SUMMARY SHOWN HERE MUST BE UP-DATED WHEN
CHAPTER 23 IS FINISHED
Organic Chemistry Summary 2015/16
Tetrahedral Carbon
Only single bonds / tetrahedral / three dimensional / molecules can rotate around single bonds /
allows different shapes
Alkanes, chloroalkanes and alcohols [names and structures up to C4]
Used as fuels and solvents
Planar Carbon
Double or triple bond / two dimensional / can’t rotate around double or triple bond
Alkenes, alkynes etc.
Molecules can have planar part and tetrahedral parts
Hydrocarbon = contains C and H only
Saturated = only has single covalent bonds [alkanes, chloroalkanes]
Test - do not decolourise bromine or acidified KMnO4
Unsaturated = contains at least one double or triple bond [alkenes, alkynes]
Test - decolourise bromine from red or acidified KMnO4 quickly
Homologous Series
 Same General Formula
 Same Functional Group
 Differ by CH2
 Same method of preparation
 [similar physical and chemical properties]
Fractional Distillation separation of liquids using their different boiling points
Name
Functional
group
Alkane
Alkene
Alkyne
Alcohols
Aldehyde
Ketones
Carboxylic Acids
Esters
C–C
C=C
C≡C
R – OH
R – CHO
R – CO – R’
R – COOH
R – COO – R’
First member
Methane CH4 [CnH2n+2]
Ethene C2H4 [CnH2n]
Ethyne C2H2 [CnH2n-2]
Methanol CH3OH [CnH2n-1OH]
Methanal HCHO
Propanone CH3COCH3
Methanoic acid HCOOH
Methylmethanoate HCOOCH3
Solubility
in water
[polar]
Insoluble
Insoluble
Insoluble
Short Soluble
Short Soluble
Short Soluble
Short Soluble
Short Soluble
Solubility controlled by
Polar OH group – leads to hydrogen bonding –
Soluble in polar [water] – insoluble in non-polar [cyclohexane and benzene]
BP and MP higher than expected for Molecular Mass
1
Solubility in
cyclohexane
[non-polar]
Soluble
Soluble
Soluble
Short Insoluble
Short Insoluble
Short Insoluble
Short Insoluble
Short Insoluble
Polar C = O [carbonyl group] – does not lead to hydrogen bonding
Soluble in polar [water] – insoluble in non-polar [cyclohexane and benzene]
BP and MP higher than expected for Molecular Mass
Names and structures up to C4
Production and Uses
Name
Alkane
Alkene
Alkyne
Alcohols
Aldehyde
Ketones
Carboxylic
Acids
Esters
Production
Crude petroleum / natural gas /decomposing living matter
C2H5OH = C2H4 + H2O [Al2O3, heat]
CaC2 + 2H2O = C2H2 + Ca(OH)2
C6H12O6 = 2C2H5OH + 2CO2 [zymase yeast]
C2H5OH + Cr2O72- + H+ = CH3CHO + Cr3+ + H2O
Primary Alcohol in excess / remove immediately
Propan-2-ol [secondary alcohol]
C2H5OH + Cr2O72- + H+ = CH3COOH + Cr3+ + H2O
Dichromate in / then distil
C2H5OH + CH3COOH = CH3COOC2H5 + H2O
excess / reflux
Uses
Fuel
Making plastics
Fuel
Beverage, solvent, fuel
Making plastics, fuels
Solvents
Condiment, solvent, cellulose
acetate, food preservatives
Solvents, flavours
Alkanes
Saturated hydrocarbons
Non-polar so insoluble in water
Sources Crude petroleum / natural gas / decomposing animal and plant matter
Separated by fractional distillation – due to differing boiling points due to different RMMs.
