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Chemistry > 3.3 Organic Chemistry > Flashcards

3.3 Organic Chemistry Flashcards

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1
Q

What is a functional group?

A

Atom or groups of atoms that causes molecules to have similar chemical properties

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2
Q

What is a homologous series?

A

Organic compounds with same functional group and general formula
•increase by CH2

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3
Q

What is a structural isomer?

A

Same molecular formula but different structure e.g chain, position and functional group isomers

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4
Q

What is a position isomer?

A

Different position of same functional group on same carbon skeleton

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5
Q

What is a functional group isomer?

A

Atoms arranged to give different functional groups

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6
Q

What is a stereoisomer?

A

Same structural formula but different spatial arrangements of atoms e.g E/Z

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7
Q

What causes E/Z isomerism?

A

Occurs as a result of restricted rotation about planar C=C
E: opposite sides
Z: zame Zide
Priority given to bigger atomic no.

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8
Q

What is an alkane and what are its physical properties? (*Useful?)

A

Saturated hydrocarbons, CnH2n+2
:
•non-polar
•low b.p (only van der waals)
•insoluble in water (non-polar)
•very unreactive (C-C strong)

•flammable =fuels
•lubricant
•*make other organic molecules

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9
Q

Why does branching decrease boiling points?

A

Surface area of contact is low so the intermolecular forces are weaker

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10
Q

What is petroleum (crude oil) and how can it be separated?

A

•mix of alkanes
fractional distillation:
•heated in fractionating column until vaporised and it will condense as different fractions based on boiling points

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11
Q

What are the fractions of crude oil and their uses?

A

1) gases: LPG
2) petrol
3)naphtha: make petrochemicals
4)kerosene: jet fuel
5) diesel
6)bitumen: road surfacing

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12
Q

What is cracking and why is it needed?

A

•involves breaking C-C bonds in large alkanes to produce shorter alkanes: more volatile, flammable (useful) ££
•makes alkenes
•match supply with demand

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13
Q

What is needed for thermal cracking?

A

•high pressure: 70 atm
•high temperature : 1000K
= high proportion of alkenes (make e.g polymers)

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14
Q

What is needed for catalytic cracking?

A

•slight pressure
•high temperature (450)
•zeolite catalyst
=motor fuels, aromatic HC e.g benzene, branched alkanes

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15
Q

How are alkanes involved in combustion?

A

Act as fuels:
Complete= fully burns is O2 to form CO2 and H2O
Incomplete= limited O2 to form C (soot), CO, H2O

*Shorter alkanes burn with a clean flame
*longer alkanes burn with sootier flame

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16
Q

What pollutants form from internal combustion engines and how can they be removed?

A

•NOx: can react with HC in sunlight to make ground level O3 (photochemical smog) (lung problems) /acid rain
•unburnt HC
•CO

(Removed using catalytic converters=
2NO + 2CO = N2 + 2CO2

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17
Q

Where does SO2 come from and what are its effects?

A

•fossil fuels burnt with sulfur impurities
•makes acid rain that damages trees and corrodes buildings

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18
Q

How can SO2 be removed from power station flue gases?

A

1) CaCO3 or CaO mix with water=slurry
2)flue gas+slurry=calcium sulfite forms

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19
Q

What is a free radical?

A

Atom or molecule with an unpaired electron, making it very reactive

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20
Q

Give the steps in the free radical substitution of CH4 + Cl2

A

Initiation:
Cl2= 2Cl• (u.v needed)

Propagation:
1) •Cl + CH4= •CH3 + HCl
2) •CH3 +Cl2= CH3Cl + •Cl

Termination:
•CH3 + •CH3= CH3CH3
•Cl + •CH3= CH3Cl

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21
Q

What is homolytic fission?

A

Pair of e- is split between separated atoms

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22
Q

What is heterolytic fission?

A

Pair of e- is taken by one of the atoms

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23
Q

Why does the depletion of the ozone layer occur?

A

u.v causes C-Cl bond in CFCs to break which forms •Cl (homolytic fission so 2 free radicals form)

Propagation:
1) •Cl + O3= O2 + ClO•
2) ClO• + O3= 2O2 + Cl•

Overall 2O3=3O2

So O3 can no longer block u.v light

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24
Q

What is a halogenoalkane and why are they useful?

A

Halogen takes place of H atom in alkane where RCH2-X forms where C-X is a polar bond (more reactive)

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25
Q

What is the R in a halogenoalkane?

