Organic Chemistry

• Homologous series: group of organic compounds that react in a similar way as they have the same functional group

  Functional group: group of atoms that determine the main chemical properties of an organic compound
• • Crude oil is...

  o a finite resource found in rocks

  o the remains of an ancient biomass consisting mainly of plankton that was buried in mud

  o a mixture of a very large number of compounds – these compounds are mainly hydrocarbons

  • Hydrocarbons are molecules made up of hydrogen & carbon atoms only
• • Most of the hydrocarbons in crude oil are alkanes

  o The general formula for the homologous series of alkanes is CnH2n+2

  o Alkanes are saturated compounds – each carbon atom forms 4 single covalent bonds
• Methane - CH4

  Ethane - C2H6

  Propane - C3H8

  Butane - C4H10

  
• • The hydrocarbons in crude oil can be separated into fractions by fractional distillation (physical separation)

  1. The crude oil is heated until most of it has turned into a gas

  2. The gas enters a fractionating column – there is a temperature gradient (hot at bottom, cold at top)

  3. The longer hydrocarbons have higher boiling points, they condense back into liquids & drain out of the

  column early on (near the bottom)

  4. The shorter hydrocarbons have lower boiling points, they condense & drain out much later on (near top)
• • Uses of hydrocarbons from crude oil

  o Fuels for modern transport: petrol, diesel oil, kerosene, heavy fuel oil & liquefied petroleum gases

  o Feedstock to make new materials: solvents, lubricants, polymers & detergents (in the petrochemical industry)
• • As the length of the hydrocarbon increases...

  o Boiling point increases (less volatile)

  o Viscosity increases (the liquid becomes thicker/less runny)

  o Flammability decreases (harder to ignite)

  • These properties influence how the hydrocarbon is used as fuel

  o E.g. short chain hydrocarbons with lower boiling points can be stored as liquid in bottles
• • The combustion of hydrocarbon fuels release energy (the reaction is exothermic)

  o The carbon & hydrogen in the fuels are oxidised (in terms of gaining oxygen)

  • The complete combustion of hydrocarbons produces carbon dioxide & water e.g. methane

  o Methane + oxygen → carbon dioxide + water (+energy)

  o CH4 (g)+ 2O2 (g) → CO2 (g) + 2H2O (l)
• o Catalytic cracking

  ▪ Heat long-chain hydrocarbons to vaporise them (change to a gas)

  ▪ Pass the vapour over a hot catalyst (aluminium oxide)

  ▪ The molecules split apart onto the surface of the catalyst
• o Steam cracking

  ▪ Vaporise the hydrocarbons & mix them with steam

  ▪ Heat the mixture to a very high temperature which causes thermal decomposition
• • The products of cracking include alkanes & alkenes
• • There is a high demand for fuels with small molecules & so some of the products of cracking are useful as fuels

  o Long-chained hydrocarbons are thick liquids so are less useful

  o Alkanes are often used for fuels e.g. petrol for cars or paraffin for jet fuel

  o Alkenes are often used to create polymers e.g. plastic
• • Alkenes are hydrocarbons with a double carbon-carbon bond

  o The general formula for the homologous series of alkenes is CnH2n

  • Alkene molecules are unsaturated because they contain 2 fewer hydrogen atoms than the alkane with the same number of carbon atoms

  • The double bond can open up to make a single bond allowing the 2 carbon atoms to bond with other atoms

  o This makes alkenes far more reactive than alkanes
• • Alkenes react with bromine water & the water changes colour from orange to colourless
• • alkenes are hydrocarbons with the functional group C=C

  • alkenes react with oxygen in combustion reactions in the same way as other hydrocarbons, but they tend to burn in air with smoky yellow flames because of incomplete combustion (produces less energy than complete)

  o alkene + oxygen → carbon + carbon monoxide + carbon dioxide + water
• o hydrogen (hydrogenation)

  ▪ hydrogen reacts with alkenes and opens up the carbon double bond to form the equivalent saturated alkane e.g. ethene + hydrogen → ethane

  ▪ a catalyst must be present
• o halogens

  ▪ alkenes react in addition reactions with halogens to form a saturated molecule with the C=C bond carbons each bonding to a halogen atom

  ▪ e.g. ethene + bromine → dibromoethane

  • this is because the atoms are added across the C=C bond so it becomes a single C-C bond

  
• o water

  ▪ when alkenes react with steam, water is added across the carbon double bond to form an alcohol (the alkene is mixed with steam and passed over a catalyst)