Fraction
Refinery gas
Light gasoline
Naphtha
Kerosene
Gas oil [Diesel]
Lubricating oil
Fuel Oil
Residue
Carbons
1–4
5 – 10
7 – 10
10 – 14
14 – 19
19 – 35
30 – 40
>35
Use
Lighter fuel, bottled gas
Petrol
Petrochemical
Jet fuel
Lorries, heating systems
Gear oil
Heavy furnaces
Tarmac
Combustion
CH4 + 2 O2 = CO2 + 2 H2O + heat
[balanced equations up to butane]
Combustion can be explosive
Mercaptan added to natural gas to make it smell for easy detection of leaks
Alkanes are our main source of energy
Reaction with Chlorine
Free Radical Substitution – Homolytic Fission - test for saturation
Initiation
Cl2 = Cl● + Cl● [UV]
Learn same using ethane
Propagation
2
Cl● + CH4 = CH3● + HCl then
CH3● + Cl2 = CH3Cl + Cl● [Cl● now free to react with another CH4 and keep reaction going]
Termination
Cl● + Cl● = Cl2
CH3● + Cl● = CH3Cl
CH3● + CH3● = C2H6 [ proof of mechanism / + UV speeds up / so does tetra methyl lead]
Isomers – same chemical formula but different structural formulae
Chloroalkanes – used as flame retardants when fully halogenated CCl4 and CFCs.
Petrol
Crude oil - Fossilised remains of marine animals [zooplankton]
Knocking or auto ignition – premature combustion due to heating caused by pressure before
spark
Octane number – measure of resistance to knocking
Heptane = 0 while 2,2,4 trimethylpentane given value of 100
Decent petrol = 98
Factors affecting octane number
 Chain length – short chain better
 Branching – branched better
 Cyclic – cyclic better
 Additives - adding tetraethyl lead, benzene or MTBE
Improving octane number
 Shorten chains – Catalytic cracking
 Branch chains - isomerisation
 Make cyclic – dehydrocyclisation or reforming
 Add oxygenates – MTBE, ethanol
Catalytic Converters
 Reduce pollution, photochemical smog, acid rain
 Convert NOx and unburned hydrocarbons to CO2, H2O and N2
 Catalysts on ceramic honeycomb – Pt, Rd and Pd
 Poisoned by Pb in petrol
 Example of heterogeneous catalyst [reactants and catalyst in different phases]
3
Alkenes
Glass wool
and ethanol
Aluminium
oxide
General Formula CnH2n
Structure and names to C4
Non-polar so insoluble in water
Production
Dehydration of ethanol - Elimination reaction
C2H5OH = C2H4 + H2O
Aluminium oxide [white powder] as catalyst
Glass wool holds ethanol in place
Heat evaporates ethanol
Remove tube before you stop heating to prevent suck back
Combustion
C2H4 + 3 O2 = 2 CO2 + 2 H2O + heat
[balance up to butene]
Combustion can be explosive
Reaction with Bromine [or other Halogen] - decolourises quickly – test for unsaturation
Heterolytic Fission
H-Cl and Cl – Cl
H – OH also required
Proof of mechanism
If this is done in the presence of chloride
ions then some 1-bromo, 2-chloroethane or 2
bromoethanol or 1,2 dibromoethane, will be
formed
Polymerisation
Ethene + ethene = polyethene
Propene + propene = polypropylene
Alkenes raw materials for plastics [chloroethene]
Hydrogenation of vegetable oils to give fats
4
Alkynes
General Formula CnH2n-2
Non-polar so insoluble in water
Production
 CaC2 + 2 H2O = Ca(OH)2 + C2H2
 Grey lumpy solid
 Becomes white powder with more volume
 Very exothermic
 Acidified copper sulphate removes impurities
such a phosphine
 Sickly sweet smell
Combustion
 Yellow smoky or sooty flame
 C2H2 + 2½ O2 = 2 CO2 + H2O
 Very hot flame with excess oxygen
 Oxyacetylene burner – cutting and welding steel
Unsaturated – shown by
Decolourises bromine quickly from red/orange to colourless quickly
Decolourises acidified permanganate from purple to colourless quickly
Uses
Oxyacetylene burner / Making monomers for addition polymerisation
Alcohols
General formula CnH2n+1OH
Structure and names up to C4
Primary C to which OH is attached has 1 other C attached directly to it [form aldehydes]
Secondary C to which OH is attached has 2 other C attached directly to it [form ketones]
Production
Fermentation
C6H12O6 = 2 C2H5OH + 2 CO2 zymase from yeast is catalyst
Chemically