A

Alkyl group

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26
Q

What are the different types of halogenoalkanes?

A

•primary: 1 R (alkyl groups)
•secondary: 2 R
•tertiary: 3 R

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27
Q

What does the reactivity of a halogenoalkane depend on?

A

How easy it is to break C-X bond:
•strength of polarity (electronegativity)
•bond enthalpy: which decreases down group 7 so easier to break down

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28
Q

What is a nucleophile?

A

Lone pair donor which forms a bond with something e- deficient

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29
Q

What are the steps in nucleophilic substitution with OH- and CN-?

A
  1. Nucelophile attracted to e- deficient C+ atom in C-X
    2.nucleophile uses its lone pair to form new bond with C+ and C-X bond breaks heterolytically
  2. X gets both e- in the bond, forming a halide ion
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30
Q

What are the conditions/products for the nucleophilic substitutions of OH and CN?

A

OH: warm halogenoalkane with (aq) KOH or NaOH solvent (makes alcohol)
CN:warm halogenoalkane with KCN dissolved in ethanol (not water as OH introduce)
(Makes nitriles, C chain extended so used in organic synthesis)

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31
Q

What is needed for the nucleophilic substitution with ammonia?

A

•excess conc. NH3 solution
1st NH3 acts as a nucleophile, donates lone pair to C+
2nd NH3 acts as a base, donates lone pair to H

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32
Q

What is an elimination reaction?

A

•KOH (dissolved in ethanol)
•heated
OH used as a base (removes H+)

Forms alkene, water and halide ion

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33
Q

What conditions favour nucleophilic substitution?

A

•solvent (aq)
•low temperature
•primary halogenoalkane

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34
Q

What conditions favour elimination?

A

•alcohol or ethanolic solvent
•high temperature
•tertiary halogenoalkanes

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35
Q

What is steric hindrance?

A

:OH- finds it easier to pull off a H atom and act as a base

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36
Q

What is an electrophile?

A

Lone pair acceptor that will attack the high e- density in C=C

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37
Q

How does HBr and Br2 undergo electrophilic addition with an alkene?

A

•H-Br polar as different electronegativity
•Br-Br is polarised by C=C repelling e- and inducing a dipole

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38
Q

Why do major and minor products form?

A

•major product= more alkyl groups (more stable)
•minor products= less alkyl groups
(Less stable)

(More energy is needed to make less stable intermediate carbocation with less alkyl groups)

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39
Q

What is the positive induction theory?

A

Alkyl groups are e- releasing so more alkyl groups, the more stable as they stabilise the carbocation

40
Q

What are the different carbocations?

A

•tertiary: 3 Rs
•secondary: 2 Rs
•primary: 1 R

R: alkyl groups

41
Q

What does the electrophilic addition with concentrated Sulfuric acid produce? (+what needed)

A

•Alcohol when warmed with water
•H2SO4 is regenerated

42
Q

What is a high density Polyethene?

A

•made at room temp/atm
•litter branching= closer + rigid
•makes buckets and bowls

43
Q

What is low density polyethene?

A

•made with high temp./atm
•made by free radical mechanisms
•lots of branching
•non-biodegradable= C-C strong and non-polar
•makes bags

44
Q

What are plasticisers used for?

A

Makes plastics (PVC) more flexible as they can slide over each other

45
Q

What is the elimination of alcohols ?

A

Dehydration to make an alkene
•H+ protonates alcohol (OH)
•positive intermediate is unstable (+H20)
•water eliminated and H+ catalyst is regenerated as C=C made

46
Q

How are alcohols (ethanol) made by hydration? (+conditions/negtaive?)

A

1) hydrate alkane (ethene) using steam and acid catalyst
2) 300•C /60atm /phosphoric (V) catalyst
3)ethene comes from crude oil

47
Q

How is ethanol made form fermentation? (+Conditions/negatives?)

A

•yeast anaerobically respires glucose to make ethanol, purified by fractional distillation (time+££)
•No O2
•40•C

48
Q

What is a biofuel?

A

•Fuel made from biological material that has recently died
•carbon neutral as no net emission of CO2

49
Q

What are the ethical issues of biofuels?

A

•transport: petrol car engines have to be modified
•land not used to grow food= food scarcity

50
Q

Why is burning ethanol from fermentation carbon neutral (equations)? (+Why is it not?)

