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CHEMISTRY (AS) > Alkenes > Flashcards

Alkenes Flashcards

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1
Q

What are Alkenes?

A

⦾ Unsaturated HCs
⦾ (+)1 C=C - area of high e- density
⦾ Reactive due to C=C
⦾ CnH2n

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2
Q

How can you identify Alkenes?

A

⦾ Shake Alkene with orange bromine water

⦾ Turns solution orange-brown to colourless (+ve test_

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3
Q

What are electrophiles?

A

⦾ Electron acceptors
⦾ Electron defficient
⦾ Attracted to areas of high e- density
⦾ +vely charged

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4
Q

Give 3 examples of electrophiles?

A

⦾ HBr
⦾ Br2
⦾ H2SO4

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5
Q

What generally happens in an electrophillic addition reaction?
e.g. CH2CH2 + X-Y → CH2XCH2Y

A

1 ⦾ C=C repels e-s in X-Y
2 ⦾ Polaries bond in X-Y
3 ⦾ 2 e- from C=C attack 𝛿+ X creating new bond between C-1 and X
4 ⦾ X-Y bond breaks and e-s from bond taken by Y to form -ve ion with lone e- pair
5 ⦾ C-2 left with +ve charge (bond with C=C that broke took e-s to form bond with X) - carbocation intermediate
6 ⦾ :Y- acts as nucleophile
7 ⦾ It attacks +ve carbocation, donating its lone e- pair + forming bond with C-2
8 ⦾ Overall, X-Y has been added to alkene across C=C to form saturated compound.

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6
Q

What happens if you draw the mechanism involving an unsymmetrical alkene?

A

⦾ 2 different carbocation form

⦾ More stable carbocation more likely to form (make sure to draw right one)

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7
Q

What is the product for the electrophilic addition reaction for:
Heat: Ethene + Water + conc. sulfuric acid

A

⦾ Ethanol

⦾ Overall: CH2=CH2 + H2O + conc.H2SO4 → C2H5OH

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8
Q

Explain the reaction of:

CH2=CH2 + H2O + conc.H2SO4 → C2H5OH?

A

1 ⦾ Conc. H2SO4 reacts with ethene in nucleophillic addition - forms hydrogen sulfate
2 ⦾ Add cold water + warm product - hydrolysed to form ethanol
⦾ H2SO4 not used up - catalyst

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9
Q

Explain (fully) the mechanism for the electrophillic addition reaction below:
CH2=CH2 + H2O + conc.H2SO4 → C2H5OH?

A

1 ⦾ C=C attacks 𝛿+H on H2SO4
2 ⦾ Bond formed between Cs and H
3 ⦾ e-s from O-H bond taken by O to form lone pair
4 ⦾ 2nd C left with +ve charge as e- lost from double bond
5 ⦾ -ve ion created acts as nucleophile + attacks carbocation creating new intermediate
6 ⦾ Water then added to produce sulfuric acid + ethanol

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10
Q

Explain how alkenes are able to decolourise bromine water?
What does it form?
Via which mechanism?

A

⦾ Bromine added across double bond
⦾ Form colourless dibromoalkane
⦾ Electrophillic Addition

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11
Q

What is the equation for the reaction of bromine water decolourising ethene?

A

H2C=CH2 + Br2 → CH2BrCH2Br

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12
Q

Explain (fully) the mechanism for the reaction between bromine water and ethene?

A

1 ⦾ C=C repels e- in Br2, polarising 𝛿+Br-𝛿+Br - induced dipole
2 ⦾ e- pair in C=C attracts 𝛿+Br and forms bond with it
3 ⦾ Repels e- in Br-Br further until bond breaks + 𝛿+Br bonds with it
4 ⦾ You get +vely charged carbocation intermediate
5 ⦾ Br- attracted
6 ⦾ Bonds to other C
⦾ Forms: 1,2-dibromoethane

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13
Q

What is the mechanism for the reaction between alkenes and hydrogen halides?

A

⦾ Electrophilic Addition

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14
Q

What does the reaction between alkenes and hydrogen halides form?

A

⦾ Hydrogen halides

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15
Q

Draw the mechanism for the reaction between ethene and hydrogen bromide?

