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1
Q

evidence for benzene having a delocalised structure

A
  • bond length intermediate between short c=c and long c-c
  • enthalpy of hydrogenation less exothermic than expected when compared to enthalpy of hydrogenation for kekule structure
  • only reacts with br2 at high temp or in presence of a halogen carrier
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2
Q

compare benzene to alkenes with bromine

A
  • alkenes react easily with bromine at room temp. benzene does not react without halogen carrier
  • in benzene electrons in the pi bond are delocalised, in alkenes they are localised between two carbons
  • benzene therefore has a lower electron density, and polarises br2 less and induces a weaker dipole in bromine
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3
Q

nitration of benzene
- forms?
- reagents
- mechanism
- electrophile
- equation for formation of the electrophile
- overall equation
- mechanism drawing

A
  • nitrobenzene
  • conc nitric acid in the presence of conc sulfuric acid
  • electrophilic substitution
  • NO2+
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4
Q

what is the importance of nitrating benzene

A

useful in
TNT
the formation of arenes

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5
Q

why is nitration of benzene done at 60 degrees

A

at higher temps, a second nitro group can be substituted onto different positions on the ring

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6
Q

halogenation of bromine and chlorine
- forms?
- conditions
- mechanism
- equation for formation of electrophiles
- overall equation
- mechanism drawing

A
  • bromobenzene/chlorobenzene
  • for bromine = febr3
    for chlorine = alcl3
  • electrophilic substitution
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7
Q

benzene alkylation
- forms?
- reagents
- conditions
- mechanism
- equation for formation of electrophiles
- overall equation
- mechanism drawing

A
  • alkylbenzene
  • chloroalkane in the presence of anhydrous aluminum chloride catalyst
  • heat under reflux
  • electrophilic substitution
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8
Q

benzene acylation
- forms?
- reagents
- conditions
- mechanism
- equation for formation of electrophiles
- overall equation
- mechanism drawing

A
  • phenyl ketone
  • acyl chloride in the presence of anhydrous aluminum chloride catalyst
  • heat under reflux (50 degrees)
  • electrophilic substitution
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9
Q

where will substitutions occur when OH or NH2 are present

A

2 and 4 positions on the ring

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10
Q

where will substitutions occur when NO2 is present

A

position 3 on the ring

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11
Q

benzene molecular formula

A

c6h6

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12
Q

benzene
- shape
- bond angle

A

planar
120 degrees

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13
Q

how does a sigma bond form in alkanes

A

one sp3 orbital from each carbon overlap

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14
Q

alkanes
- bond angle and shape

A

tetrahedral as all four bond pairs repel equally
109.5

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15
Q

why does bp increase as alkane size increases

A

number of electrons increases
increase in size of induced dipole dipole interactions

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16
Q

why do branched alkanes have lower bp compared to straight chain alkanes

A

larger surface area of contact in straight chains, therefore stronger induced dipole dipole interactions

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17
Q

why do alkanes have a low reactivity

A
  • high bond enthalpy of the c-c bond and c-h bond
  • low polarity of sigma bonds
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18
Q

what are the economic reasons for cracking.

A
  • fractions with shorter c chains are in more demand
  • to make use of excess larger hydrocarbons and to supply demand for shorter ones
  • the products of cracking are more valuable than the starting materials
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19
Q

conditions for cracking

A

slight pressure
high temp (450 degrees)
zeolite catalyst

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20
Q

condition required for synthesis of chloroalkanes

A

uv light

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21
Q

how are sigma and pi bonds formed in alkenes

A

sigma - two sp2 orbitals overlap
pi - sideways overlap of two p orbitals

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22
Q

alkenes
- angle
- shape

A

120 degrees
planar

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23
Q

what are the effects of e-z stereoisomerism on physical properties

A

e - molecule is non-polar, only contains london forces so bp is lower
z - polar, IMF are london and permanent dipole dipole, so bp is higher

