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A Level Chemistry > Topic 6: Organic Chemistry I > Flashcards

Topic 6: Organic Chemistry I Flashcards

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1
Q

Define displayed formula

A
  • shows how all the atoms are arranged and all the bonds between them
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2
Q

Define skeletal formula

A
  • shows the bonds of the carbon skeleton only, with any functional groups - hydrogen and carbon atoms aren’t shown
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3
Q

Define homologous series

A
  • a group of organic compounds that have the same functional group and general formula
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4
Q

What is a functional group

A
  • a group of atoms in a molecule responsible for the characteristic reactions of that compound
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5
Q

Give the definition of general formula

A
  • an algebraic formula that can describe any member of a family of compounds
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6
Q

Definition of molecular formula

A
  • the actual number of atoms of each element in a molecule
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7
Q

Definition of structural formula

A
  • shows the arrangement of atoms carbon by carbon with the attached hydrogens and functional groups - e.g. CH3CH2CH2CH2OH
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8
Q

What is the definition of empirical formula?

A
  • the simplest whole number ratio of atoms of each element in a compound
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9
Q

What are structural isomers?

A
  • two molecules that have the same molecular formula but different structural formulae
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10
Q

Describe chain isomers

A
  • the carbon skeleton can be arranged differently
  • e.g. straight or branched
  • these isomers have similar chemical properties but their physical properties will change due to the shape of the molecule
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11
Q

Describe positional isomers

A
  • the skeleton and the functional group could be the same, only with the functional group attached to a different carbon atom
  • also have different physical properties and possibly different chemical properties
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12
Q

Describe functional group isomers

A
  • the same atoms can be arranged into different functional groups
  • they have very different physical and chemical properties
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13
Q

What is stereoisomerism?

A
  • they have the same structural formulae but have a different spatial arrangement of atoms
  • alkenes can exhibit E-Z stereoisomerism
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14
Q

How do E-Z isomers arise?

A
  • there is restricted rotation around the C=C double bond
  • there are two different groups/atoms attached both ends of the double bond
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15
Q

What are alkanes

A
  • they are saturated hydrocarbons
  • general formula CnH(2n+2)
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16
Q

How does fractional distillation work?

A
  • oil is pre-heated then passed into the column
  • fractions condense at different heights
  • temperature of column decreases upwards
  • separation depends on boiling pint
  • boiling point depends on sie f molecules
  • the larger the molecule, the larger the London forces
  • similar molecules condense together
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17
Q

Order the fractions of alkane molecules in a fractionating column

A
  • fuel gas C1-C4
  • petrol
  • naphtha C5-C10
  • kerosene C10-C16
  • diesel oil C15-19
  • mineral oil C20-30
  • fuel oil
  • wax, grease
  • bitumen
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18
Q

What is cracking?

A
  • converting large hydrocarbons too smaller molecules by breaking C-C bonds
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19
Q

Why is cracking needed?

A
  • petroleum fractions with shorter C chains are in more demand
  • products of cracking are more useful and valuable than starting materials (e.g. ethene is useful)
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20
Q

What are the two types of cracking?

A
  • thermal cracking
  • catalytic cracking
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21
Q

Describe thermal cracking

A
  • takes place at high temp of around 1000 ºC
  • high pressure (70 atm)
  • produces lots of alkenes
  • these alkenes make polymers
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22
Q

Describe catalytic cracking

A
  • uses zeolite catalyst (hydrated aluminosilicate)
  • at a slight pressure
  • high temp 450 degrees
  • mostly produces aromatic compounds (contain benzene rings) and motor fuels
  • using catalyst cuts cost because it can be done at lower pressure and temp
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23
Q

What is reforming

A
  • converting straight-chain alkanes into branched chain alkanes and cyclic hydrocarbons
  • using catalyst (platinum stuck on aluminium oxide)
  • at 500 degrees
  • H2 gas produced
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24
Q

What is knocking

A
  • where alkanes explode on their own accord
  • straight-chain alkanes most likely to cause knocking
  • adding branched chains and cyclic hydrocarbons making knocking less likely so combustion more efficient
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25
Q

Are combustion reactions exothermic or endothermic?

A
  • exothermic
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26
Q

What are the products of complete combustion of alkanes?