A

⦾ pg. 218

⦾ C2H4 + HBr → C2H5Br

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16
Q

What happens if a hydrogen halide is added to an unsymmetrical alkene?

A

⦾ 2 possible products

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17
Q

Draw the mechanism for the reaction between propene and hydrogen bromide and the 2 possible products?

A

⦾ pg. 218
⦾ Br could be added to 1st or 2nd C
⦾ 1-bromopropane or 2-bromopropane

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18
Q

What are the 3 possible carbocation intermediates?

A

⦾ Primary carbocation (1 X R)
⦾ Secondary carbocation (2 X R)
⦾ Tertiary carbocation (3 X R)

19
Q

Which of the 3 carbocations is the most stable?

A

⦾ Tertiary

20
Q

Why is the tertiary carbocation the most stable?

A

⦾ Because the alkyl groups feed e-s towards the +ve charge

21
Q

How can you show an alkyl group is donating electrons to the +ve charge?

A

⦾ Draw arrow on bond that points to where e-s are being donated
⦾ pg. 219

22
Q

What can the product that there’s most of also be called?

A

⦾ Major product

⦾ (minor product)

23
Q

Draw out the mechanism for the reaction between Hydrogen bromide and propene?

A

⦾ H2C=CHCH3 + HBr → CH3CHBrCH3
⦾ H2C=CHCH3 + HBr → CH2BrCH2CH3
⦾ Secondary carbocation more stable - 2 alkyl groups

24
Q

Draw out the mechanism for the reaction between Hydrogen bromide and 2-methylbut-2-ene?

A

⦾ pg. 220

25
Q

What can also affect how much of the major product forms in the end?

A

⦾ bigger difference in stability of carbocations

26
Q

Define polymer?

A

⦾ Natural e.g. DNA

⦾ Synthetic e.g. polyethene

27
Q

How are addition polymers formed?

A

⦾ Alkenes where the double bond is broken to form repeating unit.

28
Q

What should you remember when drawing a monomer in polymer form?

A

⦾ -(-x-x-)-n

29
Q

What does n stand for?

A

⦾ N = no. of repeating units in a polymer

30
Q

What should you do if you’re asked for the formula of a polymer?

A

⦾ Include brackets and n

31
Q

What should you do if you’re asked for the repeating unit?

A

⦾ Just bit inside bracket

32
Q

How do you find the monomer used to form an addition polymer?

A

⦾ Take repeating unit
⦾ Remove side/trailing bonds
⦾ Add double bond

33
Q

How do you name addition polymers?

A

⦾ Find monomer

⦾ poly(X)

34
Q

How would you name the addition polymer for

but-2-ene?

A

⦾ poly(but-2-ene)

35
Q

What will altering the reaction conditions for the production of plastic polymer chains do?

A

⦾ Give different properties

36
Q

What conditions produce branched chain polymers?

A

⦾ Weak IMFs between branched chain polymers
⦾ High pressures
⦾ High temps

37
Q

What conditions produce straight polymers?

A

⦾ Strong IMFs
⦾ Lower pressures
⦾ Lower temps

38
Q

What are the features of polymers?

A

⦾ Unreactive HC chains
⦾ Lots of strong
⦾ Non-polar
⦾ Covalent bonds

39
Q 
Give an everyday use of polymers?
Which poly(X)?
A

⦾ Shopping bags

⦾ poly(ethene)

40
Q

What is a disadvantage of addition polymers (for plastic in particular)?

A

⦾ Unreactive nature of bonds
⦾ Therefore not biodegradable
⦾ Cannot be broken down

41
Q

What is PVC?

A

⦾ Poly(chloroethene)
⦾ Addition polymer
⦾ Waterproof properties

42
Q

How does PVC gain its waterproof property?

A

⦾ Addition of plasticisers during reaction

43
Q

How does plasticiser make a polymer bendier?

A

⦾ Gets between polymer chains + pushes apart

⦾ Reduces strength on IMFs

44
Q

What are the uses of PVC?

A

⦾ Electrical cable insulation
⦾ Floor tiles
⦾ Clothing

CHEMISTRY (AS) (24 decks)

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