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A Level Organic Chemistry > 3.4 Alkenes > Flashcards

3.4 Alkenes Flashcards

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1
Q

What is an alkene?

A

Unsaturated hydrocarbon with C=C double bond

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2
Q

What is the general formula of an alkene?

A

CnH2n

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3
Q

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

A

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

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4
Q

Are they more or less reactive than alkanes.
Why?

A

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

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5
Q

What intermolecular forces of attraction do they have.

A

Only VDW due to non-polar bonds

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6
Q

Are they soluble in water? Why?

A

No, non-polar bonds (VDW < Hydrogen bonding)

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7
Q

Name and describe the three kinds of isomers alkenes can have

A

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

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8
Q

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

A

CH3CH=CHCH2CH3 + 7 1/2O2 —> 5CO2 + 5H2O

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9
Q

What is an electrophile?

A

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

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10
Q

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

A

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

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11
Q

Major products will be formed from which kinds of carbocations?

A

Tertiary (or the most stable available)

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12
Q

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

A

Acid catalyst, usually phosphoric acid

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13
Q

What are the product(s) of the reaction?

A

An alcohol

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14
Q

Draw a mechanism for the addition of water to ethene

A

Slide 30

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15
Q

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

A

Room temperature

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16
Q

Draw a mechanism for the reaction of HBr and ethene?

A

Slide 34

17
Q

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

A

Room temperature and organic solvent

18
Q

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

A

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

19
Q

Draw a mechanism for the reaction between bromine and ethene

A

Slide 40

20
Q

Draw a mechanism for the reaction of sulfuric acid with ethene

A

Slide 41

21
Q

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

A

Add water

H2SO4 reforms showing it catalyses the hydration of alkenes

22
Q

What is an addition polymer?

A

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

23
Q

What are monomers? What form do they usually take?

A

Molecules which combine to form a polymer

Usually have a C=C bond which breaks to leave a repeating pattern

24
Q

Draw how you would represent the polymerisation of ethene

A

Slide 50

25
Q

Give 3 uses of poly(chloroethene) / PVC

A

Drainpipes

Vinyl

Aprons

26
Q

Give to examples of plasticisers

A

Esters and phthalates

27
Q

What are plasticisers?

A

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

28
Q

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

A

PVC with plasticiser become flexible, used for aprons

Without a plasticiser, PVC is rigid, used for drainpipes

29
Q

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

A

Bonds are non-polar so are not attacked by enzymes

30
Q

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

A

Disposal is very problematic

31
Q

What is mechanical recycling

A

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

32
Q

What is mechanical recycling used for?

A

Soft drink bottles —> fleeces

33
Q

What is feedstock recycling?

A

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

34
Q

What is feedstock recycling used for?

A

Making totally new plastics

35
Q

What is a problem with recycling?

A

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

A Level Organic Chemistry (16 decks)

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