A
  • CO2 and H2O
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27
Q

What are the products of incomplete combustion of alkanes?

A
  • CO and/or C and H2O
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28
Q

Describe how oxides of sulfur can cause environmental damage

A
  • some molecules in crude oil contain atoms of sulfur
  • during combustion of alkanes, sulfur forms sulfur dioxide and then reacts with the atmosphere to form sulfur trioxide
  • S + O2 → SO2
  • 2SO2 + O2 → 2SO3
  • these gases are acidic oxides and dissolve in water in the atmosphere to form sulfurous acid and sulfuric acid:
  • SO2 + H2O → H2SO3
  • SO3 + H2O → H2SO4
  • these contribute to the formation of acid rain, damaging aquatic life, crops, forests, buildings
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29
Q

How can oxides of nitrogen contribute to environmental damage?

A
  • nitrogen oxides form from the reaction between N2 and O2 inside the car engine
  • the high temperature and spark provides sufficient energy to break the strong N2 bond
  • N2 + O2 → NO
  • N2 + 2O2 → NO2
  • nitrogen dioxide is acidic and can dissolve in water to form nitrous acid and nitric acid:
  • 2NO2 + H2O → HNO2 + HNO3
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30
Q

Describe catalytic converters and how they work

A
  • a ceramic honeycomb coated with a thin layer of catalyst metals platinum, palladium, rhodium, giving a large surface area
  • removes CO, NOx and unburned hydrocarbons, turning them into CO2, N2, H2O
  • e.g. 2NO + 2CO → N2 + 2CO2
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31
Q

What are two examples of biofuels?

A
  • biodiesel: produced by reacting vegetable oils with a mixture of alkali and methanol
  • bioalcohols: produced from the fermentation of sugars from plants
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32
Q

What are the advantages and disadvantages of biofuel?

A

Advantages:

  • renewable, so reduction of use of finite fossil fuels
  • more carbon-neutral
  • allows fossil fuels to be used as feedstock for organic compounds
  • no risk of large scale pollution from exploitation of fossil fuels

Disadvantages:

  • less food crops can be grown
  • rainforests have to be cut down for land
  • shortage of fertile soils
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33
Q

What do alkanes react with halogens to form?

A
  • halogenoalkanes
34
Q

What are radicals?

A
  • a reactive species with an unpaired electron
35
Q

Describe free radical substitution reactions of alkanes

A

Initiation:

  • UV light supplies the energy to break the Cl-Cl bond by homolytic fission
  • this forms two chlorine free radicals
  • Cl2 → 2Cl•

Propagation:

  • the chlorine free radical removes an H from alkane forming an alkyl free radical
  • the alkyl free radical reacts with a Cl2 molecule to produce the main product and another Cl free radical
  • CH4 + Cl• → HCl + •CH3
  • •CH3 + Cl2 → CH3Cl + Cl•

Termination:

  • collision of two free radicals does not generate further free radicals
36
Q

What is the problem with free radical substitution and how to solve?

A
  • it’s hard to get a particular product as you end up with a mixture of products
  • you may end up with dichloromethane, trichloromethane, tetrachloromethane, chloromethane
  • solve by having an excess of methane
  • another problem is that radical substitution can occur at any point along the carbon chain so a mixture of structural isomers can be formed
37
Q

How do you write propagation steps for substituting a halogen on a ‘middle’ carbon?

A
  • make sure to put the free radical dot on the correct carbon
38
Q

Describe the bonding in alkenes

A
  • C=C double covalent bond consists of one sigma and one pi bond
  • pi bonds are exposed and have high electron density (they are electrophiles)
39
Q

What is the strongest type of covalent bond?-

A
  • sigma bonds
  • high electron density between the nuclei means there is a strong electrostatic attraction between the nuclei and shared pair of electrons
  • sigma bonds have a high bond enthalpy
40
Q

What type of bond are single covalent bonds in organic molecules?

A
  • sigma bonds
  • when two orbitals overlap
  • gives highest possible electron density
41
Q

Which bond has restricted rotation?

A
  • pi bonds
42
Q

What is an addition reaction and what molecules tend to undergo these?

