Alkenes - Organic 1

Question 1

What is an alkene?

Answer 1

Unsaturated hydrocarbons with a C=C double bond

Question 2

What is the general formula of an alkene?

Answer 2

CnH2n

Question 3

Why is there no rotation about the C=C double bond?

Answer 3

Due to the π (pi) orbital - electron density above and below the single bond, which holds the carbon atoms in place

Question 4

Are they more or less reactive than alkanes? Why?

Answer 4

More reactive, due to high electron density of double bond and the fact the pi-bond is slightly easier to break

Question 4

What intermolecular forces of attraction do they have?

Answer 4

Only van der Waals due to non-polar bonds

Question 5

Are they soluble in water? Why?

Answer 5

No, non-polar bonds (van der Waals’ < hydrogen bonding)

Question 6

Name and describe the
three kinds of isomers
alkenes can have

Answer 6

Chain isomers (branched chains)
Position isomers (C=C on different carbon atom)
Geometric E-Z isomers (Z is when 2 highest atomic number chains are on the same side of the double bond; E is when they’re on opposite sides)

Question 7

Write an equation for the complete combustion of pent-2-ene.

Answer 7

CH3CH=CHCH2CH3 + 71⁄2O2 → 5CO2 + 5H2O

Question 8

What is an electrophile?

Answer 8

Electron deficient atoms/ions which accept a pair of electrons (here, from the C=C double bond)

Question 9

What is the most stable type of carbocation intermediate? why?

how do you determine whether a major or minor product is formed from an addition reaction?

Answer 9

Alkyl groups have a positive inductive effect, so the most stable carbonation is the one bonded to the most other carbon atoms i.e. A tertiary carbocation

the initial place where the other thing is added e.g. bromine to a carbocatio, then talk about above stuff in a long worded response.

Question 10

Major products will be formed from which kinds of carbocations?

Answer 10

Tertiary (or the most stable avaliable)

Question 11

What conditions are needed for the electrophilic addition of H2O to an alkene?

Answer 11

Acid catalyst, usually phosphoric acid

Question 12

What are the product(s) of the reaction?

Answer 12

An alcohol

Question 13

Draw a mechanism for the addition of water to ethene

Answer 13

check google

Question 13

What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?

Answer 13

Room temperature

Question 14

How does a molecule with a non-polar bond react as if it is an electrophile?

Answer 14

C=C double bond with a high electron density induces a temporary dipole in the halogen molecule → δ+ atom attracted to double bond

Question 14

Draw a mechanism for the reaction of HBr and ethene.

Answer 14

check google

Question 15

What conditions are needed for the electrophilic addition of a halogen molecule to an alkene?

Answer 15

Room temperature and organic solvent

Question 16

How would you turn the product (from sulfuric acid + ethene) into an alcohol and how does this show that sulfuric acid catalyses the addition of water to an alkene?

Answer 16

Add water
H2SO4 reforms, showing it catalyses the hydration of alkenes

Question 16

Draw a mechanism for the reaction between bromine and ethene

Answer 16

check google

Question 17

Draw a mechanism for the reaction of sulfuric acid with ethene.

Answer 17

check google

Question 18

What is an addition polymer?

Answer 18

many monomers bonded together via rearrangement of bonds without the loss of any atom or molecule

Question 19

What are monomers? What form do they usually take?

Answer 19

Molecules which combine to form a polymer Usually have a C=C bond which breaks to leave a repeating pattern

Question 20

Draw how you would represent the polymerisation of ethene.

Answer 20

check google

Question 21

Give 3 uses of poly(chloroethene) / PVC

Answer 21

Drainpipes Vinyl Aprons

Question 22

Give two examples of plasticisers

Answer 22

esters and phthalates

Question 23

What are plasticisers?

Answer 23

Small molecules that get between polymer chains to force them apart and allow them to slide over one another

Question 24

How do the physical properties of PVC change due to a plasticiser? What applications
does this lead to?

Answer 24

PVC with a plasticiser become flexible, used for aprons
Without a plasticiser, PVC is rigid, used for drainpipes

Question 25

Why do things containing mainly C-C and C-H bonds not decompose easily?

Answer 25

Bonds are non-polar so are not attacked by enzymes

Question 26

Why is a lack of biodegradability in compounds with C-C or C-H bonds a problem?

Answer 26

Disposal is very problematic

Question 27

What is mechanical recycling?

Answer 27

Where plastics are separated into different types, washed, ground down, melted and re-moulded

Question 28

What is mechanical recycling used for?

Answer 28

Soft drinks bottles → fleeces

Question 29

What is feedstock recycling?

Answer 29

Plastics heated to a temperature which break polymer bonds, leaving original monomers that can be made into new plastics

Question 30

What is feedstock recycling used for?

Answer 30

Making totally new plastics

Question 31

What is a problem with recycling?

Answer 31

Each time thermosoftening plastics are melted and remoulded, their properties degrade, so they can only be remoulded a limited number of times

Question 32

info. about electrophilic addition:

Answer 32

breaks double bond, adds more in, major/minor products formed

uses HBr/ Br2 / H2SO4

Question 33

info. about addition polymers

Answer 33

high pressures and temps. = branched opposite = straight with strong imfs

Question 34

which way do curly arrows go?

Answer 34

negative to positive