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chemistry > Topic 6 - Organic Chem I > Flashcards

Topic 6 - Organic Chem I Flashcards

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1
Q

What is the IUPAC ?

A

system for naming organic compounds

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2
Q

What is the process in naming an organic compound ?

A
  1. find stem - longest carbon chain with most side-chains
  2. add functional group
  3. put any side-chains as a prefix in alphabetical order with the number of the carbon it is bonded to
  4. multiple identical side-chains or functional groups use di-,tri- or tetra- (ignore when putting in alphabetical oder)
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3
Q

what is homologous series

A

several organic compounds that have the same functional group and general formula

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4
Q

what is an addition reaction

A

joining two or more molecules together to form a larger molecule

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5
Q

what is a polymerisation reaction

A

joining together lots of simple molecules to form a giant molecule

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6
Q

what is an elimination reaction

A

when a small group of atoms breaks away from a larger molecule

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7
Q

what is a substitution reaction

A

when one species is replaced by another

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8
Q

what is a hydrolysis reaction

A

splitting a molecule into two new molecules by adding H⁺ and OH⁻ derived from water

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9
Q

what is an oxidation reaction

A

when a species loses electrons

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10
Q

what is a reduction reaction

A

when a species gains electrons

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11
Q

what do curly arrows show in a mechanism

A

to show how electron pairs moves around when bonds are made or broken

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12
Q

what is radical substitution mechanism

A

radical substitution of halogens in alkanes to make halogenoalkanes

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13
Q

what is electrophilic addition mechanism

A

addition of halogens and hydrogen halides to alkenes to make halogenoalkanes

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14
Q

what is nucleophilic substitution mechanism

A

nucleophilic substitution of primary halogenoalkanes with aqueous potassium hydroxide to make alcohols and with ammonia to make amines

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15
Q

what are nucleophiles

A

electron pair donors (negatively charged ions/species with lone pair)

electron rich - attracted to electron poor places

attracted to Cδ+ atom (replaces the halogen)

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16
Q

what are electrophiles

A

electron pair acceptors (positively charged ions/species)

electron poor - attracted to electron rich areas

Hδ+ attracted to C=C bond (electron rich)

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17
Q

what are radicals

A

have an unpaired electron

very very reactive

react with anything (+ve, -ve or neutral)

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18
Q

what are isomers

A

two molecules with the same molecular formula but different atomic arrangement

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19
Q

what are structural isomers

A

different structural arrangement of atoms

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20
Q

what are the 3 types of structural isomer and explain

A
  1. chain isomer
    - where the carbon skeleton arranged differently
    - similar chem properties
    - dif physical properties
  2. positional isomer
    - skeleton/functional group same but functional group attached to dif carbon
    - dif physical properties
    - possibly dif chem properties
  3. functional group isomers
    - same atoms arranged into different functional groups
    - very dif physical properties
    - very dif chem properties
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21
Q

Why might it be tricky to spot a structural isomer

A

atoms rotate as much as they like around C-C bonds

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22
Q

What is bond fission

A

breaking a covalent bond

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23
Q

what are the 2 types of bond fission

A

homolytic fission

heterolytic fission

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24
Q

what is heterolytic fission

A

the bonds break unevenly with one of the bonded atoms receiving both electrons from the bonded pair
two dif substances can be formed (eg. cation and anion)

X↷Y →X⁺ + Y⁻

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25
Q

what is homolytic fission

A

bond breaks evenly and each bonding atom receives one electron from bonded pair
two ‘radicals’ formed

X-Y →X● + Y●

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26
Q

what are photochemical reactions

A

reactions started by light

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27
Q

What do radical substitution reactions need to start

A

UV light

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28
Q

what are the three stages in a radical substitution reaction

A

initiation
propagation
termination

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29
Q

what is the initiation stage in radical substitution reaction (use example of Cl₂ + CH₄ →CH₃Cl + HCl )

A

where radicals are produced
1. sunlight provides enough energy to break Cl-Cl bond
(photodissociation)
2. bond splits equally (homolytic fission) 2Cl●

