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A Level Chemistry > Organic Chemistry - Topic 6.1 - 6.2 > Flashcards

Organic Chemistry - Topic 6.1 - 6.2 Flashcards

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1
Q

What are organic molecules

A

Covalent molecules based on the element carbon

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2
Q

What is the hydroxyl functional group

A

OH

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3
Q

What is the functional group

A

A group of atoms which gives an organic compound its characteristic properties and determines how it reacts

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4
Q

What is a homologous series

A

A series of Organic molecules with the same functional group but each successive member has an additional CH2

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5
Q

Why can carbon form so many compounds

A
  • carbon can form chains, chained branches and rings of varying sizes which other molecules can attach to
  • Carbon forms inert bonds with C-C and C-H due to its relatively high bond enthalpy
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6
Q

What are saturated hydrocarbons

A

Hydrocarbons with only single covalent bonds between carbon atoms

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7
Q

What is an unsaturated hydrocarbon

A

A hydrocarbon with a double or triple bond

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8
Q

Prefixes for alkanes and number of carbon atoms up to 10 carbon atoms

A

Meth - 1 c atoms
Eth - 2 c atoms
Prop - 3 c atoms
But - 4 carbon atoms
Pent - 5 carbons atoms
Hex - 6 c atoms
Hept - 7 carbon atoms
Oct - 8 c atoms
Non - 9 c atoms
Dec - 10 c atoms

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9
Q

Why are alkanes unreactive

A
  • they are non polar as carbon atoms and hydrogen atoms have similar Electronegativity
  • the bonds are relatively strong and require a lot of energy to break
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10
Q

What is a free radical

A

Any species with an unpaired electron

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11
Q

Stages in the free radical substitution with methane and bromine

A

1) initiation stage
UV light is shon onto the bromine molecule, the energy of the UV light causes the single covalent bond between the two bromine atoms to break. When the bond breaks each electron from the covalent bond (as one covalent bond consists of a pair of electrons) goes to each bromine atom, and as they have unpaired electrons they form bromine free radicals
Br- Br → Br. + Br.
When a covalent bond splits this way scientist calls it homolytic fission
2) Propagation stage
1st step - a bromine free radical reacts with a methane molecule and forms a covalent bond by taking a hydrogen atom(with its electron in the hydrogen atom) from the methane to form hydrogen bromide and a methyl free radical (as the carbon atom will have an unpaired electron)
2nd step - the methyl free radical reacts with a bromine molecule producing bromomethane and another bromine free radical, this causes a chain reaction as the bromine free radical in step 2 can be used in step one to react with methane until it reaches the termination stage
3) termination stage
Two bromine free radicals react together to form a bromine molecule with no free radicals
OR
Two methyl free radicals can form a molecule of ethane
OR
A methyl free radical and a bromine free radical can form a molecule of bromomethane

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12
Q

Problems with free radical substitution with bromine and methane

A

A lot of side products can form
E.g
Bromomethane + bromine free radical → dibromomethane
Dibromomethane + bromine free radical → tribromomethane
Tribromomethane + bromine free radical → tetrabromomethane

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13
Q

What is homolytic fission

A

When a covalent bond breaks evenly and each bonded atom takes one of the shared pair of electrons

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14
Q

General formulas for alkanes

A

CnH2n+2

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15
Q

What are the bond angles in alkanes

A

109.5 as they have a tetrahedral structure

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16
Q

What is the general formula of alkenes

A

CnH2n

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17
Q

Bond angles of alkenes

A

120

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18
Q

What does the double bond in alkenes consist of

A

A sigma bond and a pi bond

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19
Q

Properties of alkenes

A
  • as it contains a pi bond due to its double bond, the pi bond cannot rotate as any rotation will reduce the overlap of any p orbitals this means the alkenes can form stereoisomers
  • they are highly reactive as the bond enthalpy of the pi bond is less than the sigma bond as the pi bond is a sideways overlap of orbitals whilst a sigma bond is a direct overlap, meaning that it will take less energy to break the pi bond making alkenes very reactive
  • the double bond contains two pairs of electrons - one in the pi and one in the sigma - so the double bond is a region of high electron density making alkenes highly reactive
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20
Q

How do alkanes react

A

Free radical substitution

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21
Q

How do alkenes react

A

Electrophilic addition

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22
Q

Process of electrophilic addition of hydrogen halide and alkenes ( ethene and hydrogen bromide)