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24
Q

alkenes with hydrogen reaction
- conditions
- type of reaction

A
  • h2 and nickel catalyst
  • addition
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25
Q

alkenes with bromine/chlorine reaction
- reagent
- type of reagent
- conditions
- mechanism
- type of bond fission
- draw the mechanism

A
  • br2
  • electrophile, Br+
  • room temp
  • electrophilic addition
  • heterolytic
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26
Q

alkenes with HBr
- reagent
- type of reagent
- conditions
- mechanism
- draw the mechanism

A
  • HBr
  • electrophile , H+
  • room temp
  • electrophilic addition
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27
Q

alkenes with steam reaction
- what does it form
- reagent
- conditions
- type of reaction

A
  • alcohols
  • steam
  • high temp (300-600)
    high pressure (70atm)
    conc h3po4
  • hydration as water is ADDED
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28
Q

ways to deal with waste polymers

A
  • seperation and recycling
  • feedstock for cracking
  • combustion for energy production
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29
Q

why do alcohols have low volatility

A

due to their ability to form h bonds between alcohol molecules

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30
Q

why are smaller alcohols soluble in water

A

due to their ability to form h bonds with the water

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31
Q

what are the uses of alcohols

A

ethanol - solvent in methylated spirits
methanol - petrol additive to improve combustion, feedstock in production of organic chemicals

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32
Q

partial oxidation of primary alcs
- forms ?
- reagents
- conditions
- observation
- draw equation for oxidation of propan-1-ol to propanal

A
  • aldehyde
  • potassium dichromate and dilute sulfuric acid
  • heat and gently distil
  • orange dichromate ion reduces to the green Cr3+ ion
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33
Q

what colour does k2cr207 go during oxidation

A

orange turns green

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34
Q

full oxidation of primary alcs
- forms?
- reagents
- conditions
- draw equation for oxidation of propan-1-ol to propanoic acid

A
  • carboxylic acid
  • potassium dichromate and dilute sulfuric acid
  • heat under reflux
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35
Q

oxidation of secondary alcs
- forms?
- reagents
- conditionsdraw equation for oxidation of propan-2-ol to propanone

A
  • ketone
  • potassium dichromate and dilute sulfuric acid
  • reflux
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36
Q

reaction of alcs with dehydrating agents
- forms?
- reagents
- type of reaction

A
  • alkene and water
  • conc sulfuric acid or phosophoric acid
  • heat under reflux
  • elimination reaction
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37
Q

substitution reaction of alcohols
- forms?
- reagents

A
  • haloalkane
  • conc sulfuric and sodium halide
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38
Q

nucleophilic substitution of haloalkanes
- forms?
- reagent
- conditions
- mechanism
- draw the mechanism

A
  • alcohol
  • potassium hydroxide
  • in aq solution, heat under reflux
  • nucleophilic substitution
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39
Q

why are smaller carbonyls soluble in water

A

they can form H bonds with water

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40
Q

oxidation of aldehydes
- forms?
- reagent
- conditions
- observation
- equation

A

carboxylic acid
potassium dichromate and dilute sulfuric acid
heat under reflux
orange dichromate ion reduces to the green cr3+ ion

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41
Q

tollens reagent
- made of?
- conditions
- reaction
- observation
- equation

A
  • aqueous ammonia and silver nitrate
  • heat gently
  • aldehydes are oxidised into a carboxylic acid. silver(I) ions are reduced to silver atoms
  • silver mirror forms coating the inside of the test tube
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42
Q

reduction of carbonyls
- reagents
- conditions
- what do aldehydes form when reduced
- what do ketones form when reduced
- draw mechanism
- type of mechanism

A

NaBH4 in aq ethanol
room temp and pressure
primary alcohols
secondary alcohols
nucleophilic addition

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43
Q

catalytic hydrogenation
- type of reaction
- reagent
- conditions

A
  • reduction
  • h2 and nickel catalyst
  • high pressure
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44
Q

formation of hydroxynitriles
- reagent
- conditions
- mechanism
- why don’t we use HCN
- draw mechanism

