. an electron from the hydrogen is taken from the halogen, the bond is broken by heterolytic fission
2. hydrogen becomes delta positive and halogen becomes delta negative
3. one of the bond from the double bond from the alkene is moved to the hydrogen
4. hydrogen is joined to the alkene
5. a carbocation is formed and the carbon from the alkene that lost a bond becomes positively charged
6. a negatively charged halogen is joined to the carbocation (alkene)

Question 18

What is heterolytic fission?

Answer 18

The breaking of covalent bond forming a cation (positive ion) and anion (negative ion).

Question 19

What is a carbocation?

Answer 19

An ion that contains a positively charged carbon atom.

Question 20

What is Markownikoff’s Rule?

Answer 20

Methyl carbocation is the least stable, then primary, then secondary, and tertiary carbocation is the most stable.

Question 21

How does the number of alkyl affect the stability of carbocations?

Answer 21

The more alkyl groups attached to the positively-charged atom > the more the charge is spread out > ion is more stable

Question 22

What is addition polymerisation?

Answer 22

Formation of a very long molecular chain by repeated addition reactions of many unsaturated alkene molecules.

Question 23

Will the polymer be saturated or unsaturated after addition polymerisation?

Answer 23

Saturated

Question 24

What are the benefits for sustainability of processing waste polymers by?

Answer 24

1. combustion for energy production
2. use as an organic feedstock for the production of plastics and other organic chemicals
3. removal of toxic waste products eg HCl

Question 25

What are the benefits to the environment of development
of biodegradable (可生物降解) and photodegradable (可光降解) polymers?

Answer 25

1. these polymers are usually made from starch and cellulose, which microorganisms can break them down into water, carbon dioxide and biological compounds
2. these polymers contain bonds that are weakened by absorbing light to start the degradation (降解)