Hydration of ethene
C2H4 + H2O = C2H5OH
Combustion
C2H5OH + 3 O2 = 2 CO2 + 3 H2O + nrg
5
[most organic compounds burn to give CO2 and H2O]
Solubility
Short chain soluble in water due to polar OH - insoluble in cyclohexane
Long chain insoluble in water - soluble in cyclohexane
Boiling and melting points higher than expected for Relative Molecular Mass doe to polar
OH group
Reaction with Na
Na + C2H5OH = C2H5ONa + ½ H2 sodium ethoxide – safe disposal of Na residues
Uses
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Solvent
Beverage
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Beer 4%, Wine 13%, Spirits 40% concentrated by distillation
Methanol used to denature ethanol – make it unfit to drink
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Spirit or Tilley lamp
Gasohol [80% petrol:20%alcohol]
Fuel
Aldehydes
Functional group – CHO
[C=O is polar]
3 C2H5OH + Cr2O72- + 8 H+ = 3 CH3CHO + 2 Cr3+ + 7 H2O
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Use a Primary Alcohol
Make sure alcohol is in excess [or Cr2O72- limiting reactant]
Put dil H2SO4 into the pear shaped flask.
If diluting the acid, add acid to water, mix constantly and cool,
because the acid reacts very exothermically with water.
Add anti-bumping granules.[Stops bumping (large bubbles) which
may damage apparatus by forming lots of small bubbles instead of a few large ones]
Put a mixture of dichromate / ethanol into dropping funnel.
Heat acid to boiling and stop heating
Then add alcohol/dichromate mixture at a rate such that
(i) the acid keeps boiling {exothermic reaction} and
(ii) the rate of addition of the mixture equals the rate of production of ethanal.
Solution of ethanol/dichromate is amber due to dichromate Cr2O72As reaction proceeds it goes green as Cr3+ is formed
Remove the ethanal as soon as it is formed so no chance of it reacting further into a carboxylic acid.
Condense and collect ethanal in ice bath - it is volatile [BP 20.8oC] - ice bath stops it evaporating.
Water in at base and out at top of condenser
Distillate contains small amounts of impurities - water and ethanol boiled over with the ethanal.
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Shake with anhydrous sodium sulphate [Na2SO4] for 10 mins. - filter off hydrated sodium sulphate
Re-distil and collect fraction boiling between 20 and 23oC. This leaves last of the alcohol behind.
Ethanal reduces Fehling’s solution from blue to red precipitate when heated.
Produces silver mirror on clean test tube when heated with Tollen’s Reagent ammoniacal silver
nitrate
Short chain soluble in water due to polar carbonyl group [C=O]
Combustion
CH3CHO + 2½ O2 = 2 CO2 + 2 H2O
Reaction with acidified dichromate – oxidised to carboxylic acid
4 CH3CHO + Cr2O72- + 6 H+ = 4 CH3COOH + 2 Cr3+ + 3 H2O
Reaction with acidified permanganate – oxidised to carboxylic acid
5 CH3CHO + 2 MnO41- + 6 H+ = 5 CH3COOH + 2 Mn2+ + 3 H2O
Uses
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Solvents
Made in body as alcohol is metabolised
Solution of methanal in water is called formalin - preserves biological specimens – Embalming
Benzaldehyde found in almond kernels
Aldehydes are reduced to primary alcohols using H2 with a Ni catalyst
Ketones are reduced to secondary alcohols using H2 with a Ni catalyst
Ketones
Functional group R – CO – R’
Structure and names up to C4
Made from secondary alcohols using dichromate and acid and heat
Reflux for 30 minutes
They do NOT oxidise further to carboxylic acids
Distil off the ketone
Impurities
water – remove using anhydrous sodium sulphate – shake for 10 min – then filter
Alcohol – remove by fractional distillation
State – first 2 [propanone and butanone] are liquids
Short chain soluble in water due to polar carbonyl group
Uses
Solvents – propanone nail varnish remover
7
Carboxylic Acids
 Heat Ethanol with acidified dichromate in reflux apparatus for 30 minutes.