A
  • NaCN and dilute H2SO4
  • room temp and pressure
  • nucleophilic addition
  • toxic gas that is difficult to contain
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45
Q

reaction with 2.4 DNP
- what does it react with
- observation
- how to identify which carbonyl was used

A
  • aldehydes and ketones
  • orange precipitate
  • take the melting point of the orange crystals, and compare with known values in the database
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46
Q

name of the process by which a chlorine molecule splits into two free radicals

A

homolytic fission

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47
Q

free radical definition

A

a reactive species that possesses an unpaired electron

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48
Q

write mechanism for free radical substitution of Br2 and propane

A
49
Q

why are pi bonds vulnerable to attack in alkenes

A
  • exposed and have high electron density
50
Q

when does e z stereoisomerism arise

A
  • when there is restricted rotation around the double bond
  • when there are two different groups attached to both ends of the double bond
51
Q

why are alkenes reactive

A

due to relatively low bond enthalpy of the pi bond

52
Q

why do alkenes undergo addition reactions

A
  • the double bonds are areas with high electron density - this attracts electrophiles and therefore they undergo addition reactions
53
Q

what is markonwikoffs rule

A

in most cases, the bromine eg will attach to the carbon with the fewest hydrogens on it

54
Q

what is the order of stability for carbocations and why

A

tertiary > secondary > primary
- because methyl groups on either side of the positive carbon are electron releasing and reduce the charge on the ion and stabilise it

55
Q

draw the addition polymer of ethene
- explain why poly(alkenes) are unreactive

A
  • due to the strong C-C and C-H bonds
56
Q

what are the industrial importances of alkenes

A
  • formation of polymers from ethene based monomers
  • manufacture of margarine by catalytic hydrogenation of unsaturated veg oils using hydrogen and a nickel catalyst
57
Q

alcohols general formula

A

CnH2n+1OH

58
Q

how to maximise yield during distillation

A

only collect the distillate at the approximate boiling point and not higher
collection flask can also be cooled in ice

59
Q

why can tertiary alcohols not be oxidised

A
  • no hydrogen atom bonded to the carbon with the OH group
60
Q

equation for the formation of ozone

A

O + O2 →O3 (reversible)

61
Q

destruction of ozone layer by chlorine free radicals equation
destruction of ozone layer by NO equations

A

on chemrevise

62
Q

describe benzenes structure

A
  • 6 carbon atoms in a hexagonal ring with one H bonded to each C atom
  • each C atom is bonded to two other C atoms and one H atom by single covalent sigma bonds
  • this leaves one unused electron on each C atom in a p orbital
  • the six p electrons are delocalised in the ring structure above and below the plane of carbon atoms
63
Q

benzene formula

A

C6H6

64
Q

benzene
- shape
- bond angle

A

planar
120 degrees

65
Q

draw enthalpy of hydrogenation diagram to represent benzene

A

chemrevise

66
Q

phenol reaction with bromine
- reagents
- conditions
- draw overall reaction
- observations

A
  • Br2
  • room temp
  • bromine water decolourises and a white precipitate is formed
67
Q

phenol reaction with nitric acid
- reagent
- conditions
- overall reaction

A
  • 4M HNO3
  • room temp
68
Q

solubility of carboxylic acids in water

A

smaller carboxylic acids (up to C4)dissolve in water but after this solubility decreases. they dissolve as they can form hydrogen bonds with the water molecules

69
Q

test for carboxylic acids

A

add sodium carbonate and there is effervescence

70
Q

why do aliphatic amines act as a base
why don’t aromatic amines act as a base

A
  • lone pair of electrons on the nitrogen is readily available for forming a dative covalent bond with a H+ and so accepts a proton
  • don’t form basic solutions as the lone pair of electrons on the nitrogen delocalise with the ring of electrons in he benzene ring, therefore N is able to accept less protons
71
Q

amines + acids
- form?
- how to convert back into an amine?