  ▪ e.g. ethene + water → ethanol

  
• Reactions

  • alcohols are flammable (undergo complete combustion in air)

  o e.g. ethanol + oxygen → carbon dioxide + water

  • alcohols react with sodium to produce a salt and hydrogen

  o e.g. ethanol + sodium → sodium ethoxide + hydrogen

  • alcohols react with an oxidising agent to form carboxylic acids (next section)

  • alcohols dissolve in water (are soluble in water) forming a neutral solution (pH 7)
• Uses of alcohols

  • methanol, ethanol, propanol and butanol are all used as fuels e.g. ethanol is used in spirit burners as it burns fairly cleanly and is non-smelly

  • methanol and ethanol are used as solvents in industry (they dissolve most things water can dissolve and more) e.g. oils and fats

  • ethanol is the main alcohol in alcoholic drinks
• • aqueous solutions of ethanol are produced using fermentation of sugar solutions with yeast

  • optimum conditions: about 35°C, slightly acidic

  and anaerobic (no oxygen)

  
• general formula:CnH2n+1 OH

  • alcohols contain the functional group -OH, the first 4 in the homologous series are

  Methanol - CH3OH

  Ethanol - C2H5OH

  Propanol - C3H7OH

  Butanol - C4H9OH

  
• Carboxylic acids have the functional group -COOH, the first 4 in the homologous series are

  Methanoic Acid - HCOOH

  Ethanoic Acid - CH3COOH

  Propanoic Acid - C2H5COOH

  Butanoic Acid - C3H7COOH

  
• carboxylic acids are weak acids because when they dissolve in water they only partially ionise (not all the acid molecules release their H+ ions)

  o so they have a higher pH (less acidic) than solutions of strong acids at the same concentration
• Reactions

  • carboxylic acids react like any other acids (the salts formed end in -anoate) e.g.

  o ethanoic acid + sodium → sodium ethanoate + hydrogen

  o ethanoic acid + sodium hydroxide → sodium ethanoate + water (neutralisation reaction)

  o ethanoic acid + sodium carbonate → sodium ethanoate + carbon dioxide + water
• Esters

  • esters have the functional group -COO-, the only one you need to know is ethyl ethanoate

  • esters are formed from the reaction of an alcohol and a carboxylic acid in the presence of an acid catalyst e.g. concentrated sulphuric acid

  Esters

  • esters have the functional group -COO-, the only one you need to know is ethyl ethanoate

  • esters are formed from the reaction of an alcohol and a carboxylic acid in the presence of an acid catalyst e.g.

  concentrated sulphuric acid

  
• • alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation

  o many small molecules (monomers) join together forming very large molecules (polymers)

  o in addition polymerisation, the repeating unit has the same atoms as the monomer because no other molecule is formed in the reaction

  
• Condensation polymerisation

  • condensation polymerisation involves 2 monomers with 2 different functional groups

  o when these monomers react they join together, losing small molecules e.g. water
• • amino acids have 2 different functional groups in 1 molecule

  o they react by condensation polymerisation to produce polypeptides

  • the 2 functional groups are a basic amino group (NH2) and an acidic carboxyl group (COOH) e.g. glycine (shown to the right)

  • the amino group of an amino acid can react with the acid group of another to form a polymer chain
• • one or more long-chains of polypeptides are known as proteins which have many uses in the human body e.g.

  o enzymes work as catalysts, haemoglobin transports oxygen, antibodies are part of the immune system

  • polypeptides and proteins can contain different amino acids in their polymer chains

  o the order of amino acids is what gives the protein its distinct properties and shape
• • 2 of the same amino acids form polypeptides via. condensation polymerisation

  • 2 or more polypeptide chains join to form proteins
• Addition Polymerisation:

  • Only 1 type of monomer
  • Only 1 product formed (the polymer)
• Condensation Polymerisation:

  • 2 monomers with the same functionally groups OR 1 monomer with 2 different functionally groups
  • 2 products formed (the polymer and a small molecule e.g. water)
• • Deoxyribonucleic acid is a naturally occurring polymer of 4 different monomers called nucleotides

  o nucleotides contain a phosphate group, a deoxyribose sugar and a base (guanine, cytosine, adenine, thymine)
• • DNA is made up of 2 polymer chains of nucleotides, the bases of the 2 polymer chains pair up forming cross links keeping the 2 strands of nucleotides attached forming a double helix structure

  • DNA is found in all living organisms and some viruses, the contain genetic instructions
• • sugars are small molecules containing carbon, oxygen and hydrogen

  • simple sugars can react via. polymerisation to form large carbohydrate polymers e.g.

  o starch – used for energy storage

  o cellulose – used to strengthened cell wall in plants

  • both are polymers of glucose (C6H12O6)

  • proteins and polypeptides are also naturally occurring proteins (polymers of amino acids)