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Chemistry (m) Module 4 > Chapter 13 > Flashcards

Chapter 13 Flashcards

1
Q

Which is more reactive alkenes or alkanes

A

Alkenes

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2
Q

What is a double C-C bond made from and what does it prevent

A

A sigma bond (strong) and a pi bond (weak)
The pi bond fixes the carbon atoms in position at either end of the double bond preventing rotation

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3
Q

How is the double carbon to carbon bond formed

A

Each carbon Uses 3 of its electrons in the formation of sigma bonds amd one electron in the pi bond ( the two p orbitals overlap)

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4
Q

What is the shape and bond angle of an alkene molecule

A

Trigonal planar 120 degrees

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5
Q

For EZ isomerism what must a molecule have

A

A double c-c bond

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6
Q

Define stereoisomers

A

Compounds with the same structural formula but with a different arrangement of atoms in space

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7
Q

What is EZ isomerism

A

Different groups attached to each carbon of a c=c may be arranged differently in space due to the restricted rotation of the double bond

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8
Q

What is an E isomer

A

When groups are on opposite sides of the horizontal line

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9
Q

What is a z isomer

A

Where groups are on the same side of the horizontal line

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10
Q

What is different about cis trans isomerism

A

There must be a hydrogen on each of the carbons in the double bond

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11
Q

What is a cis isomer

A

H atoms on the same side of the horizontal line

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12
Q

What is a trans isomer

A

When the h atoms on each carbon are on different sides of the horizontal line

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13
Q

What is cahn-ingold-prelog nomenclature

A

Groups on the double bond are given priority based on atomic number. The higher the atomic number the higher the priority. If all the immediate have the same you move onto the next eg the H in CH3
If The highest priority groups are on the same side they are z isomers
If they are opposite it is an E isomer

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14
Q

Explain why there is no cis or trans pentane

A

There is full rotation about a single bond in alkanes so any different orientation of molecules does not constitute a different molecule. The double bond in alkenes inhibits free rotation so the molecule has to be broken to place the atoms attached to the carbon atoms in a different atom in a different location within the molecules

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15
Q

What happens to the sigma and pi bond when an alkene reacts

A

The pi bond breaks
The sigma bond remains intact

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16
Q

What does a diene contain eg buta13diene

A

2 c-c double bonds

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17
Q

Conditions for hydrogenation and name

A

Nickel catalyst
150 degrees Celsius
Reduction reaction

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18
Q

Conditions for halogenation and example

A

Room temp
Bromine water- test for alkenes orange —> colourless

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19
Q

Describe the addition of hydrogen halides to an alkene

A

Bubbled at room temp into liquid alkenes
Ethene + HBr ——> bromoethane

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20
Q

What is different during the halogenation of an unsymmetrical alkene

A

Eg propene
There are 2 possible products depending on which carbon the chlorine binds to, 1 or 2

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21
Q

Addiction of unsymmetrical alkenes ( add HBr)

A

Leads to a mixture of products one major one minor
Eg propene + HBr = 2-bromopropane(major) or 1-bromopropane (minor)

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22
Q

Alkene and steam
Conditions
Use

A

High temp and pressure and phosphoric acid catalyst
Used to make alcohols
Alkene + steam ——> alcohol

23
Q

Define electrophile

A

An atom or group of atoms that is attracted to an electron rich centre and accepts an electron pair