A

ammonium salts
add NaOH to the ammonium salt to convert back to an amine

72
Q

amine + ammonia
- forms?
- reagent
- draw the mechanism

A
  • primary amine
  • excess ammonia is the reagent (this limits further substitution and maximises the amount of primary amine formed
73
Q

how to make secondary and tertiary amines

A

secondary: primary amine + haloalkane
tertiary: secondary amine + haloalkane

74
Q

reducing nitroarenes
- forms?
- reagent
- conditions
- mechanism
- draw equation

A
  • aromatic amine
  • Sn and conc HCL
  • heating under reflux
  • reduction
75
Q

draw the general structure of an alpha amino acid
- why is it called an alpha amino acid?

A
  • both the NH2 and COOH groups are joined to the same carbon
76
Q

explain why the enthalpy of hydrogenation of benzene is lower than expected

A

The delocalisation (of electrons) in the benzene ring increases the stability

77
Q

why is methyl benzene more reactive than benzene

A
  • methyl group is electron donating
  • Making the benzene ring more able to attack electrophiles
78
Q

amines reaction with acids
- forms?
- how to convert back to amine?
- write equation for reaction of butylamine and HCl

A
  • ammonium salts
  • add NaOH
  • CH3CH2CH2CH2NH2 + H20 → CH3CH2+NH3 + OH-
79
Q

draw mechanism for the reaction of a primary amine with excess ammonia dissolved in ethanol and a haloalkane
- why is excess ammonia used
- what other conditions are needed

A
  • to limit further substitution maximising the amount of primary amine formed
  • hot and under pressure
80
Q

what is a tertiary amine

A

an organic molecule with three R groups attached

81
Q

amines can be produced from haloalkanes, explain how a mixture of primary, secondary, tertiary and quaternary amines are produced in these reactions

A

More than one hydrogen on the nitrogen atom from ammonia can be substituted

82
Q

functional group of a primary amide

A

-CONH2

83
Q

general formula of an alpha amino acid

A

RCH(NH2)COOH

84
Q

do condensation or addition polymers decompose better? and why?

A
  • condensation polymers
  • they can be hydrolysed into their component monomers
85
Q

hydrolysis reaction definition

A

the breakdown of a compound in the presence of an aqueous solution

86
Q

describe the reaction conditions and state what happens to the polyester during acid hydrolysis

A

The polyester is heated under reflux in the presence of sulfuric acid
- the polyester breaks down with the acid acting as a catalyst

87
Q

outline the difference in the products between acid and base hydrolysis of a polyester

A

Acid hydrolysis produces a dicarboxylic acid
Base hydrolysis produces the salt of a dicarboxylic acid

88
Q

why are addition polymers less reactive than condensation polymers

A

-only contain single bonds
-non polar so chemically inert
- polyesters contain polar bonds so can react with acids and alkalis

89
Q

what is the product when cyclohexene and bromine react together

A

1,2 dibromocyclohexane

90
Q

Explain the relative resistance to bromination of benzene compared to
phenol and compared to cyclohexene.

A
  • benzene electrons/pi bonds are delocalised
  • phenol: the OH group is partially delocalised into the ring
    -cyclohexene electrons are localised
  • benzene has a lower electron density than phenol or cyclohexane
  • benzene cannot polarise or induce a dipole in Br2
91
Q

how does a halogen carrier allow a reaction to take place

A

induces a permanent dipole

92
Q

Explain the relative resistance to bromination of benzene compared to phenol and compared to cyclohexene

A

greater reactivity of phenol….
(the ring is activated because …)
lone pair from O is delocalised into the ring (1)
so electron density (of the ring) is increased (1)
so electrophiles are more attracted (to the ring)