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30
Q

what is the propagation stage in radical substitution reaction (use example of Cl₂ + CH₄ →CH₃Cl + HCl )

A

radicals used up & created
(chain reaction)

  1. chlorine radical attacks methane molecule
    Cl● + CH₄ →CH₃●+ HCl
  2. new methyl radical attacks another chlorine molecule
    CH₃● + Cl₂ →CH₃Cl + Cl●
  3. new chlorine radical can attack another methane molecule and so on until all chlorine and methane has been used up
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31
Q

what is the termination stage in radical substitution reaction (use example of Cl₂ + CH₄ →CH₃Cl + HCl )

A

radicals are destroyed

  1. two free radicals join to make a stable molecule
  2. several possible termination reactions
    eg Cl● + CH₃● →CH₃Cl
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32
Q

What are the 2 problems with radical substitution reactions (use example of Cl₂ + CH₄ →CH₃Cl + HCl )

A
  1. end up with a mixture of products

eg if trying to make chloromethane but there is too much chlorine, dichloromethane, trichloromethane or tertachloromethane can also be produced

  1. can take place at any point on carbon chain - mixture of structural isomers
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33
Q

what is the best way to reduce chance of by-products in a radical substitution reaction (use example of Cl₂ + CH₄ →CH₃Cl + HCl )

A

excess of methane - greater chance for chlorine radical to collide only with methane molecule and not a chloromethane molecule

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34
Q

describe the fractional distillation process of crude oil

A
  1. crude oil vaporised at 350℃
  2. vaporised crude oil goes into fractionating column and raises up through the trays
  3. largest hydrocarbon doesn’t vaporise at all - bp too high = runs at bottom as residue
  4. colder further up column so condenses at dif temperatures
  5. drawn off at dif levels on trays
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35
Q

what are the 3 main methods for obtaining hydrocarbons from crude oil

A

fractional distillation

cracking

reforming

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36
Q

what is the purpose of bubble caps in fractional distillation

A

deflects the rising vapour down into the condensed liquid on the tray

condensed liquid continuously runs off from the tray and would be collected

bubble caps makes the separation more effective.

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37
Q

what is the order to hydrocarbons produced in fractional distillation and their uses (from smallest to largest)

A

gases - camping gas

petrol - petrol (gasoline)

naphtha - processed to make petrochemicals

kerosene (paraffin) - jet fuel, petrochemicals, central heating fuel

gas oil (diesel) - diesel fuel, central heating fuel

mineral oil - lubricating oil

residue (fuel oil) - ships, power stations

residue (wax/grease) - candles, lubrication

residue (bitumen) - roofing, road surfacing

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38
Q

What is cracking

A

when heavier fractions are ‘cracked’ to make smaller molecules

breaks longer-chain into smaller-chain by breaking
C-C bonds

it is a random process = different mixture of products each time

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39
Q

Why is cracking done

A

higher demand of light fractions - less demand of heavier
things in higher demand = more valuable

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40
Q

what are the two types of cracking

A

thermal and catalytic

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41
Q

what is thermal cracking

A

produces lots of alkenes

high temperatures (up to 1000℃) and high pressures (up to 70 atm)

used to make valuable products eg polymers (plastics)

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42
Q

what is catalytic cracking

A

produces lots of aromatic compounds (those that contain benzene rings) and motor fuels

uses a zeolite catalyst (hydrated aluminosilicate)

slight pressure and high temp (450℃)

cuts cost

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43
Q

What is reforming

A

turns alkanes into cycloalkanes or aromatic hydrocarbons

converts straight-chain into branched-chain

uses catalyst - platinum stuck on aluminium oxide

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44
Q

Why is reforming done

A

to make comubstion more efficient by reducing the chance of knocking

knocking = alkanes explode of their own accord when the fuel in engine is compressed - straight-chain most like likely (eg petrol/diesel)

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45
Q

what is complete combustion of alkanes

A

only products = carbon dioxide and water

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46
Q

what is incomplete combustion of alkanes

A

not enough oxygen around

products = carbon monoxide, carbon and water

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47
Q

Why is carbon monoxide harmful

A

toxic

CO binds better than O₂ to haemoglobin = bind before O₂ can

less oxygen carried around body = oxygen deprivation

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48
Q

Why are sulfur dioxide and nitrogen oxides harmful

A

leads to acid rain

sulfur dioxide = from burning fossil fuels = dissolves in moisture in air = sulfuric acid

nitrogen oxides = produced from high pressures/temps in car engine (O₂ and N₂ in air react) = when escape to atm dissolves in moisture = nitric acid

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49
Q

why is acid rain harmful

A

destroys environment (veg and trees)

corrodes buildings/statues

kills fish in lakes

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50
Q

What are catalytic converters?

