C. 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

molecules that have the same molecular formula, but different arrangements of atoms in space
- result of restricted rotation around the C=C bond in alkenes

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 traditional product of hydrogenation

Answer 9

used to make margarines by varying levels of hydrogenation to vary texture
- high temps caused molecules to rotate and form trans-fats

Question 10

What is the reagent in halogenation

Answer 10

Br2 (l) or Cl2(g)

Question 11

What are the conditions for halogenation

Answer 11

room temperature

Question 12

What is the product of a halogenation reaction

Answer 12

a dihaloalkane

Question 13

Why is a halogenation reaction with bromine useful

Answer 13

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

Question 14

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

Answer 14

orange -> colourless

Question 15

What are the reagents in a reaction with hydrogen halides

Answer 15

HBr, HCl, HI

Question 16

What are the conditions of a reaction with a hydrogen halide

Answer 16

room temperature

Question 17

What is the product in a reaction with a hydrogen halide

Answer 17

a haloalkane

Question 18

What is the reagent in a hydration reaction

Answer 18

H2o (g) - steam

Question 19

What are the conditions in a hydration reaction

Answer 19

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

Question 20

What is the product in a hydration reaction

Answer 20

an alcohol

Question 21

What is the reagent in an oxidation-addition reaction

Answer 21

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

Question 22

What are the conditions for an oxidation-addition reaction

Answer 22

acid catalyst ( concentrated H3PO4 )
room temperature

Question 23

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

Answer 23

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

Question 24

What mechanism occurs between alkenes and halogens / hydrogen halides

Answer 24

electrophilic addition

Question 25

Why are electrophiles prone to attack alkenes

Answer 25

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

Question 26

What is an electrophile

Answer 26

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

Question 27

Draw the electrophilic addition mechanism for the addition of HBr

Answer 27

produces a bromoalkane

Question 28

Draw the electrophilic addition mechanism for the addition of Br2

Answer 28

produces a dibromoalkane

Question 29

Draw the electrophilic addition mechanism for the addition of water

Answer 29

produces an alcohol and a H+

Question 30

What is the use of Markovnikov's rule

Answer 30

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

Question 31

What does Markovnikov's rule state

Answer 31

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 32

Why does Markovnikov's rule happen

Answer 32

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 33

Why are tertiary carbocations the most stable

Answer 33

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 34

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

Answer 34

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

Question 35

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

Answer 35

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