93
Q

delocalised π-bond electrons definition

A
  • electrons are spread over more than two atoms
  • pi bond formed by overlap of p orbitals
94
Q

why do aldehydes give a different reaction to tollens reagent than ketones

A

aldehydes can be oxidised to a carboxylic acid

95
Q

how does gas chromotography separate substances

A

relative solubility in stationary phase

96
Q

amino acid general formula

A

RCH(NH2)COOH

97
Q

Name the process by which TLC separates α-amino acids

A

adsorption

98
Q

rf value definition

A

Rf value is distance moved by a component/spot/solute divided
by distance moved by solvent

99
Q

retention time definition

A

Retention time is the time between injection and emergence
(or detection) of a component

100
Q

what are the roles of the gas and liquid in chromatography

A

gas: mobile phase
liquid: stationary phase

101
Q

State the physical process on which the separation used in gas-liquid chromatography depends

A

partition

102
Q

recrystallisation method

A
  • dissolve the impure compound in a minimum amount of hot solvent
  • hot filter solution through filter paper
  • cool the filtered solution by inserting beaker in ice
  • suction filtrate with buchner flask to separate out crystals
  • wash crystals with distilled water
  • dry between absorbant paper
103
Q

State and explain the effect of the –OH group on the reactivity of the benzene
ring in phenol.

A
  • lone pair from o atom is delocalised into the ring
  • greater electron density around the ring
  • attracts electrophiles
104
Q

why do optical isomers form

A
  • if there is a chiral carbon
  • mirror images cannot be superimposed
105
Q

what do optical isomers have in common and what varies?

A

similar physical and chemical properties
rotate plane polarised light in different directions

106
Q

what is the isoelectric point

A

the ph at which the overall charge of a molecule is zero

107
Q

why does the C=O double bond aid biodegradability

A

absorbs radiation
ester linkage hydrolysed

108
Q

Explain how the student could analyse the chromatogram to identify the three molecules present

A
  • measure how far each spot travels relative to the solvent front/calculate the rf value
  • compare rf values to those known for the molecules
109
Q

Explain how the gas/liquid chromatogram could be used to determine the
percentage composition of each component in the mixture.

A

measure area under each peak
find total area

110
Q

State what quantitative value is normally used to identify the components in gas liquid chromatography AND State the physical process on which the separation used in gas-liquid
chromatography depends.

A

retention time
partition

111
Q

how to purify an organic liquid

A
  • put the distillate of impure product into a separating funnel
  • wash by adding saturated sodium chloride solution
  • allow the layers to separate in the funnel, and the run and discard the aqueous layer
  • run organic layer into a clean dry conical flask and add drying agent
    -decant liquid into distillation flask
  • distill to collect pure product
112
Q

molecular ion peak meaning
base peak meaning

A
  • the peak caused by the unfragmented molecule
  • peak with the greatest relative intensity
113
Q

what happens when D2O is added to a sample

A
  • can be used to identify N-H and O-H peaks
  • protons bonded to electronegative atoms will be able to hydrogen bond to D2O
  • therefore peak will disappear
114
Q

esterification
- two molecules needed?
- produces?
- reagents

A

alcohol + c acid
ester and water
strong sulfuric acid catalyst

115
Q

hydrolysis of esters

A
  1. with acid
    - HCl dilute and heat under reflux
    - produces c acid and alcohol
  2. with dilute NaOH
    - heat under reflux
    -produces salt and alcohol
116
Q

rate of substitution in the halogens

A
  • iodoalkanes are fastest to substitute
  • fluoroalkanes are slowest
  • the strength of the C-F bond means that they are very unreactive
117
Q

how to compare the rate of hydrolysis reactions in haloalkanes

A
  • aq silver nitrate added
  • forms a silver halide precipitate
  • rate of the formation of the precipitate can be used to compare reactivity of the different haloalkanes
118
Q

reactivity of benzoic acid

A

COOH is an electron withdrawing group
electron density is lower
therefore less susceptible to attack

chem (6 decks)

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