 Make sure that the oxidising agent (Cr2O72-) is in excess.
3 C2H5OH + 2 Cr2O72- + 16 H+ = 3 CH3COOH + 4 Cr3+ + 11 H2O
 Reflux stops volatile components escaping
 Alcohol is converted first to aldehyde and then onto a carboxylic acid.
 Orange dichromate (Cr2O72-) turned (reduced) to green chromium(III)
(Cr3+).
 pH 3-4 because weak acid [only partly dissociates in aqueous solution]
 CH3COOH + H2O = CH3COO- + H3O+
 Turns UI orange/yellow and litmus blue to red
 2CH3COOH+Na2CO3 = 2CH3COONa + CO2 + H2O (sodium
ethanoate)
 Mg + 2 CH3COOH = (CH3COO)2Mg + H2 (magnesium ethanoate)
 NaOH + CH3COOH = CH3COONa + H2O (sodium ethanoate)
 CH3COOH + C2H5OH = CH3COOC2H5 + H2O
 ethyl ethanoate [ester + water]
Conc. sulphuric acid as a catalyst.
 Fruity smell of ester
 Ethanoic acid removed fitting condenser sideways and collecting
distillate. Replace water bath with sand bath. [BP 119oC]
 Impurities water [Remove water using anhydrous Na2SO4.] and ethanol
[and discard fraction boiling at 80 oC].
Uses of carboxylic acids /
Condiment / preservative [propanoic and benzoic acids]/ making esters / cellulose acetate film
Methanoic acid – nettle and ant stings
Esters
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Functional Group R – COO – R’
Structure and names up to C4
Methanol + Ethanoic Acid = Methyl Ethanoate + water
HCOOH + C2H5OH = HCOOC2H5 + H2O
Reflux for 30 min – reaction needs time
Conc. H2SO4 as dehydrating agent to speed up reaction
Fruity smells and flavours
Fats natural tri-esters
Ethyl ethanoate as solvent
Pentyl ethanoate smells of pears/bananas
Reaction is esterification or condensation
8
Soap
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Reaction is called Saponification [alkaline hydrolysis]
Into pear shaped flask pour sunflower oil [or any fat or oil]
Add 3 g of NaOH pellets [caution – very caustic]
Add 30 ml ethanol to dissolve the fat
Add some anti-bumping granules
Boil under reflux for 30 min. as reaction is slow / prevents volatile components escaping
Reflux prevents loss of vapour from the apparatus during boiling
From time to time swirl flask to remove substances [Na salts of fatty acids and un-hydrolysed
fat] stuck to side of flask
Cool and rearrange apparatus for distillation
Distil off most of the ethanol [about 20ml] to make it easier to isolate the soap
Pour contents of flask into concentrated NaCl solution - Brine
Soap does not dissolve in salt solution so it precipitates out [called salting out]
Excess NaOH stays in solution as does glycerol and alcohol
Filter off the soap and wash with salt solution
C3H5(C17H35COO)3 + 3 NaOH = C3H5(OH)3 + 3 C17H35COONa
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Soap lathers with deionised [soft] water / forms scum [calcium stearate] with hard water
Glyceryl Stearate
Sodium Stearate
9
Glycerol
Benzene – Aromatic Hydrocarbons
Aromatic = has benzene ring in structure
Basis of dyestuffs, detergents, herbicides, many pharmaceuticals and indicators such as methyl orange
and phenolphthalein
Many are carcinogenic e.g. benzene in petrol - but not all e.g. aspirin
Structure of benzene, methylbenzene and ethylbenzene
Methylbenzene used as a solvent for non-polar compounds – not carcinogenic
Insoluble in water because non-polar
Does not react like normal saturated compound – delocalised Pi bonds – shown by ring
Reaction Types
You are required to be able to write balanced equations for the reactions, using structural formulas
[Unless otherwise indicated.]