A

sit quietly in car exhaust and remove some pollutants from car emissions

51
Q

How do catalytic converters work

A

have a honeycomb structure covered with platinum or rhodium catalyst

exhaust gases react on surface
1. carbon monoxide reacts with nitrogen oxides to form carbon dioxide and nitrogen
2. unburnt hydrocarbons and remaining carbon monoxide react with oxygen to form carbon dioxide and water vapour

52
Q

what are biofuels

A

fuels made from living matter over a short period of time

53
Q

what is bioethanol

A

ethanol made by fermentation of sugar from crops eg maize

54
Q

what is biodiesel

A

made by refining renewable fats and oils eg vegetable oil

55
Q

what is biogas

A

produced by breakdown of organic waste matter

56
Q

How are biofuels still classed as carbon neutral if they release carbon dioxide when burnt

A

its the same carbon dioxide that was absorbed by the plants when growing

however carbon dioxide still give out while refining and transporting as well as when making the fertilisers/powering agricultural machinery when growing/harvesting

57
Q

What is a set back of biofuel

A

petrol car engines would have to be modified to use fuels with high ethanol concentrations

land used to grow these crops can’t be used for food

58
Q

What type of bond do single covalents make

A

sigma (σ) bonds

59
Q

What is a sigma bond

A

two orbitals (can be 2 s, 1 s and 1 p or 2 p )overlap in a straight line in the space between two atoms
gives the highest possible electron density between two nuclei

60
Q

Why is a sigma bond the strongest type of covalent bond

A

the high electron density between the two nuclei means there is a strong electrostatic attraction - high bond enthalpy

61
Q

what type of bond do double covalent bonds make

A

sigma (σ) bond and a pi (π) bonds

62
Q

What is a pi bond

A

two orbitals overlap sideways
‘above’ and ‘below’ molecular axis
(p orbitals)

63
Q

why do pi bonds have a relatively low bond enthalpy

A

the electron density is spread out above and below nuclei
therefore electrostatic attraction is weaker

64
Q

Why cant atoms in C=C bond not rotate around it ?

A

because of the way the p-orbitals overlap to form a pi bond

65
Q

What are stereoisomerisms

A

have the same structural formula but different arrangement

66
Q

What are two types of stereoisomerism

A

Z-isomer
E-isomer

67
Q

What is a Z-isomer

A

‘zusammen’ = together

both above/below double bond and bonded to different carbon

68
Q

What is an E-isomer

A

‘entgegn’ = opposite

one above, one below double bond and bonded to different carbon

69
Q

How does the E/Z system work even when all the groups are different in an alkene ?

A

atom with higher atomic number takes higher priority from each carbon

70
Q

What are the conditions for the electrophilic addition reaction of ethene and hydrogen

A

nickel catalyst

150℃

71
Q

How is margarine made

A

by ‘hydrogenating’ unsaturated vegetable oils

removing double bonds raises melting point of oil - solid at room temp

72
Q

How do halogens react with alkenes to for dihalogenoalkanes (use example of bromine and ethene)

A
  1. double bond repels electrons in Br₂ - polarising it
  2. heterolytic fission (uneven) of Br₂ - the closer Br gives up bonding electrons to other Br and bonds to the C atom
    (curly arrow from bond to atom)
  3. creates carbocation intermediate
    (curly arrow from Br electrons to +ve carbocation)
  4. Br⁻ bonds to second carbon atom
73
Q

What is a test for the presence of C=C bonds ?

A

add brown bromine water
shake
decolourises

74
Q

How can alcohols be made from alkenes ?

