Alkenes

Question 1

Why does the bonding in alkenes cause stereoisomerism

Answer 1

pi bond due to overlap of orbitals above and below the plane of the molecule
leads to restricted rotation around the C=C bond

Question 2

What is stereoisomerism

Answer 2

when two double bonded carbon atoms have two different groups attatched to them
- consequence of restricted rotation around the C=C bond

Question 3

What is E/Z isomerism

Answer 3

Z isomers have groups on the same side of the double bond
E isomers have groups on opposite sides of the double bond

Question 4

How do you describe isomers as E/Z when they are comprised of four different groups

Answer 4

look at the atomic numbers of the first atom attatched to the carbon in all branches
the higher atomic number receives priority

Question 5

What is an addition reaction

Answer 5

adding two smaller molecules together to make one larger one

Question 6

What is the reagent in a hydrogenation / reduction reaction

Answer 6

H2 (g)

Question 7

What are the conditions for hydrogenation / reduction

Answer 7

150*C
nickel catalyst

Question 8

What is the product of hydrogenation / reduction

Answer 8

an alkane

Question 9

What is the reagent in halogenation

Answer 9

Br2 (l) or Cl2(g)

Question 10

What are the conditions for halogenation

Answer 10

room temperature

Question 11

What is the product of a halogenation reaction

Answer 11

a dihaloalkane

Question 12

Why is a halogenation reaction with bromine useful

Answer 12

can be used to test for the presence of a double bond

Question 13

What is the colour change for a reaction between alkenes and bromine water

Answer 13

orange -> colourless

Question 14

What are the reagents in a reaction with hydrogen halides

Answer 14

HBr, HCl, HI

Question 15

What are the conditions of a reaction with a hydrogen halide

Answer 15

room temperature

Question 16

What is the product in a reaction with a halogen halide

Answer 16

a haloalkane

Question 17

What is the reagent in a hydration reaction

Answer 17

H2o (g) - steam

Question 18

What are the conditions in a hydration reaction

Answer 18

300* - 600* C
acid catalyst ( concentrated H3PO4 )
70 atm

Question 19

What is the product in a hydration reaction

Answer 19

an alcohol

Question 20

What is the reagent in an oxidation-addition reaction

Answer 20

KMnO4 / H+ (aq)
- oxidising agent - source of O atoms

Question 21

What are the conditions for an oxidation-addition reaction

Answer 21

acid catalyst ( concentrated H3PO4 )
room temperature

Question 22

How would you test for alkenes using potassium manganate (VII)

Answer 22

add KMnO4 to excess alkene
- the purple colour of the potassium manganate disappears

Question 23

What mechanism occurs between alkenes and halogens / hydrogen halides

Answer 23

electrophilic addition

Question 24

Why are electrophiles prone to attack alkenes

Answer 24

they are attracted to the electron density of the pi bond which lies above and below the plane of the molecule

Question 25

What is an electrophile

Answer 25

a species which is attracted to negative region of charge - something with positive or delta positive charge

Question 26

Draw the electrophilic addition mechanism for the addition of HBr

Answer 26

produces a bromoalkane

Question 27

Draw the electrophilic addition mechanism for the addition of Br2

Answer 27

produces a dibromoalkane

Question 28

Draw the electrophilic addition mechanism for the addition of water

Answer 28

produces an alcohol and a H+

Question 29

What is the use of Markovnikov's rule

Answer 29

predicts the major and minor products in an addition reaction with unsymmetrical alkenes

Question 30

What does Markovnikov's rule state

Answer 30

When a hydrogen halide is added to an unsymmetrical alkene, the hydrogen adds to the carbon with the most hydrogens bonded to it already

Question 31

Why does Markovnikov's rule happen

Answer 31

due to the hydrogen adding to an end carbon, this means the carbocation is more stable as it is bonded to more carbons - label primary, secondary etc

Question 32

Why are tertiary carbocations the most stable

Answer 32

the 3 carbons around the carbocation are electron releasing the sigma bonds joining each of these to the carbocation will be polarised and draw electron density towards the carbocation - has a stabilising effect

Question 33

Give three uses for waste polymers being separated into specific types of polymer

Answer 33

1) recycling 2) incineration to release energy 3) use as a feedstock for cracking

Question 34

Give two ways how chemists limit the problems caused by polymer disposal

Answer 34

1) developing biodegradable polymers 2) removing toxic waste gases caused by incineration of plastics