Addition [Ionic Addition – Heterolytic Fission]– Mechanism required
Alkenes with
Chlorine, [Mechanism required]
C2H4 + Cl2 = C2H4Cl2 [1,2 dichloroethane]
Bromine [Mechanism required]
C2H4 + Br2 = C2H4Br2 [1,2 dibromoethane]
Hydrogen chloride, [Mechanism required] C2H4 + HCl = C2H5Cl
[chloroethane]
HCl approaches H first and H attaches first
Hydrogen,
C2H4 + H2 = C2H6 [ethane]
Water
C2H4 + H2O = C2H5OH [ethanol]
Polymerisation
n C2H4 = [C2H4]n [polythene]
Substitution [Homolytic Fission]
Alkanes with halogens, [Mechanism required see page two]
C2H6 + Cl2 = C2H5Cl + HCl [chloroethane + hydrogen chloride]
Esterification [soap - structures required]
10
Glyceryl Stearate
Sodium Stearate
Glycerol
Elimination –
Removal of water or some other small molecule with the formation of a double bond in the
larger molecule e.g. Dehydration of alcohols to produce alkenes
C2H5OH = C2H4 + H2O
(Al2O3 as catalyst)
Redox – involve both oxidation and reduction
Oxidation
Na2Cr2O7 and KMnO4 turning alcohols to aldehydes and ketones and carboxylic acids
Ethanal
Alcohol in excess / remove ethanal as soon as it is formed
Cr2O72- reduced to Cr3+ / orange to green / ethanol oxidised to ethanal
3 C2H5OH +
Cr2O72- + 8 H+ = 3 CH3CHO
+ 2 Cr3+ + 7 H2O
Ethanoic Acid
Dichromate in excess / reflux for 30 minutes
Cr2O72- reduced to Cr3+ / orange to green / ethanol oxidised to ethanal to ethanoic acid
3 C2H5OH + 2 Cr2O72- + 16 H+ = 3 CH3COOH + 4 Cr3+ + 11 H2O
Reduction
Ethanoic acid
CH3COOH = CH3CH2OH + H2O [H2, Ni catalyst and heat]
Ethanal
CH3CHO = C2H5OH + H2O [H2, Ni catalyst, heat] - primary alcohol
Propanone
CH3COCH3 = CH3CH(OH)CH3 + H2O [H2, Ni catalyst, heat] - secondary alcohol
Reaction as Acids – carboxylic acids with Mg, NaOH and Na2CO3
 CH3COOH + H2O = CH3COO- + H3O+ [ weak only dissociates partly]
 Mg + 2 CH3COOH = (CH3COO)2Mg + H2 (magnesium ethanoate)
 NaOH + CH3COOH = CH3COONa + H2O (sodium ethanoate)
 2CH3COOH+Na2CO3 = 2CH3COONa + CO2 + H2O (sodium ethanoate)
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Organic Synthesis
Working out reaction schemes of up to three conversions, recalling familiar reactions
Synthesis involves breaking then making bonds
Polymers
+ HCl
or Cl2
Chloroalkanes
+ Cl2
+ H2
Alkynes
Alkenes
- H2O
CaC2+ 2 H2O =
Al2O3
Dehydration
C2H2 + Ca(OH)2
secondary
+ H2
Alkanes
+ H2O
Alcohols
Cr2O72-, H+, heat, Oxidation
primary
Aldehydes
H2, Ni, heat
Reduction
Cr2O72-, H+, heat
Oxidation
H2, Ni, heat
Reduction
Ketones
+ H2O
hydrolysis
- H2O
dehydration
H2,Ni, heat
Reduction
Cr2O72
H+, heat.