A

Photosynthesis:
6CO2 + 6H2O= C6H12O6 + 6O2
Fermentation:
C6H12O6= 2C2H5OH + 2CO2
Combustion:
2C2H2OH= 4CO2 + 6H2O

6 moles of CO2 taken in and 6 moles out (no net CO2 emission)

•fossil fuels burnt for fertilisers, harvesting crops, refining and transporting biofuels = + CO2 out

51
Q

What happens in the oxidation of a primary alcohol?

A

• 1• is acidified with potassium dichromate (oxidising agent= (O))
•1st oxidised to aldehydes by distillation
•further oxidised to Carboxylic acids, it is heated under reflux (high temp. without losing volatile solvents)

52
Q

What happens in the oxidation of a secondary alcohol?

A

Oxidised to ketones with acidified potassium dichromate (K2Cr2O7) under reflux

53
Q

What happens to the potassium dichromate in an oxidisation reaction of an alcohol?

A

Orange K2Cr2O7 will turn to green as it is reduced to Cu2+

54
Q

How can you distinguish between alcohols?

A

1• oxidised to adehydes = green
2• oxidised to ketones = green
3• remains orange in acidified K2Cr2O7

Fehling’s solution: blue to brick red ppt if aldehyde only

Tollen’s reagent: silver mirror if aldehyde only

55
Q

How can you tell that a tertiary alcohol cannot be oxidised?

A

Potassium dichromate solution remains orange

56
Q

How do you distinguish between an alkene and alkane?

A

Alkene = decolourise bromine water
Alkane= bromine water stays orange

57
Q

How are Carboxylic acids tested for?

A

•add sodium carbonate and it forms CO2 + fizzes
•bubble gas in limewater = cloudy

58
Q

What is an optical isomer?

A

•Chirac centre = c with 4 different groups attached
•enantiomers= non-superimposable mirror images

59
Q

How do you distinguish 2 enantiomers?

A

Plane polarised light can be shot and it will move in opposite directions

60
Q

What is a racemic mixture?

A

50% of each enantiomer which will rotate plane polarised light in equal and opposite directions to cancel out the charges

61
Q

How does a racemic mixture form?

A

•C=O bond is planar and can be attacked equally from either side by a nucleophile (nucleophilic addition) forming equal amounts of each enantiomers

•carbocation carbon is planar so nucleophile can attack equally from either sides (electrophilic substitution in alkenes)

62
Q

What tests distinguish between ketones and aldehydes?

A

Tollen’s reagent = silver mirror with aldehyde
Fehling’s solution = blue to red ppt. in aldehyde
(No visible changes with ketone)

63
Q

What are aldehydes and ketones reduced to and what reagents/conditions are needed?

A

•aldehyde to 1• alcohol
•ketone to 2• alcohol
Reducing agent of NaBH4 = hydride ion for nucleophilic addition

64
Q

What is formed in the nucleophilic addition of a carbonyl with :CN-?

A

Hydroxynitrile

65
Q

How are esters formed and how are they named?

A

Alcohol + Carboxylic acid undergo condensation reaction (esterification) using H2SO4 catalyst
1. Alkyl (alcohol)
2. -anoate (Carboxylic acid)

66
Q

What are the reagents/conditions needed for the hydrolysis of esters?

A

•Dilute HCl and heat it under reflux
•saponification= (not reversible)
>add excess dilute NaOH to form carboxylate salt (RCOO-Na+) and heat under reflux

67
Q

What are common uses of esters?

A

1.solvents= polar
2.plasticisers
3.perfumes/flavouring= good smell and non-toxic

68
Q

How is soap formed from esters?

A

Fats are added to NaOH which forms glycerol and sodium salt (RCOO-Na+)

69
Q

How is biodiesel formed from esters?

A

Oils react with methanol and KOH catalyst to form glycerol and methyl esters

70
Q

What are acyl chlorides?

A

•Functional group -COCl (Carboxylic acid derivative)
•-oyl chloride

71
Q

What are acid anhydrides and how is it better than using acyl chlorides?

A

•2 Carboxylic acids joined together
• -anhydride e.g ethanoicanhydride

•safer as misty fumes of HCl are not formed = toxic
•less vigorous
•cheaper

72
Q

What is used to filter a solution?

A

A Büchner funnel where it is filtered under reduced pressure

73
Q

What are steps of recrystallisation?