A
  • a reaction where two molecules react together to produce one
  • alkenes tend to undergo addition reaction because the pi-bond electrons are used to form new bonds with an attacking molecule
  • the product contains sigma bonds, not pi bonds, so the bonds in the product are stronger and more stable
43
Q

Describe reaction of alkenes → alcohols

A
  • alkenes are hydrated by steam
  • at 300 degrees
  • 60-70 atm
  • solid phosphoric (V) acid catalyst
  • done industrially, high atom economy
44
Q

Describe the reaction of alkenes with hydrogen

A
  • alkenes → alkanes
  • reagent: hydrogen
  • conditions: nickel catalyst
  • addition/reduction reaction
45
Q

What are electrophiles?

A
  • electron pair acceptors
  • often positively charged ions or partially positive areas
  • electron poor, so attracted to electron rich areas
  • react with negative ions, atoms with lone pairs and electron rich area around C=C double bond
46
Q

What is electrophilic addition?

A
  • happens to alkenes
  • the alkene double bond opens up and atom are added to the carbon atoms
  • happens because double bond has got many electrons and is attacked by electrophiles
47
Q

Describe the reaction of alkenes with bromine/chlorine

A
  • alkene → dihalogenoalkane
  • reagent: bromine/chlorine
  • conditions: room temperature
  • mechanism: electrophilic addition
48
Q

Briefly describe the addition of hydrogen halides to alkenes

A
  • alkene → halogenoalkane
  • reagent: HCl or HBr
  • conditions: room temp
  • electrophilic addition
49
Q

How do you oxidise an alkene?

A
  • alkene → diol
  • reagent: acidified KMnO4
  • conditions: room temp
  • observation: purple colour of MnO4- ion will decolourise to colourless
  • a test for alkene functional group
50
Q

What does bromine water test for?

A
  • presence of C=C
  • colour change from orange to colourless
51
Q

Describe the products of unsymmetrical alkenes addition reactions

A
  • there is a major and minor product
  • a primary and a secondary (or tertiary) carbocation is formed
  • carbocation stability is 3>2>1
  • because the methyl groups on either side of the positive carbon are electron releasing and reduce the charge on the ion, stabilising it
52
Q

What is addition polymerisation?

A
  • double bonds in alkenes open and join together to as make long chain called polymers
53
Q

What are polyethene and polypropene used for?

A
  • polyethene: flexible, easily moulded, waterproof, low density
  • plastic bags
  • buckets
  • bottles
  • polypropene: stiffer
  • utensils
  • ropes
  • carpets
54
Q

Describe and explain methods of disposal of waste polymers

A

Incineration:

  • rubbish is burnt and energy produced used in generating electricity
  • toxins are released on incineration
  • greenhouse gases emitted
  • volume of rubbish greatly reduced

Recycling:

  • saves raw materials
  • polymers need collecting/sorting, expensive
  • careful sorting needed

Feedstock for cracking:

  • Polymers can be cracked into small molecules which can be used to make other chemicals and new polymers
  • saves raw materials
55
Q

What are nucleophiles

A
  • they are electron pair donors - often negatively charged ions or a species that contain a lone pair of electrons - electron rich so attracted to electron poor areas - therefore, likely to reaction with positive ions and partially positive areas in molecules with polar bonds
56
Q

Give examples of nucleophiles that react readily with halogenalkanes

A
  • OH-
  • NH3
  • CN-
  • H2O
57
Q

What makes halogenoalkanes reactive?

A
  • the C-X bond is polar due to differences in electronegativity
  • carbon atom is slightly positive, so they attract nucleophiles
58
Q

What halogenoalkane are subsituted fastest and why?

A
  • iodoalkanes
  • the weaker the bonod, the easier it is to break and the faster the reaction
59
Q

What affects how quickly different halogenoalkanes hydrolyse?

A
  • the carbon-halogen bond enthalpy
  • weaker carbon-halogen bonds breaks more easily, so react faster
  • bond enthalpy depends on the size of the halogen
  • the larger the halogen, the longer the C-X bond, the lower the bond enthalpy
  • the size of the halogen increases down group 7, so iodoalkanes have the weakest bonds, so hydrolysed fastest
60
Q

Describe the reaction of halogenoalkanes with aqueous hydroxide ions

A
  • halogenoalkane → alcohol
  • reagent: potassium hydroxide
  • heat under reflux
  • nucleophilic substitution
61
Q

Which halogenoalkane undergoes SN2 mechanism and draw?