A

through steam hydration
300℃ 60-70atm
solid phosphoric acid catalyst

eg. manufacture ethanol from ethene

75
Q

How are alkenes oxidised to create a diol ?

A

shake alkene with acidified potassium manganate, purple solution becomes decolourised

diol is made (2 -OH groups)

76
Q

What happens when a hydrogen halide is added to an unsymmetrical alkene

A

two products are formed

77
Q

In an electrophilic addition reaction of hydrogen halides to an unsymmetrical alkene, what affects the amount of product ?

A

how stable the carbocation is

78
Q

What carbocations are most stable

A

ones with more alkyl groups because they feed electrons to +ve charge

79
Q

How does a hydrogen halide react with an alkene (use hydrogen bromide and propene as an example)

A
  1. partial +ve hydrogen attracted to double bond
  2. electrons in double bond polarise H-Br (repulsion)
  3. heterolytic fission (H+ bonds to one of C)
  4. Br with lone pair bonds to other C

major product =
2-bromopropane as more alkyl groups (more likely)

minor product =
1-bromopropane as less alkyl groups (less likely)

80
Q

What is Markownikoff’s rule

A

the major product from an addition of a hydrogen halide to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrogens already attached

81
Q

What is addition polymerisation

A

when the double bonds in alkenes open up and join together to make long chains of monomers

82
Q

How do you draw the repeat unit in a polymer

A

brackets around repeat unit
double bond = broken to draw as ‘side-links’ through the brackets
write an ‘n’ bottom right corner of bracket

83
Q

What are the 3 methods of disposing of polymers

A

bury
reuse
burn

84
Q

Why can waste plastics be buried ?

A

landfill used when plastic is:
- difficult to separate from other waste
- not in sufficient quantities to make separation financially worthwhile
- too difficult technically to recycle

85
Q

What are the different ways waste plastics can be reused ?

A

plastics like poly(propene) can be recycled by melting and remoulding them

some can be cracked into monomers and then used as organic feedstock to make more plastics or other chemicals

86
Q

What is the purpose of burning waste plastics

A

the heat used to generate electricity

87
Q

Why does the process of burning plastics need to be carefully controlled ?

A

to reduce toxic gases
eg polymers containing chlorine (eg PVC) produce HCl

88
Q

How is the process of burning plastics carefully controlled ?

A

waste gases from combustion passed through scrubbers which neutralise the gases

also plastics can be sorted before burning to separate out any material that will produce toxic gas

89
Q

What principles should chemists follow when they design a sustainable polymer manufacturing process ?

A
  1. use reactant molecules that are as safe and environmentally friendly as possible
  2. use few other materials (solvents) - if so be environmentally friendly
  3. renewable raw material used wherever possible
  4. minimum energy use - catalysts
  5. limit waste products made - especially harmful ones
  6. make sure lifespan of polymer is appropriate for its use
90
Q

What are biodegradable polymers made from

A

renewable raw materials eg starch or from oil fractions

91
Q

What are the advantages of using renewable raw material

A
  • won’t run out like oil
  • when polymers biodegrade CO₂ produced - therefore if plant-based same CO₂ that was absorbed
92
Q

What are the disadvantages to using renewable raw material for biodegradable polymers

A

need right conditions to decompose - need to collect and separate from non-biodegradable
more expensive at the moment

93
Q

What is hydrolysis

A

when water breaks bonds

94
Q

What happens when halogenoalkanes are hydrolysed

A

form alcohols
nucleophilic substitution reaction

95
Q

What haolgenoalkane is hydrolysed the fastest

A

iodoalkanes

96
Q

Explain the nucleophilic subsitution reaction of halogenoalkanes

A
  1. C-halogen bond is polar
  2. +ve carbon accepts electrons from nucleophile
  3. C-halogen bond breaks heterolytically (both electrons taken by halogen)
  4. halogen falls off as nucleophile bonds to carbons
97
Q

What is a way to hydrolyse halogenoalkanes without water (nucleophilic substitution)

A

warm aqueous potassium hydroxide under reflux

(makes alcohol)

98
Q

Why is water slower in the hydrolysis of halogenoalkanes ?