Oxidation
Carboxylic
Acids
Alkaline
hydrolysis
Need to know 2 examples e.g.
Aspirin, Paracetamol (structures not needed)
Soap
Esters
Organic Natural Products
Extraction of Clove Oil
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Have a safety opening to the atmosphere
Steam distillation used because some components of clove oil
have high BP and this temp would damage molecules in the
oil
 Some organic compounds are immiscible with water. Usually
these compounds have a low vapour pressure. After mixing
them with water, however, the mixture will distil when the
sum of the two vapour pressures reaches atmospheric
pressure. It follows, then, that this must happen below the
boiling point of water.
This process is known as steam distillation.
Cover
cloves
a little
warm
water
(about
5 cm3).falls too low, the system will not work
  If the
level
of thewith
boiling
water
in the
steam
generator
Refill withgranules
hot water.
Reconnect
everything and heat again.
 smoothly.
Use anti-bumping
in the
steam generator.
 After 30 minutes disconnect steam generator to avoid suck-back then turn off the heat.
 Collect 40 - 50 cm3 of the pale milky distillate [emulsion]. Note the smell
12
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Oil separated by dissolving in solvent, placing in separating funnel
Collect organic solvent fraction and then evaporate solvent.
Used for flavouring, painkiller
Chromatography and Instrumentation
Thin Layer or Paper Chromatography
Chromatography as a separation technique in which a mobile phase [water + alcohol] carrying a
mixture [of indicators or dyes from fibres] is caused to move in contact with a selectively
absorbent stationary phase [paper]. This separates the components
Gas Chromatography [GC]
More advanced form. Gas is mobile phase
Uses:- Drug tests on athletes; blood alcohol tests.
High Performance Liquid Chromatography
[HPLC]
Liquid mobile phase – under pressure
Uses:- (i) Examining growth-promoters in meat
(ii) Vitamins in foods.
Mass Spectrometry
Separation of ions / moving in magnetic field /
by mass
Aston invented
Stages
Vaporisation,
Ionisation,
Acceleration,
Separation,
Detection,
Display
Uses:- Analysis of (i) gases from a waste dump
(ii) trace organic pollutants in water.
Atomic Absorption Spectrometry
(1) Infra-red Absorption Spectrometry [IR]
A ‘fingerprinting’ technique involving absorption of infra-red radiation
Tells us the chemical groups present by identifying bonds
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Uses:- Identification of organic compounds, e.g. plastics and drugs
(2) Ultraviolet Absorption Spectrometry [UV]
A quantitative technique involving the absorption of ultraviolet light.
Uses:- Quantitative determination of organic compounds (e.g. drug metabolites, plant
pigments).
Exam Questions on Organic Chemistry
1) 2014 Q.2 Q.4 (i), Q.6, Q.8, Q.10 (a)
2) 2013 Q.2 Q.4 (f), Q.6, Q.8
3) 2012 Q.2 Q.6, Q.8, Q.10 (a)
4) 2011 Q.2 Q.4 (i), Q.6, Q.8
5) 2010 Q.2 Q.4 (j), Q.6, Q.9, Q.10 (b)
6) 2009 Q.2 Q.4 (h), (i), Q.6, Q.8,
7) 2008 Q.2 Q.6, Q.9, Q.11
8) 2007 Q.2 Q.4 (b), (g), (i), (j) Q.6, Q.8
9) 2006 Q.2 Q.4 (d), (g), (j), Q.6, Q.9, Q.10 (c)
10) 2005 Q.2 Q. 4 (g), (i)
Q.6
11) 2004 Q.2 Q.6 Q.7
11) 2003 Q.2 Q.4 (h), (j) Q.6 Q.7 (b) Q.9
12) 2002 Q.2 Q.4 (j) 2002 Q.6
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