A

1.add minimum amount of hot solvent to dissolve the solid
2.cools = crystals
3.filter to get purified solid crystals and wash with very cold solvent and dry

74
Q

How is purity of a solid sample tested?

A

•put sample in a capillary tube
•place in apparatus and find range at which it starts to melt to it fully melting
•sharp range = pure

75
Q

What is the bonding and shape in a benzene ring?

A

C6H6
•each carbon has 3 covalent bonds with spare e- that overlap which causes delocalisation
•planar and hexagonal
•120• bond angle
•C-C bonds are of equal length

76
Q

Why is benzene more stable than kekule’s model? (+use hydrogenation data)

A

Benzene has a ring of delocalised electrons
•benzene = -208 kJmol-1
•kekule = 3 X -120 = -360 kJmol-1
•hydrogenation benzene enthalpy change is less exothermic by 152 so is more stable = lower in energy

77
Q

How has kekule’s model been disproved for benzene?

A

•C=C is shorter than C-C but in benzene all bonds are equal
•benzene doesn’t undergo electrophilic addition
•benzene is more stable

78
Q

What are the equations for nitration (electrophilic substitution)?

A

conc. HNO3 + conc. 2H2SO4
= +NO2 + 2HSO4- + H3O+

+NO2 is used as an electrophilic (lone pair acceptor)

79
Q

What are the equations for Friedel-Crafts acylation (electrophilic substitution)?

A

RCOCl + AlCl3 = AlCl4- + RCO+
H+ + AlCl4- = AlCl3 + HCl
(AlCl3 is reformed so is a catalyst)

80
Q

Why is TMS used and advantages?

A

•added to calibrate the NMR equipment
•it provides a peak at exactly 0 ppm which is in an area away from other typical H signals
•it is the reference point against at which all are measured
Ad:
•inert
•non-toxic
•easy to remove from the sample (as volatile)

81
Q

When does splitting (spin-spin coupling) occur?

A

Neighbouring H atoms affect the magnetic field of H1 atoms and cause peaks to split

82
Q

What is the n+1 rule?

A

If there are n in equivalent H1 atoms on the neighbouring carbon then the peak will split into (n+1) smaller peaks

83
Q

Which solvents are used and why?

A

CDCl3 and CCl4 are inert solvents that don’t react with sample nor interfere with spectra as they contain no H

CCL4= non-polar solvent, ideal for H1 NMR of non-polar molecules
CDCl= polar solvent, ideal for H1 NMR of polar molecules

84
Q

How can amines form from halogenoalkanes and how can it form a primary amine?

A

Nucleophilic substitution with ammonia

Use excess ammonia if you want to form only 1• amine

85
Q

Explain amines being bases

A

Bases= proton acceptors
•strongest base had the greatest e- density around the N atom = primary amine where inductive effect pushes the e- so the lone pair is more available
•NH3
•aromatic amines = less available as the lone pair has become delocalised into the benzene ring

86
Q

What effect do aryl groups have on base strength?

A

Negative inductive effect = decrease e- density around N = weaker base

87
Q

Why are 3• amines not good bases?

A

They are insoluble in water

88
Q

How is a nitrile form?

A

Nucleophilic sub with a halogenoalkane and :CN- (ethanol as solvent)

89
Q

How do you form a 1• amine from nitriles?

A

Reduction using nickel/ hydrogens catalysts
(More pure as only 1• amines form)

90
Q

How is an ammonium chloride salt formed from nitrobenzene?

A

Reduce nitrile using tin/HCl to from an ammonium salt with Cl- ions at room temp.
Add excess NaOH to form phenylamine

91
Q

What is the equation for the reaction of nitrobenzene to phenylamine?

A

C6H5NO2 + 6[H]= C6H5NH2 + 2H2O

92
Q

What are cationic surfactants?

A

4• ammonium salts,
The HC tail binds to the non-polar substances and the cationic head dissolves in water

93
Q

What is an arene?

A

HC containing one or more benzene rings

94
Q

What steps are taken during recrystallisation and why?

A

•minimum hot water = ensure hot solution would be saturated/crystals form on cooling
•cool before filtering= yield is lower of warm as solubility is higher
•crystals compressed in funnel=air passes through sample not just sound it
•a little cold water poured through crystals=to wash away soluble impurities

95
Q

What causes crystals formed during recrystallisation to have a lower m.p than expected?

A

Water impurities. Improved reading by pressing the sample of crystals between filter papers

Chemistry (3 decks)

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