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A Level Chemistry OCR > Ch13 Alkenes > Flashcards

Ch13 Alkenes Flashcards

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1
Q

What is an alkene?

A

Alkenes are unsaturated hydrocarbons that contain at least 1 C=C bond (functional group).
Alliphatic alkenes w/ 1 = have general formula CnH2n
Alkenes can be branched, cyclic and contain 1+ double bond.

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2
Q

What is an alkene?

A

Alkenes are unsaturated hydrocarbons that contain at least 1 C=C bond.
Alliphatic alkenes w/ 1 = have general formula CnH2n
Alkenes can be branched, cyclic and contain 1+ double bond.

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3
Q

Explain sigma + pi bond

Explain the formation of the double bond in alkenes:

A

C=C double bond is comprised of a sigma bond (σ) and a pi bond (π).

σ bond: formed by overlap of orbitals directly between bonding carbon atoms.

π bond: formed by sideways overlap of adjacent p-orbitals above and below bonding C atom.

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4
Q

Define Stereoisomers:

A

Stereoisomers are compounds with the same structural formula but different arrangement of atoms in space.

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5
Q

Why do E/Z stereoisomers occur?

A

E/Z isomerism around C=C arises due to the restricted rotation around double bond which fixes the group attached to each C atom in position.

Rigidity of double bond due to π bon’s electron density being concentrated above and below the plane of σ bond.

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6
Q

What conditions permit the occurence of an E/Z isomer?

A

2 conditions must be met:
1. C=C double bond
2. different groups attached to each C atom of double bond.

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7
Q

Describe E/Z isomerism:

A
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8
Q

Why are alkenes more reactive than alkanes?

A

Alkenes are more reactive because the π bond is weaker than σ bond, as π requires less energy to break.
When alkenes react, π bond breaks but σ bond remains intact.

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9
Q

What kind of reaction do alkenes undergo?

A

Alkenes undergo electrophillic addition reactions

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10
Q

draw

Describe the hydrogenation of alkenes:

A
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11
Q

Describe the halogenation of alkenes:

A
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12
Q

What is the test for unsaturation in alkenes?

A
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13
Q

Describe the addition of hydrogen halide to alkenes:

A
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14
Q

Describe the addition of hydrogen halide on unsymmetrical alkenes:

A
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15
Q

Describe the hydration of alkenes:

A
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16
Q

Describe the addition of steam to unsymmetrical alkenes:

A
17
Q

Define ‘Electrophiles’:

A

Electrophiles - electron pair acceptors.
Usually + ions/molecules where one of the atoms has partial positive charge.

18
Q

Draw the mechanism for electrophillic addition of bromine to an alkene:

A
19
Q

What is Markownikoff’s Rule of carbocation?

A

When an unsymmetrical alkene reacts with an unsymmetrical molecule, there are 2 possible isomeric products.

1st step of mechanism- carbocation is formed as intermediate (stage)

The major product will be formed from more stable carbocation

20
Q

What are the 3 different classifications of carbocations?

A
21
Q

Describe and explain the differing stability of carbocations:

A
22
Q

Draw the mechanism for electrophillic addition of an unsymmetrical molecule to an unsymmetrical alkene:

A
23
Q

What is addition polymerisation?

A
  • Polymerisation is carried out at high temperatures and pressures using catalysts.
  • A polymer is a large molecule formed from many thousands of repeat units of smaller molecules known as monomers.
  • Place bracket around one unit and add ‘n’ next to it for repeating units.
24
Q

What is the structure and different uses of Poly(ethene)

A
25
Q

What is the structure and different uses of Poly(propene)?

A
26
Q

What is the structure and different uses of Poly(chloroethene)?

A
27
Q

What is the structure and different uses of poly(phenylethene)?

A
28
Q

What is the structure and different uses of Poly(tetrafluoroethene)?

A
29
Q

Why are polymers of alkenes a cause for environmental concern?

A
  • Alkene-based polymers: non-biogradeable, so there are problems for safe disposal.
30
Q

Describe ‘Recycling’ as a method of polmer waste disposal:

A
  • Involves sorting polymer waste into different types before chopping into flakes, washing, drying, melting + reshaping for repurposing.
  • Conserves finite fossil fuels and decreases amount of waste sent to landfill
31
Q

What is a problem of disposing PVC?

A
  • PVC contains range of additives and high Cl content
  • Sending to landfill not sustainable
  • Burning PVC releases corrosive HCl gas and other pollutants
  • e.g. toxic dioxins
  • PCV polymers are now recycled by dissolving in solvents and recovering them from solvent by precipitation.
32
Q

Describe ‘using waste polymers as fuel’ as a method of reusing polymers:

A
  • polymers can be incinerated to produce heat + generate steam to drive turbines and produce electricity.
33
Q

Describe using waste polymers as organic feedstock as a method of reusing polymers:

A
  • Chemical + thermal processes can be used to reclaim monomers, gases or oil from waste polymers.
  • Reclaimed products can be used as raw materials for production of new polymers
  • Feedstock recycling advantage: being able to handle unsorted + unwashed polymers
34
Q

What are bioplastics?

A
  • Bioplastics are biodegradable polymers produced from plant starch, celulose, plant oils + proteins.
  • Bioplastics are renewable and sustainable.
  • Can be broken down by microorganisms into water, CO2, and biological compounds.
  • Bioplastics help protect environment + conserve valuable oil reserves
35
Q

What are photodegradable polymers?

A
  • Photodegradable polymers contain bonds that weaken when light absorbed - start process of degradation.

A Level Chemistry OCR (27 decks)

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