Organic Chemistry

Organic Chemistry


Organic Chemistry - Basics

Functional Group -  Atoms that give the compound it's characteristics

Homologous Series - Same functional group different length hydrocarbon chain, examples; Alcohols, Alkanes, Alkenes, Halogenoalkanes, Aldehydes, Ketones, Carboxylic acid, Esters.

Saturated hydrocarbons - compounds that  contain only carbon and hydrogen and have single covalent bonds, general formula: CnH2n+2

Structural Isomers: same molecular formula but different structural formula

Chain isomers: skeletal formulae are different branched in different ways

Positional isomers: functional group attached to a different carbon atom

Stereoisomers/EZ isomerism: same molecular formula but different arrangement in space.  E=trans  /  Z=cis

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Converting Alkanes

Fractional distillation: separation by boiling point. 

 Fractionating column, larger hydrocarbon chains run to residue at the bottom as their boiling points are too high to be vapourised. These end up as fuels and petrochemicals. Kerosene - Aeroplane fuel.

Cracking (Ceramic: breaking long chain alkanes into smaller alkanes

Catalytic cracking cuts costs producing large amounts of branched hydrocarbons useful for making petrol

Isomerisation(Platinum with inert aluminium oxide): changing straight-chain alkanes to branched-chain alkanes 


Reforming(Platinum): changes straight-chain alkanes to cyclic alkanes

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Oxidising alkanes by combustion:

CH4(g)+2O2(g) → CO2(g)+2H2O(g) - Complete Combustion

Smaller molecules are more volatile so they burn more easily, but larger molecules are more exothermic as more bonds broken. Alkanes are good fuels; propane for central heating/cooking, butane for camping gas.

CH4(g)+1.5O2(g) → CO(g)+2H2O(g) - Incomplete Combustion

In a lack of oxygen carbon monoxide is formed instead of carbon dioxide. CO is extremely poisonous, they bind with the haemoglobin in the red blood cells better than oxygen. This will lead to oxygen deprivation thus headaches and nausea.

 Percentage Yield: Actual over Theoretical x100

Atom economy: Mr of useful product/sum Mr of all products

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Electrophilic Addition

Heterolytic bond fission: breaking covalent bond to form 2 different substances

Homolytic bond fission: breaking covalent bond to form 2 free radicals

Electrophilic addition of alkenes (Nickel Catalyst / 150℃)


C2H4 + H2 → C2H6 - 

Margerine(S) is made by hydrogenating vegetable oil (L)

C2H4 + Br2 → C2H4Br2 - 

 This reaction can be used to test the presence of double bonds. Adding orange bromine water will decolourise the solution. Mechanism: double bond repels the electrons in Br2, polarising it (δ+ and δ-). Heterolytic fission of Br occurs, one of them (Br+) attaching itself to the C atom. Br- then attaches to the carbocation formed

 Adding hydrogen halides can cause 2 different products to be formed

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Free Radical Substituition

Halogenoalkanes from Halogens and Alkanes

CH4 + Cl2 → CH3Cl + HCl

1. INITIATION - UV light forms Cl radicals   -        Cl2 → 2Cl・

2. PROPAGATION       -             Cl・+ CH4 → CH3・ + HCl

Repeated until no Cl2/CH4 CH3・+ Cl2 → CH3Cl + Cl・


e.g. CH3・+CH3・→ C2H6

Problems: Yield of CH3Cl isn't high as a mixture of products formed.

4. Further Substituition  CH3CL → CH2Cl2 

CH2Cl2 → CHCl3

CHCl3 → CCl4

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Alkenes - Unsaturated hydrocarbons, has one or more double bonds CnH2n. Double bonds are reactive, they can open to join with other atoms. A double bond is made up of:    σ - sigma bond - 2 s-orbitals overlap in a straight line - there's high electron density between them, which attracts electrophiles             π - pi bond - 2 p-orbitals overlap. There are two parts to it - one above and one below the molecule, as the orbitals are dumb-bell shaped.Double bonds cannot rotate due to this, causing cis/trans isomerism.

Addition polymerisation: double bonds in alkenes open up and join together to form long chain polymers ethene becomes poly(ethene)      

Poly(chloroethene), also known as PVC, has a wide range of uses such as insulation on wires and water pipes   

Poly(tetrafluoroethene), also known as PTFE, is useful on frying pans as they have non-stick properties

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Hydroxyl Group -OH - Primary alcohols have 1 alkyl group attached to the OH carbon. Secondary alcohols have 2 alkyl groups, tertiary have 3. Small alcohols are miscible with water, as hydrogen bonds form between them (hydroxyl group of the alcohol is polar and so are the water molecules). Polar nature decreases as the size of molecule increases. Uses of ethanol: alcoholic drinks, methylated spirits (industrial solvent with purple dye, making it undrinkable), bioethanol

How they are made

1. Hydration of ethene (Hot Phosphoric Acid / 300℃ / 60atm

C2H4(g) + H2O(g) ⇔ C2H5OH(g)

Dehydration reverse reaction: phosphoric acid catalyst, 170℃

2. Fermentation of glucose (30-40℃ / Anaerobic Conditions / Yeist)

C6H12O6(aq) → 2C2H5OH(aq) + 2CO2(g)   -    

This is an exothermic reaction. Yiest dies when over 15% ethanol. Fractional distillation increases concentration of ethanol.

