Chemistry - topic 7 - Organic Chemistry

A hydrocarbon is any molecule that is formed from carbon and hydrogen atoms only.

• The simplest type of hydrocarbons called alkanes.
• Alkanes are made up of chains of carbon atoms surrounded by hydrogen atoms.
• Carbon atoms form four bonds and hydrogen atoms only form one bond.
• In alkanes, there are no carbon-carbon double bonds so all the atoms formed bonds with as many other atoms as they can- this means they're saturated.
• Different alkanes have chains of different lengths.
• The first four alkanes are methane, ethane, propane, and butane.
• Methane has just one carbon atom and four hydrogen atoms, so its chemical formula is CH_4.
• Ethane has a chain of two carbon atoms and the chemical formula of C₂H_6.
• Propane has a chain of three carbon atoms and the chemical formula C₃H_8.
• Butane has a chain of four carbon atoms and the chemical formula C₄H_10.
• The general formula for alkanes is C_nH_2n+2.

• The properties of hydrocarbons change depending on the length of the carbon chain.
• There are three trends in the properties of hydrocarbons:
  • The shorter the molecules, the more runny the hydrocarbon is - the less viscous it is.
  • The shorter the molecules, the lower their boiling point is.
  • The shorter the molecules, the more flammable the hydrocarbon is.
• Hydrocarbons with very long carbon chains are viscous, have very high boiling points and are not very flammable.

• If you burn hydrocarbons, the carbon and hydrogen react with oxygen from the air to form carbon dioxide and water vapour.
• The carbon and hydrogen are oxidised and energy released.
• When there's plenty of oxygen, all the carbon atoms are completely oxidised and this is called complete combustion.
• The equation for the complete combustion of a hydrocarbon is:
• Hydrocarbon + oxygen ----> carbon dioxide + water vapour

• Crude oil is a mixture of many different compounds.
• It's formed from the remains of plants and animals, mainly plankton, that died millions of years ago and were buried in mud. Over millions of years, with high temperature and pressure, the remains turn to crude oil,  which can be drilled up from rocks where it's found.
• Because it takes so log to form crude oil is said to be a finite resource.
• Most of the compounds in crude oil are hydrocarbon molecules, and the majority of them are alkanes.

• Fractional distillation can be used to split crude oil into seperate groups of hydrocarbons.
• The crude oil is pumped into a piece of equipment known as a fractionating column, which works continuously and has a temperature gradient running through it where the bottom is the hottest point and the top the coldest point.
• The crude oil is first heated so that it evaporates and is then piped in at the bottm of the column. The gas rises up the column and gradually cools.
• Different compounds in the mixture have different boiling points, so they condense at different temperatures meaning they condense at different levels in the fractionating column.
• Hydrocarbons that have similar numbers of carbon atoms ave similar boiling points and so condense at similar levels in the column.
• The groups of hydrocarbons that condense together are called fractions.
• The various fractions are constantly tapped off from the column at the different levels where they condense.

• Fractions from crude oil can be processed to provide the fuel for most modern transport. Diesel oil, petrol, kerosene, heavy fuel oil and LPG (liquefied petroleum gases) are used to fuel cars, trains, planes and other forms of transport.
• The uses of hydrocarbons depend on their properties.
• Examples:
  • The LGP fraction has the lowest boiling point and is a gas at room temperature making it ideal for using as bottled gas. It's stored under pressure as liquid in bottles. When the tap on the bottle is opened, the fuel vaporises and flows to the burner where it's ignited.
  • The petrol fraction has a higher boiling point. Petrol is liquid at room temperature. It can flow to the engine where it's easily vaporised to mix with the air before it is ignited.
  • The really gloopy, viscous hydrocarbons are used for lubricating engine parts or covering roads

• The petrochemical industry uses some of the hydrocarbons from crude oil as a feedstock to make new compounds for use in things like polymers, solvents, lubricants and detergents.
• All products from crude oil are examples of organic compounds. A large variety of products from crude oil is because carbon atoms can bond together to form different groups called homologous series.
• Alkanes, alkenes, as well as other families such as alcohols and carboxylic acids, are all examples of different homologous series.

• Short-chain hydrocarbons are flammable so make good fuels and are in high demand however, long-chain hydrocarbons form thick gloopy liquids like tar which aren't useful. This is why a lot of the longer molecules produced from fractional distillation are turned into smaller, more useful ones by cracking.
• Some products of cracking are:
  • petrol for cars
  • paraffin for jet fuel
  • Ethene, used for making plastics
  • 

• Cracking is a thermal decomposition reaction- breaking molecules down by heating them.
• There are two methods used to crack alkanes:
  • Catalytic cracking
  • Steam cracking
• In both, the first step is to vaporise the long-chain hydrocarbon by heating.
• In Catalytic cracking:
  • the vapour is then passed over a hot, powdered catalyst (e.g. aluminium oxide). The long-chain molecules split apart or 'crack' on the surface of the specks of catalyst
• In steam cracking:
  • the vapour can is mixed with steam and heated to a high temperature, also leading to thermal decomposition of long-chain hydrocarbon molecules to form smaller ones

• Most products of cracking are alkanes and alkenes (unsaturated hydrocarbons)
• Example:
  • Decane is a long-chain hydrocarbon molecule and there is large amounts in crude oil.
  • Cracking is used to break decane down into octane and ethene, as it's not useful on its own.
  • Octane is a shorter-chain alkane which is useful for making petrol.
  • Ethene is an alkene which is useful for making plastics. 