A

1) the hydrogen bromide molecule (which is already polar due to the bromine being more electronegative than the hydrogen) approaches the ethene, the electrophile (the positive hydrogen atom on the HBr) is attracted to the high electron density of the double bond and attracts the pair of electrons in the pi bond of the alkene, causing it to move towards the hydrogen atom in the HBr, but as the hydrogen atom can only form one covalent bond at the same time the pair of electrons between the hydrogen atom and bromine move onto the bromine atom, which is called heterolytic fission
2) this forms a positively charged carbocation intermediate (which contains a positively charged carbon atom) which is positively charged as it lost its electron pair that were in the pi bond (so it has lost its double bond and is now single bonded with an extra h atom from 1st step) and a negatively charged bromide ion
3) the electron pair on the bromide ion are attracted to the positive carbon atom in the carbocation and this electron pair forms a covalent bond with the bromide ion and the carbocation to form bromoethane

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23
Q

What is an electrophile

A

Any positive ion or molecule that is attracted to a region of high electron density

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24
Q

What is markowinoffs rule

A

when a hydrogen halide reacts with an asymmetric alkene the hydrogen halide is more likely to bond to the carbon atom with the greater number of hydrogen atoms attached to it

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25
Q

What is a carbocation intermediate

A

An unstable molecule that exist for a short period of time

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26
Q

What does the stability of the carbocation depend on

A

The number of alkyl groups bonded to the carbon atom with the positive charge

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27
Q

What is an alkyl group

A

A group containing carbon and hydrogen atoms

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28
Q

What is a primary secondary and tertiary carbocation

A

Primary- when there is only one alkyl groups attached to the positive carbon atom
Secondary- when there is two alkyl groups attached to the positive carbon atom
Tertiary - where there are three alkyl groups attached to the positive carbon atom

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29
Q

Why is the secondary carbocation more stable and more likely to form a major product than the primary carbocation

A

As there are more alkyl groups attached to the secondary carbocation so has a stronger inductive effect,this is because the greater number of alkyl groups means that more electrons are pushed towards the positive charge, this provides it better stability as the positive charge is more reduced and because of this extra stability the secondary cation is more likely to form, resulting in it to form a major product

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30
Q

How to tell which product is major or minor in electrophilic addition

A

The one with the most alkyl groups attached to it is the major product

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31
Q

What are structural isomers

A

Compounds with the same molecular formula but different structural formula

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32
Q

What are chain isomers, position isomers and functional isomers

A

Chain isomers- isomers with different chains of carbon atoms
Position isomers - isomers with different positions of the same functional group
Functional isomers - isomers with different functional groups

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33
Q

What are stereoisomers

A

Molecules with the same structural and molecular formula but have different spatial arrangements of bonds (arranged differently in space)

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34
Q

Types of stereoisomers

A

Geometrical isomers
Optical isomers

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35
Q

Naming systems for geometric isomers

A

E/Z isomerism
Cis/Trans isomerism

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36
Q

Why can alkenes only form cis/trans isomers

A

As they contain double bonds which cannot fully rotate but can only flex slightly

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37
Q

What conditions do alkenes have to have to form cis/trans isomers

A
  • carbon atoms on double bond must be attached to two different groups
  • one of the groups on both carbon atoms of the double bond must be the same
  • there must be a restriction to rotation about a bond
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38
Q

How to determine if cis or trans isomer

A

If the group which is the same on both carbon atoms in the double bond are on the same side then it’s a cis isomer and if its on different sides then it’s a trans isomer

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39
Q

CIP priority rules (for naming E/Z isomers with four different groups all attached to the carbon atoms involved in double covalent bonds)

A
  • the element with the greatest atomic number is given the higher priority on each side of the double bond
  • the we assign the higher priority groups using the E/Z isomerism if the higher priority groups are on the same side the it is an Z isomer and if the higher priority groups are in opposite sides it’s is the E isomer
  • if the carbon atom is attached to two of the same groups (e.g two o atoms) then we use the atom next to it (e.g in this case the next atom to o) to establish priority
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40
Q

Conditions for free radical substitution

A

UV light, room temperature

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41
Q

Electrophillic addition between bromine and ethene

A

1) Stage 1
The bromine approaches the ethene molecule and as the double bond of the alkene is a region of high electron density and this high electron density repels the electron pair of the covalent bond in the bromine molecule causing the bromine molecule to have an induced dipole
2) Stage 2
The pair of electrons in the pi bind if the alkene are attracted to the positive bromine (the electrophile) and the electron pair forms a covalent bid to the bromine atom and at the same time the pair of electrons in the bromine molecule break and the pair of electrons would move into the other bromine atom through heterlytic fission
3) Stage 3
The electron pair on the bromide ion is attracted to the positive carbon atom on the carbocation immediate this electron pair forms a covalent bond between the bromide ion and the positive carbon