A

its a worse nucleophile than potassium hydroxide

99
Q

What happens when cyanide ions react with halogenoalkanes

A

nitirile and halide ion formed

under reflux
potassium cyanide in ethanol

100
Q

What happens when halogenolakanes react with ammonia

A

amine and ammonium formed

warm halogenoalkane with excess ethanolic ammonia

101
Q

What helps identify an amine

A

smell fishy

102
Q

How can halogenoalkanes undergo elimination reactions

A
  1. halogenalkane mixed with warm alkali (KOH) dissolved in ethanol
  2. heated under reflux
  3. products = alkene, water, eg KBr
103
Q

How can alcohols react to produce chloroalkanes

A

alcohol + PCl₅ or HCl produces chloroalkanes

PCl₅ produces chloroalkane, HCland POCl₃

HCl produces chloroalkane and water

104
Q

How can alcohols react to form bromoalkanes

A

alcohol + bromide ions
produces bromoalkanes
- acid catalyst (50% conc sulfuric acid)

produces bromoalkane and water

105
Q

How can alcohols react to create iodoalkanes

A
  1. alcohol + PI₃
    under reflux with red phosphorous and iodine

produces iodoalkane and H₃PO₃

106
Q

How can alcohols be dehydrated to form alkenes

A
  1. alcohol + acid catalyst (conc phosphoric acid)
  2. heat
  3. water eliminated
107
Q

What colour flame does ethanol make

A

pale blue

108
Q

What can be used to mildly oxidise alcohols

A

acidified dichromate

109
Q

What are primary alcohols oxidised to

A
  1. aldehydes (-al) R-CHO
  2. carboxylic acid R-COOH
110
Q

What are seondary alcohols oxidised to

A

ketones (-anone) R=O=R

111
Q

What are tertiary alcohols oxidised to

A

nothing

112
Q

How to test for a solution is an aldehyde or a ketone

A

benedict’s solution (copper(II) ions dissolved in sodium carbonate)
heated with aldehyde - blue copper(II) ions reduced to brick-red precipitate copper (I) ions

heated with ketone - nothing

113
Q

In oxidation of alcohols, what happens to the oxidising agent acidified dichromate (VI)

A

orange dichromate(VI) reduced to green chromium(III)

114
Q

How to control how far primary alcohols are oxidised

A

to get an aldehyde:
- get out of oxidising solution asap
- heating excess alcohol with controlled amount of oxidising agent in distillation

to get carboxylic acid:
- alcohol oxidised vigorously
- under reflux

115
Q

What is the only way to oxidise tertiary alcohols

A

burning them

116
Q

Why is refluxing used

A
  1. ensure volatile organic substances aren’t lost
  2. organic reactions are slow and flammable and volatile
  3. therefore using bunsen burner = evaporate or catch fire
117
Q

How does reflux work

A
  1. mixture heated in flask fitted with vertical Liebig condenser
  2. continuously boils, evaporates and condenses vapours
  3. recycles them back into flask
  4. gives time to react

note - heating should be electrical = avoid naked flames

118
Q

What is distillation

A

separates substances with different boiling points

119
Q

How does distillation work

A
  1. gently heat mixture in distillation apparatus
  2. thermometer shows boiling pt of substance evaporating
  3. if known bp of pure substance thermometer shows evap and therefore condensing
  4. place flask at open end of condenser to collect product
  5. when temp changing place different flask
120
Q

How does separation work

A
  1. pour mixture into separating funnel, then add water
  2. shake and allow to settle
  3. organic layer and aqueous layer are immiscible
121
Q

What does separation do

A

removes any water soluble impurities from product

122
Q

How do you remove traces of water from a mixture

A
  1. add anhydrous salt (eg magnesium sulfate or calcium chloride)
  2. used as drying agent - binds to water to become hydrated
  3. when first added = organic layer is lumpy
  4. add more until all water removed (swirl to look like snow globe)
  5. filter mixture
123
Q

How to detect impurities

A

boiling point higher than recorded value

chemistry (10 decks)

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