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Esterification (Conc Sulfuric Acid)

alcohol + carboxylic acid ⇔ ester + water

e.g. ethanol + ethanoic acid ⇔ ethylmethanoate + water

CFCs (chlorofluorocarbons)

Stable due to strong halogen-carbon bonds, volatile, non-flammable and non-toxic – CFCs found in aerosol cans, fridges, and air conditioning, until we found out that they were destructing the ozone layer. Alternatives: HCFCs (hydrochlorofluorocarbons), HFCs (hydrofluorocarbons) – these are temporary alternatives to CFCs. Less/no chlorine means less ozone depletion. They are eventually broken down in the atmosphere. However, these are much worse than CO2 molecules in terms of enhancing of the greenhouse effect. Nowadays aerosols have pump spray systems and ammonia is used in fridges, and CO2 is used to make foamed polymers instead of CFCs.

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Oxidation of Alcohols

Oxidation of alcohol (Acidified Potassium Dichromate)

Combustion oxidises alcohols - they can be distilled/refluxed using an oxidising agent which turns from orange to green

PRIMARY ALCOHOLS distilled with oxidising agent producing ALDEHYDEs 

ethanol + [O] → ethanal + water C2H5OH + [O] → CH3COH + H2O

To prevent further oxidation (forming carboxylic acid), removal of the aldehyde out of the oxidising solution is needed as soon as it is formed.

CARBOXYLIC ACID - REFLUX (continual heating) so that it is vigorously oxidised Vapourised compounds are condensed back into the reaction mixture with a vertical condenser.

ethanal + [O] → ethanoic acid CH3COH + [O] → CH3COOH

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Infrared Spectroscopy

SECONDARY ALCOHOLS are oxidised to KETONES when refluxed with the oxidising agent.

propan-2-ol + [O] → propanone + water

CH3CH(OH)CH3 + [O] → CH3C=OCH3 + H2O

Ketones cannot be oxidised further by refluxing. Also, TERTIARY ALCOHOLS are not easily oxidised with oxidising agents (the only way is to burn).

Infrared spectroscopy – identifying molecules - Infrared radiation is passed through chemical sample. Different covalent bonds absorb different frequencies of this radiation. The graph shows ‘peaks’ at specific frequencies to show which bond is present.

Uses: breathalysing a driver will show the amount of ethanol vapour in their breath. CO absorbs a certain frequency of infrared radiation so it can be passed through sample air to identify CO gas.

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Hydrolysis of Halogenoalkanes

Hydrolysis of halogenoalkanes - Nucleophilic Substitution

Halogens are more electronegative than carbon, thus carbon-halogen is polar. This means that C (δ+) easily attracts the nucleophiles (electron pair donator) e.g. OH- Bromomethane can be hydrolysed to ethanol:

C2H5Br + OH- → C2H5OH + Br-

Bond enthalpy decreases down the halogen group so iodoalkanes are hydrolysed the fastest (weaker bonds can be broken more easily).

OH- comes from warm aqueous potassium hydroxide (KOH) or sodium hydroxide (NaOH) and this is done under reflux.

Mechanism: OH- is attracted to the δ+ in C of bromomethane. Heterolytic fission of C-Br – electron pair is taken by Br. OH- attaches to the carbocation as Br- falls off.

C2H5Br + H2O → C2H5OH + H3O+ + Br-

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Mass Spectrometry

Mixing halogenoalkanes with water forms alcohol and aqueous halide (here, H2O is the nucleophile). You can compare the reaction rates of different halogenoalkanes by adding silver nitrate (AgNO3) solution:                              Ag+ + Br- → AgBr (silver halide)                Iodoalkane - White precipitate    Bromoalkane - Cream precipitate      Chloroalkane - Yellow precipitate

  Mass spectrometry - Uses: Probes to Mars have carried mass spectrometers to identify molecules on the planet. Level of pollutants in the air can be studied.

 Mass spectrum gives mass/charge on the x-axis and the abundance on the y-axis. Molecules are bombarded with electrons to produce + ions of different fragments, and the bar represents molecular mass of the fragment.

Useful in differentiating between molecules that have the same molecular formula such as propanone and propanal, however propanal will have a C2H5+ fragment.

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Electrophilic Addition - Alkene + HBr ----------------> Halogenoalkane
Nucleophilic Substitution - Halogenoalkane -------> Alcohol
Free Radical Substitution - Alkane + Chlorine -----> Chloroalkane
Elimination - Alcohol + H2SO4 -------------------------> Alkene
Oxidation- Primary Alcohol + K2Cr2O7 + H2SO4 --->Aldehyde or Carboxylic Acid

Hydration(300'C / 60 atm / Hot Phosphoric Acid): Ethene + Steam --> Ethanol

Halogenation OR Electrophilic Addition: Ethene + Bromine -->1,2-dibromoethane

Addition of a hydrogen Halide: Ethene + Hydrogen Bromide --> 1-bromoethane

Hydrogenation(150*C / Nickel Catalyst): Ethene + Hydrogen --> Ethane

Formation of an alcohol by hydrolysis of a halogenoalkane:                Nucleophilic substitution  / Reflux 
1-chloropropane --> propan-1-ol

(need to know mechanism ^)

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Combustion of an alcohol: CnH2n+1+(1.5n)O2 --> nCO2 + (n+1)H2O

Hydration of ethene(300*C / 60atm / Phosphoric Acid): 

Ethene + Steam --> Ethanol

Fermentation(yeast / 37*C)Glucose --> Ethanol + Carbon dioxide

Oxidation of alcohols(H2SO4 / K2CR2O7) :          Primary alcohol: propan-1-ol

Distillation: Propan-1-ol + [O] --> Propanal (aldehyde)

Reflux: Propan-1-ol + 2[O] --> Propanoic acid (carboxylic acid)

Secondary alcohol: butan-2-ol

Butan-2-ol + [O] --> Butanone (ketone)

Tertiary alcohols do not oxidise 

Dehydration of an alcohol(Reflux / H2SO4): Ethanol --> Ethene + water

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