42
Q

Test for unsaturated molecules

A

Add drops of Bromine water to test tube and gently shake
Orange to colourless

43
Q

Suffix for alcohol with one two or 3 alcohol functional groups

A

1 - ol
2 - diol
3 - triol

44
Q

What is a primary secondary and tertiary alcohol

A

Primary- the carbon atom bonded to the hydroxyl group is bonded to one other carbon atom
Secondary- the carbon atom bonded to the hydroxyl group is bonded to two other carbon atoms
Tertiary - the carbon atom bonded to the hydroxyl group is bonded to three other carbon atoms

45
Q

Equation for hydration reaction

A

Alkenes and steam forms an alcohol

46
Q

Conditions for hydration reaction

A

Temp 300 degrees Celsius
Pressure 60 atm
Catalyst phosphoric acid

47
Q

Hydration reaction of ethene

A

1) Stage 1
The pair of electrons in the pi bond of the ethene are attracted to one of the positive hydrogen atoms in the phosphoric acid which acts as an electrophile. The pair of electrons in the pi bond forms a covalent bond to the positive hydrogen atom and the covalent bond between the oxygen and hydrogen breaks and the pair of electrons move to the oxygen atom by heterolytic fission, forming a carbocation intermediate and a dihydrogen phosphate ion with a negatively charged oxygen atom
2)Stage 2
The carbocation intermediate reacts with a molecule of WATER (not the catalyst) in the form of steam one of the lone pairs of the o atom in the water forms a covalent bond with the positive carbon atom (as o has two lone pairs), forming an intermediate molecule with a positive oxygen atom, the o is positive as its lone pair of electrons has formed a covalent bond
3) Stage 3
The dihydrogen phosphate ion forms a covalent bond between the o of the phosphate and the hydrogen atom of the water molecule that attached to the intermediate molecule and at the same time the covalent bond between the hydrogen atom and the o atom of the water molecule breaks by heterolytic fission to form ethanol and phosphoric acid

48
Q

How do we know which carbon atom the phosphoric atom will bond to in hydration when there is an asymmetrical alkene

A

It will attach to the carbon with the greater number of hydrogen atoms

49
Q

Why are alkenes highly reactive molecules

A

Due to the double bond as it contains two pairs of electrons, one in the sigma bond and one in the pi, meaning that the double bond is a region of high electron density, this high electron density means that alkenes react by Electrophillic addition, plus the pi bond takes less energy to break than the sigma bond so the pi bond is more likely to take part in reactions

50
Q

What does the reaction, hydrogenation involve

A

Alkene and hydrogen gas to form an alkane

51
Q

Conditions for hydrogenation

A

Temp 150 degrees
Catalyst: nickel catalyst

52
Q

Important use of hydrogenation

A

Used to make margarine by hydrogenating vegetable oil, as the vegetable oil contains unsaturated fatty acids and by hydrogenating unsaturated fatty acids to turn them into saturated fatty acids we increase their melting point converting them from liquid oil to a solid margarine

53
Q

What does the oxidation by potassium magnate with alkenes form

A

A diol

54
Q

What happens in the oxidation by potassium maganate with alkenes

A

The dilute acidified potassium maganate converts the alkene to a diol at room temperature and at the same time the purple maganate ions are reduced yo a very pale pink maganate ion. if there is and excess of alkenes the purple colour will completely

55
Q

How are polymers formed

A

By joining thousands of small identical monomers

56
Q

What are the monomers that join to make addition polymers

A

Alkenes

57
Q

Conditions for polymerisation

A

High temp and pressure and a catalyst

58
Q

What are addition polymers

A

A molecule with a large number of carbon to hydrogen and carbon to carbon single bonds formed by the joining together of monomers

59
Q

Why can addition polymers last a long time in the environment

A

As the bonds are non polar and relatively strong which makes them difficult to break so they are unreactive so can last in the environment for a long time

