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Chemistry (Organic) > Alkenes > Flashcards

Alkenes Flashcards

1
Q

What is an alkene

A

An unsaturated hydrocarbon

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2
Q

What is the general formula for alkenes

A

CₙH₂ₙ

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3
Q

What mechanism can alkenes undergo when they react with an electrophile

A

Electrophilic addition

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4
Q

Why are alkenes attacked by electrophiles

A

They contain a double bond with a high electron density

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5
Q

What is an electrophile

A

An electron pair acceptor
They are deficient in electrons and are therefore attracted to the double bond in alkenes

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6
Q

Give two categories which can be electrophiles

A

Positively charged ions
Polar molecules

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7
Q

What is the test for alkenes

A

When we add bromine water, if alkenes are present, a colour change will occur from brown/orange to colourless

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8
Q

What do we form when we add bromine to an alkene

A

A dibromoalkane

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9
Q

By what mechanism does bromine react with an alkene

A

Electrophilic addition

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10
Q

Draw the mechanism for the reaction between bromine and ethene

A
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11
Q

Explain how Br2 is polar when reacting with an alkene

A

When a bromine molecule approaches the double bond in an alkene, the electrons in the nearest Br atom repel the high electron density in the double bond, causing a temporary induced dipole, and the nearest bromine atom to be be delta positive, and the bromine molecule to be polar

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12
Q

What is the intermediate called which is formed when bromine reacts with an alkene

A

A carbocation

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13
Q

What colour are dibromoalkanes

A

Colourless

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14
Q

What is formed when an alkene reacts with a hydrogen halide

A

Halogenoalkanes

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15
Q

Draw the mechanism for the reaction between hydrogen bromide and ethene

A
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16
Q

How many products do we form when a hydrogen halide reacts with an unsymmetrical alkene

A

2

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17
Q

What is the amount of a specific product that is produced dependent on when an unsymmetrical alkene reacts with a hydrogen halide

A

The stability of the carbocation intermediate

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18
Q

What determines the stability of a carbocation and explain why this is the case

A

The number of alkyl groups bonded to the carbocation
The more alkyl groups bonded, the more stable the carbocation is

This is because alkyl groups push electrons towards the positive carbocation, stabilising it

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19
Q

What is a primary, secondary and tertiary carbocation

A

Primary - 1 alkyl group bonded to the carbocation
Secondary - 2 alkyl groups bonded to the carbocation
Tertiary - 3 alkyl groups bonded to the carbocation

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20
Q

What do we call the product formed from a less stable carbocation when an unsymmetrical alkene reacts with a hydrogen halide

A

Minor product

21
Q

What do we call the product formed from a more stable carbocation when an unsymmetrical alkene reacts with a hydrogen halide

A

Major product

22
Q

Draw the mechanism for the reaction between prop-1-ene and hydrogen bromide. Identify which is the major product

A
23
Q

What are the conditions for the reaction of bromine with an alkene

A

Room temperature (not in UV light)

24
Q

What are the conditions for the reaction of hydrogen halides with an alkene

A

Room temperature

25
Q

Draw the structure of sulfuric acid

A
26
Q

What is the role of sulfuric acid when reacting with an alkene

A

Used as a catalyst in making alcohol from an alkene

27
Q

What do we form when we react sulfuric acid with an alkene

A

Alkyl hydrogen sulfate intermediates
And alcohol as product

28
Q

What are the conditions for the reaction between an alkene and sulfuric acid

A

Cold, concentrated sulfuric acid

29
Q

Draw the mechanism for the reaction between ethene and sulfuric acid to produce an alcohol, stating the intermediate formed

A
30
Q

What can we add to an alkyl hydrogen sulfate to reform sulfuric acid, what is this process called

A

Cold water
Hydrolysis

31
Q

Write the equation for the two steps in forming an alcohol from ethene on addition of cold, concentrated sulfuric acid

A
32
Q

What are the conditions required for the hydrolysis of an alkyl hydrogen sulfate

A

Add cold water to warm a warm alkyl hydrogen sulfate

33
Q

How are polymers made from alkenes

A

Alkenes are monomers which can join together to form addition polymers

34
Q

What are the 2 types of polymers

A

Natural (Proteins & natural rubber)
Synthetic (e.g. Polypropene)

35
Q

Give an example of how polymers have developed over time

A

Charles Goodyear in 1844 discovered vulcanised rubber which is now still used in car tyres (goodyear tyres)
In the last 100 years polymers such as nylon and Teflon have improved our standard of living
New polymers continue to be synthesised to this day

36
Q

Draw the polymer of propene

A

Don’t put the n in the corner when showing a specific number of repeating units

37
Q

Why are poly(alkenes) normally unreactive and what effect can this have on the environment

A

Poly(alkenes) are saturated molecules which are normally non polar meaning they are unreactive. Thus, they don’t degrade well in landfill

38
Q

What affects the properties of a polymer

A

Intermolecular forces

39
Q

What type of attraction is present between poly(alkenes)

A

Most poly(alkene) chains are non polar so they only have van der waals forces between the chains

40
Q

What affects the strength of the van der waals forces between poly(alkene) chains

A

The longer the chain and the closer they are to each other, the more VDW forces there are (and the stronger they are)

41
Q

Give 2 properties of flexible and weak polymers

A

Shorter chain length
A lot of branching

42
Q

Why does branching affect the strength of a polymer

A

The more branches there are, the less close the polymer chains can be packed next to each other, meaning less and weaker VDW forces

43
Q

Give 2 properties of strong and rigid polymers

A

Long chain length
Little or no branching

44
Q

Explain why polyalkenes with halogens bonded to them have different properties to than those without

A

They are polar, and so they can form permanent dipole-dipole forces which are stronger than VDW forces. Thus, they will have different properties to other non polar polyalkenes

45
Q

Give an example of a polyalkene with halogen bonded to it, and give one use of it

A

PVC (polyvinyl chloride)
Drain pipes (strong polymer so weather resistant)

46
Q

What is the role of plasticisers

A

Plasticisers make polymers more flexible

47
Q

Explain how plasticisers make a polymer more flexible

A

_ Plasticisers slide between the polymer chains, pushing them apart
- This weakens the IMF between the chains
- The chains can now slide over each other more, which makes the polymer easier to bend

48
Q

State how the properties of PVC change when it is modified using a plasticiser.
Give an example of a use of PVC with and without modification using a plasticiser

A

PVC is hard and brittle which can be used in drain pipes
PVC with plasticiser added to it is more flexible which can be used for electrical cable insulation and clothing

49
Q

Give an example of a use of PVC with modification using a plasticiser

A

Electrical cable insulation and clothing

Chemistry (Organic) (8 decks)

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