Organic Chemistry



Organic Chemistry Summary 2012/13

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 |First member |Solubility |Solubility in cyclohexane |

| | | |in water [polar] |[non-polar] |

|Alkane |C – C |Methane CH4 [CnH2n+2] |Insoluble |Soluble |

|Alkene |C = C |Ethene C2H4 [CnH2n] |Insoluble |Soluble |

|Alkyne |C ≡ C |Ethyne C2H2 [CnH2n-2] |Insoluble |Soluble |

|Alcohols |R – OH |Methanol CH3OH [CnH2n-1OH] |Short Soluble |Short Insoluble |

|Aldehyde |R – CHO |Methanal HCHO |Short Soluble |Short Insoluble |

|Ketones |R – CO – R’ |Propanone CH3COCH3 |Short Soluble |Short Insoluble |

|Carboxylic Acids |R – COOH |Methanoic acid HCOOH |Short Soluble |Short Insoluble |

|Esters |R – COO – R’ |Methylmethanoate HCOOCH3 |Short Soluble |Short Insoluble |

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

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 |Production |Uses |

|Alkane |Crude petroleum / natural gas /decomposing living matter |Fuel |

|Alkene |C2H5OH = C2H4 + H2O [Al2O3, heat] |Making plastics |

|Alkyne |CaC2 + 2H2O = C2H2 + Ca(OH)2 |Fuel |

|Alcohols |C6H12O6 = 2C2H5OH + 2CO2 [zymase yeast] |Beverage, solvent, fuel |

|Aldehyde |C2H5OH + Cr2O72- + H+ = CH3CHO + Cr3+ + H2O |Making plastics, fuels |

| |Primary Alcohol in excess / remove immediately | |

|Ketones |Propan-2-ol [secondary alcohol] |Solvents |

|Carboxylic Acids |C2H5OH + Cr2O72- + H+ = CH3COOH + Cr3+ + H2O |Condiment, solvent, cellulose acetate, food |

| |Dichromate in / then distil |preservatives |

|Esters |C2H5OH + CH3COOH = CH3COOC2H5 + H2O |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 |Carbons |Use |

|Refinery gas |1 – 4 |Lighter fuel, bottled gas |

|Light gasoline | 5 – 10 |Petrol |

|Naphtha | 7 – 10 |Petrochemical |

|Kerosene |10 – 14 |Jet fuel |

|Gas oil [Diesel] |14 – 19 |Lorries, heating systems |

|Lubricating oil |19 – 35 |Gear oil |

|Fuel Oil |30 – 40 |Heavy furnaces |

|Residue |>35 |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]

Propagation

Cl● + CH4 = CH3● + HCl then Learn same using ethane

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]

Alkenes

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

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Polymerisation

Ethene + ethene = polyethene

Propene + propene = polypropylene

Alkenes raw materials for plastics [chloroethene]

Hydrogenation of vegetable oils to give fats

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

[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

Uses

• Solvent

• Beverage

▪ Beer 4%, Wine 13%, Spirits 40% concentrated by distillation

▪ Methanol used to denature ethanol – make it unfit to drink

▪ Fuel

▪ Spirit or Tilley lamp

▪ Gasohol [80% petrol:20%alcohol]

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

Aldehydes

Functional group – CHO [C=O is polar]

3 C2H5OH + Cr2O72- + 8 H+ = 3 CH3CHO + 2 Cr3+ + 7 H2O

* 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 Cr2O72-

* As 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.

* 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

• 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

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

• 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

• Pentylethanoate smells of pears/bananas

• Reaction is esterification or condensation

Soap

• 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

• Soap lathers with deionised [soft] water / forms scum [calcium stearate] with hard water

[pic]

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]

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)

Organic Synthesis

Working out reaction schemes of up to three conversions, recalling familiar reactions

Synthesis involves breaking then making bonds

Greenhouse Effect

• Sun produces long and short wave radiation

• Long bounce off

• Short passes through

• Radiation absorbed by soil and plants

• Released again as long wave

• Trapped in atmosphere

• Energy rises – temperature rises

• Essential for life on earth - problem is enhanced greenhouse effect

• More violent weather, raised sea levels etc.

• CO2 from burning Fossil Fuels and CH4 from rotting vegetation and ruminants are main causes.

Need to know 2 examples e.g. Aspirin, Paracetamol (structures not needed)

Organic Natural Products

Extraction of Clove Oil

• If the level of the boiling water in the steam generator falls too low, the system will not work smoothly. Refill with hot water. Reconnect everything and heat again.

• 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

• 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 adsorbent 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,

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

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).

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Glycerol

Sodium Stearate

Glyceryl Stearate

Glycerol

Sodium Stearate

Glyceryl Stearate

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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 with a little warm water (about 5 cm3).

• Use anti-bumping granules in the steam generator.

[pic]

H-Cl and Cl – Cl

H – OH also required

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Aluminium oxide

Glass wool and ethanol

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

[pic]

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