60
Q

Environmental affects of addition polymers

A
  • they are non biodegradable due to them being unreactive so they cannot be broken down by microorganisms in the environment, causing them to pollute the environment for a long period of time, which is harmful to wildlife
  • they involve the use of crude oil which is non renewable as addition polymers are made from alkenes, and the crude oil needs to be transported and refined which requires energy
  • they are used in large mounts so occupy space and landfill
61
Q

Ways to reduce environmental affects of addition polymers

A
  • rather than sending waste polymers to landfill they can be combusted, generating energy, however this can release harmful chemicals such as PVC - when PVC is combusted it release HCl which is corrosive
  • polymer waste can be sorted into different polymers and recycled into new products, by recycling polymers we reduce the use of crude oil and the amount of waste in landfills
  • polymers can be recycled by feedstock recycling, this is where waste polymers are converted back to simpler hydrocarbons these hydrocarbons can then be cracked and converted to different polymers without needing to sort the polymers
  • developing biodegradable polymers using plant materials materials so that they can naturally break down due to the actions of microorganisms
62
Q

Advantages of feedstock recycling

A
  • does not need to sort different polymers
  • can convert one polymer to a different polymer
63
Q

Advantages of biodegradable polymers

A
  • manufactured from plant material which is a renewable source of energy
64
Q

How do sigma bonds form

A

When electron orbitals from adjacent atoms overlap

65
Q

Properties for alkanes

A
  • fully rotational as they only contain sigma bonds
  • unreactive as covalent bonds are relatively strong and take a lot of energy to break
  • insoluble in water as they are non polar so cannot form hydrogen bonds with water
66
Q

Why do longer chain alkanes have a higher boiling point than shorter chain alkanes

A
  • they have more electrons so stronger London forces
  • there surface area is larger for the formation of London forces so it takes more energy to break the London forces in the longer chain alkanes
67
Q

What happens in the fractional distillation of crude oil

A

1) the crude oil is vaporised in a furnace
2) the crude oils vapours move up the fractioning column, the column is hotter at the bottom and becomes cooler at the top
3) as each alkane moves up the column at some point it will reach a temp which is cooler than its bp causing it to condense back to liquid and pass out of the column,
4) the alkanes with shorter carbon chains condense near the top of the column due to their low bp whilst the longer chain alkanes condense at the bottom due to their high bp and alkanes with very long chains form a thick liquid called bitumen which is collected from the very bottom

68
Q

What’s does fractional distillation do

A

Separates the crude oil into fractions that contain alkanes with similar boiling points

69
Q

Order of fuels releases in a fractioning column from the highest boiling point (the bottom) to the lowest boiling point (the top)

A

Bitumen, fuel oil, lubricating oil, diesel, kerosene, petrol/naptha, refinery gases

70
Q

Problems with fractional distillation

A

It produces a higher proportion of longer chain alkanes which is in less demand

71
Q

Benefits of cracking

A
  • converts long chain hydrocarbons to shorter chain hydrocarbons
  • it produces alkenes which are highly reactive
72
Q

Methods of cracking

A

Thermal cracking
Catalytic cracking

73
Q

Conditions for thermal cracking

A
  • requires a high temperature of 900 degrees and a high pressure of 70 atm
74
Q

What happens in thermal cracking

A

In The long chain alkanes a covalent bond between two carbon atoms split to form intermediate molecules so both intermediate molecules become free radicals as they both have one unpaired electron these free radicals then form shorter chain alkanes and alkenes (and hydrogen)

75
Q

Advantages of thermal cracking

A

There is a high percentage of alkenes in the products

76
Q

Conditions for catalytic cracking

A

Temp 450
Pressure 2 atm
Catalyst zeolite (a mixture of aluminium oxide and silicon oxide)

77
Q

What products are formed in catalytic cracking

A
  • branched chain alkanes, cyclic alkanes and aromatic hydrocarbons
78
Q

name of reaction between an unsaturated molecule and another molecule

A
  • addition reaction
  • hydrolysis reaction
79
Q

names of reactions between a saturated molecule and another molecule

A
  • elimination reaction
  • substitution reaction
  • hydrolysis reaction
80
Q

what is an addition, substitution elimination and hydrolysis reaction

A

addition - where two molecules add together to form a single product
substitution - where one atom r group is replaced by another atom or group
elimination - a reaction which produces an unsaturated product by the loss of atoms or groups from adjacent c atoms
hydrolysis - a reaction in which a compound splits apart in a reaction involving water

81
Q

what is heterolytic fission

A

heterolytic - when the covalent bond breaks so only one atom takes both electrons