A
  • primary halogenoalkanes
62
Q

Which halogenoalkane undergoes SN1 mechanism and draw?

A
  • tertiary halogenoalkanes
63
Q

Describe the reaction of halogenoalkanes with ammonia

A
  • halogenoalkane → amine
  • reagent: NH3 dissolved in ethanol
  • heat under pressure
  • further substitution reactions can account between halogenoalkanes and amines
64
Q

Describe halogenalkanes reaction with alcoholic hydroxide ions

A
  • halogenoalkane → alkene
  • reagents: potassium hydroxide
  • conditions: in ethanol, heat
  • mechanism: elimination
65
Q

How do cyanide ions react with halogenoalkanes to form nitriles?

A
  • reflux a halogenoablkane with potassium cyanide in ethanol to form a nitrile by nucleophilic substitution
66
Q

What are the uses of halogenoalkanes?

A
  • refrigerants, fire retardants, pesticides, aerosol propellants
  • chloroalkanes are used as solvents
  • they are toxic and destroy the ozone layer
67
Q

Describe the combustion of alcohols

A
  • combust with a clean flame
  • CH3CH2OH + 3O2 → 2CO2 + 3H2O
68
Q

How do alcohols form halogenoalkanes?

A
  • Various halogenating compounds are used to substitute OH group for a halogen

-

69
Q

How do you form a bromoalkane from an alcohol?

A
  • substitution reaction with HBr
  • reaction requires an acid catalyst e.g. 50% concentrated H2SO4 and KBr
70
Q

How do you make iodoalkanes from alcohol?

A
  • reacting with phosphorus triiodide (PI3)
  • 3ROH + PI3 → 3RI + H3PO3
71
Q

What happens when you react alcohols with PCl5

A
  • produces chloroalkanes
  • ROH + PCl5 → RCl + HCl + POCl3
  • misty fumes produced (HCl)
72
Q

What happens when you react alcohols with HCl?

A
  • produces chloroalkanes
  • ROH + HCl → RCl + H2O
  • fastest rate with tertiary alcohols
  • slowest rate with primary alcohol
73
Q

Describe the dehydration of alcohols

A
  • alcohol → alkene
  • reagents: concentrated phosphoric acid
  • conditions: warm under reflux
  • elimination reaction
  • secondary and tertiary alcohols can give more than one product
74
Q

Why are there two possible alkene products when water from alcohols are eliminated?

A
  • depends on which side of the hydroxyl group the hydrogen is eliminated from
75
Q

What are carbonyl compounds?

A
  • have the functional group C=O
76
Q

Describe the oxidation of primary alcohols (partial then full)

A
  • reaction: primary alcohol → aldehyde → carboxylic acid
  • reagent: potassium dichromate(VI) solution and dilute sulfuric acid
  • conditions: warm gently and distil/heat under reflux
  • orange dichromate ion reduces to green Cr3+ ion
77
Q

Describe the oxidation of secondary alcohols

A
  • Reaction: secondary alcohol → ketone
  • reagent: potassium dichromate(VI) and dilute sulfuric acid
  • heat under reflux
  • orange to green
78
Q

How can you control how far the alcohol is oxidised?

A
  • gently heating ethanol with potassium dichromate(VI) solution and sulphuric acid in a test tube should produce apple smelling ethanal , but you could end up with ethanoic acid

– to get just an aldehyde, you need to get it out of the oxidising solution as soon as it is formed, you can do this by heating excess alcohol with a controlled amount of oxidising agent in distillation apparatus, so aldehyde can be distilled immediately

– to produce the carboxylic acid, the alcohol has to be vigorously oxidised, so heated with excess oxidising agent and under reflux

79
Q

What do tertiary alcohol oxidise to?

A
  • they don’t oxidise
  • you must burn them
80
Q

How can you test whether a compound is an aldehyde or a ketone?

A
  • using benedict’s solution
  • which is a blue solution of copper(II) ions dissolved in sodium carbonate
  • if it’s heated with an aldehyde, the blue copper(II) ions are reduced to a brick-red precipitate of copper (I) oxide
  • if it’s heated with a ketone, nothing happens as ketones cannot be easily oxidised

A Level Chemistry (19 decks)

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