24
Q

What is electrophilic addition

A

The mechanism of when Alkenes take part in addition to form saturated compounds

25
How does the elctrophillic addition work in an alkene
Double bond in alkene represents region of high electron density due to the pi electrons Electrophiles attracted to the pi electrons
26
Describe the diagram for the addition of hydrogen bromide mechanism
Step one Arrow comes from middle of double bond in ethene to the hydrogen in hydrogen bromide An arrow from the middle of the bond with H and Br goes to Br. H has a slightly positive charge and Br has a slightly negative - HBr goes through Heterolytic fission This forms a carbocation which is an ethane molecule with one less hydrogen and so one carbon is slightly positive and a bromide ion ( as it accepted both electrons from the hydrogen) Step 2 The bromide ion is attracted to the slightly positive carbon in the ethene and bromoethane is formed
27
Addition of bromine to an alkene mechanism
Same diagram as with hydrogen bromide However The pi bond repels the electrons in the closest bromine atom inducing a charge in the Br2 as the electrons are pushed to the bottom Br The bromide molecule breaks by Heterolytic fission
28
What is markownikoff’s rule
When a hydrogen halide reacts with an unsymmetrical alkene the hydrogen of the hydrogen halide attaches itself to the carbon atom of the alkene with the GREATER NUMBER OF HYDROGEN AROMS and the SMALLER NUMBER OF CARBON ATOMS
29
How do the mechanisms change when it is a major or minor product
For a major product a secondary cation is formed For a minor product a primary cation is formed
30
What is a primary carbocation
The c+ is bonded to two hydrogens and an alkyl group
31
What is a secondary carbocation
A c+ bonded to two alkyl groups and one hydrogen
32
What is a tertiary carbocation
A c+ attached to three alkyl groups
33
What does the stability of carbocations depend on
The more alkyl groups attached to the carbocation the more stable it is
34
Why are carbocations most stable with more alkyl groups
Each alkyl group pushes electrons towards the carbocation The positive charge is thus spread out over the alkyl groups The more alkyl groups attached the more spread out the charge making the molecule more stable
35
What happens during addition of H2SO4
C=c opens up amd added on are one H and one O-SO2OH ( One single bond vertically down to an S form the O then two double bonds left and right to O then vertically from s a single bond to an oh group When the O-SO2OH is left on its own the top O has a lone pair which the curly arrow comes from
36
Conditions and description of addition of water with a strong acid to an alkene
Acid catalyst eg H2SO4 First add the H2SO4 to the alkene like previously described. Then swap it for the OH group
37
Define polymer
Long chain molecule made from many repeating units
38
Define monomer
Small molecule the combines with many other monomers to form a polymer
39
Radical polymerisation Conditions Products
200 degrees Very high pressure Can lead to branching of the polymer chain and polymer mixtures Eg poly(styrene)
40
The Ziegler Natta process Conditions Products
60mdegrees Specialist catalysts eg TiCl3 Conversion is low amd unreacted alkene is recycled Eg non branched poly(ethene)
41
Conditions to make low density poly ethene
200 degrees 2000 atm O2 Molecules loosely packed due to branching Flexible soft Plastic bags and cling film
42
Conditions to make high density poly ethene
60 degrees 2 atm Ziegler natta Molecules tightly packed Stiffer and harder Buckets and bottles
43
44
Advantages of polymers
Cheap Readily available More convenient Lack of reactivity- can store food and chemicals safely
45
Why are many alkene based polymers non biodegradable
They are stable molecules due to the strength of the C=C
46
Why is recycling polymers good and how do you do it
Reduces environmental impact, conserves finite fossil fuel Sort into types then chopped washed dried and melted down
47
Why can’t you recycle PVC normally amd what do you do
Hazardous due to high chlorine content Cannot be put in landfills or burnt as hydrogen chloride is released= corrosive Have to use solvents to dissolve polymer which can be reused
48
What can waste polymers be used to do
Incinerated to produce heat generating steam to drive a turbine producing electricity
49
What is feedstock recycling
The chemical and thermal process that can reclaim monomers, gases or oil from waste polymers Products resemble those from a crude oil refinery The materials can be used as raw materials for the production of new polymers
50
Advantages of feedstock recycling
Able to use unsorted and unwashed polymers
51
What are bioplastics and why are they good
Produced from plant starch, cellulose, plant oils and proteins that offer a renewable and sustainable alternative to oil based products Protects environment and conserves oil reserves
52
What are biodegradable polymers broken down by What are they based on commonly
Microorganisms into water carbon dioxide and biological compounds Leaves no visible or toxic residues Based of poly (lactic acid)
53
What are photodegradable polymers
Contain bonds that are weakened by absorbing light to start the degradation. Alternatively light absorbing additives are used
54
What is an electrophile
An electron pair acceptor

Chemistry (m) Module 4 (4 decks)

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