82
Q

what is a nucleophile

A

nucleophile - A nucleophile is an electron-rich species that can donate a pair of electrons to form a chemical bond in a reaction and are generally negatively charged or are neutral with a lone pair of electrons available for donation

83
Q

types of hydrocarbons and what they are

A

aliphatic hydrocarbons - chains of branched or unbranched carbon atoms or rings of carbon atoms
aromatic hydrocarbons/ arenes - rings of carbon atoms in which there are delocalised electrons

84
Q

equation for complete combustion of alkanes

A

alkane + oxygen —-> carbon dioxide + water

85
Q

incomplete combustion equation of alkanes

A

alkane + oxygen —-> carbon monoxide +carbon + water

85
Q

what happens to petrol after fractional distillation

A
  • it is refined to remove sulfur compounds to reduce pollution and is blended carefully to ensure smooth combustion to increase the octane number by increasing the proportions of branched alkanes and arenes or oxygen compounds
86
Q

methods used to increase octane number

A
  • cracking
  • reforming
  • adding ethanol and ethers
87
Q

what is reforming

A

a process where it converts straight chain alkanes into branched chain alkanes, cyclic alkanes or arenes

88
Q

conditions for reforming

A

catalyst: platinum
temp: 500
high pressure

89
Q

dangers of incomplete combustion

A
  • carbon monoxide - combines with haemoglobin so that the blood carries less o, causing body to be deprived of o which can strain the heart and kill
  • soot - can penetrate deep into lungs causing short term symptoms such as coughing and headache but long term exposure can cause heart disease and lung cancer
  • unburnt hydrocarbons - can contribute to photochemical smog which is when the unburnt hydrocarbons react with the sunlight
90
Q

dangers from impurities in fuels

A
  • sulfur - can lead to acid rain if reacted with o in the air and can damage the catalyst in catalytic converters
91
Q

dangers of high temperatures in engines

A
  • there is a sufficient activation energy for nitrogen, N to react with o to form nitrogen monoxide or nitrogen dioxide (which are both referred to as NOx) which can react with water and more o to form nitric acid which can lead to acid rain or can form ozone as in the bright sunlight the nitrogen dioxide breaks down to nitrogen monoxide and o radicals which react with o to form ozone, which can lead to photochemical smog
92
Q

how do catalytic converters help with pollutants

A
  • they imprve the air quality by removing pollutants that is released by carss exhausts by reacting the co and the unburnt hydrocarbons with the nitrogen oxides to form co2 and h20
93
Q

how can engines that burn petrol or diesel pollute the air

A
  • they do not burn completely
  • the fuel contains impurities
  • they run at high temperatures
94
Q

disadvantages of fossil fuels

A
  • non renewable as as they are being consumed faster than they are being replenished
  • produce carbon dioxide and enhance the greenhouse gas effect
95
Q

two main types of biofuels and how they are made

A
  • bioethanol - fermenting carbs and sugar
  • biodiesel - extracting and processing oils from crops
96
Q

ways to reduce co2 emissions from fossil fuels

A

biofuels - crops take in co2 for photosynthesis to make sugars and veggie oils that can be used to make biofuels, so when the biofuels burn the co2 that is taken up during photosynthesis is returned to the air so biofuels should have no effect on levels of co2 making it carbon neutral

97
Q

comparison between bioethanol and biodiesel

A
  • biodisel reduce more emissions than bioethanol as energy is not needed for distillation during the production of the fuel
  • conditions in bioethanol are more favourable as ethanol is manufactured by fermenting sugar from sugar canes and the refineries that make bioethanol meet all the energy demands
  • bioethanol causes large scale deforestation for sugar cane plantations
98
Q

disadvantage of biofuels

A
  • when landuse is switched from food crops to biofuel crops food prices rise and food production is displaced elsewhere causing cropland expansion elsewhere decreasing biodiversity
99
Q

why do alkenes with the same num of c atom than an alkane burn with a smokey flame

A

as they have a higher percentage of c atoms

100
Q

how is high (HDPE) and low density poly(ethene) (LDPE) formed

A

LDPE - by heating ethene at high pressure and temp with initiators, that have weak 0 to 0 bonds that break homolytically to form free radicals which then carries on to a free radical substitution reaction to form a long chained poly(ethene) with lots of branches preventing it to be packed closely together making it low density
HDPE - uses low temp and pressure with a catalyst to produce long chains that are closely packed together

A Level Chemistry (16 decks)

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