• Alkenes are a homologous series of hydrocarbons.
• They're more reactive than alkanes.
• They have a double covalent bond between two of the carbon atoms in their chain.
• They are known as unsaturated because they contain two fewer hydrogen atoms than alkanes with the same number of carbon atoms.
• 
• The C=C double bond can open up to become a single bond, allowing the two carbon atoms to bond with other atoms.
• The first four alkenes are ---> ethene, propene, butene and pentene.
• The general formula for alkenes is C_nH_2n

• In large amounts of oxygen, alkenes ombust completely to produce water and carbon dioxide.
• But, there isn't enough oxygen in the air for this, so when burned they tend to undergo incomplete combustion. Carbon dioxide and water are still produced but cabron and coarbon monoxide can aslo be emitted.
• Alkene+Oxygen --> Carbon+Cabron Monoxide+Carbon Dioxide+Water (+ Energy)
• Incomplete combustion results in a smoky yellow flame and the release of less energy compared to the complete combustion of the same compound.
• An example incomplete combustion of an alkene is:
• C₄H₈ + 5O₂ --> 2CO + 2CO₂ + 4H₂O

• A functional group is a group of atoms in a molecule that determine how the molecule typically reacts. All alkenes have the functional group 'C=C', so they all react in similar ways.
• Most of the time alkenes react via addition reactions. The carbon double bond will open up to leave a single carbon bond and a new atom is added to each carbon atom.
• In hydrogenation, hydrogen is added to the alkene. Hydrogen reacts with the double bonded carbon to open up the bond and form the equivalent, saturated alkane.
• Steam can react to form alcohols. When alkenes react with steam, water is added across the double bond and alcohol is formed. For example, ethonal can be made by mixing ethen with steam and passing it over a catalyst. The coversion of ethene to ethanol is one way of making ethonl industrially. After the reaction takes place, the reaction mixture is passed into a condenser. Ethanol and water have higher bioling points than ethene, so both condense wi=hile any unreacted ethene is recycled back into the reactor. The alcohol can then be purified by fractional distillation.
• Alkenes will also react in addition reactions with halogens such as bromine, chlorine and iodine. The molecule formed is saturated with the c=c bond opening up and each carbon atom bonding to a halogen atom. For example, bromine and ethene react to form dibromoethane.
• The addition of Bromine to a double can be used to test for alkenes. If bromine water is added to asaturated compound like an alkane, no reaction will happen and it'll stay bright orange. If it's added to an alkene it will make a dibromo-compound that is colourless.

• Polymers are long molecules formed of lots of small molecules called monomers joined together. This reaction is called polymerisation and usually needs hig pressure and a catalyst.
• Plastics are made of polymers. They're usually carbon based and their monomers are often alkenes.

• The monomers that make up addition polymers have a double covalent bond.
• Lots of unsaturated monomer molecules (alkenes) can open up their double bonds and join togeher to form polymer chains. This is called addition polymerisation.
• When monomers react in addition polymerisation, the only product is the polymer, so an addition polymer contains exactly the same type and number of atoms as the monomer that formed it.

• The general formula for an alcohol is C_nH_2n+1OH. 
• All alcohols contain an -OH group. The first four in the homologous series are: methanol, ethanol, propanol and butanol. 
• The basic naming system is the same for alkanes but replacing the 'e' with '-ol'
• The first four alcohols have similar properties.
• Alcohol are flammable and they undergo complete combustion in air to produce carbon dioxide and water.
• Methanol, ethanol, propanol and butanol are all soluble in water. Their solutions have a neutral pH. They also react with sodium, one of the products of this reaction is hydrogen.
• Alcohols can be oxidised by reacting with oxygen to produce a carboxylic acid.
• Different acids form different carboxylic acids. For example, methanol forms methanoic aicd and ethanol form ethanoic acid.
• Alcohols such as ethanol and methaol are used as solvets in industry because they can dissolve most things water can dissolve, but can also dissolve substances that water cannot dissolve.
• The first four alcohols are also used as fuel. e.g. ethanol is used as fuel in spirit burners as it burns fairly cleanly and does not smell.

• Ethanol is the alcohol found in most alcoholic drinks and is made using fermentation.
• Fermentation uses a catalyst found in yeast to convert sugars into ethanol. The reaction occurs in solution so the ethanol produced is aqueous and carbon dioxide is also produced.
• Fermentation happens fastest at room temperature, 37°c, in a slightly acidic solution and under anaerobic conditions.
• Under these conditions the ezyme in yeast works best to convert sugar to ethanol. If these conditions changed, the enzyme could become denatured or work at a slower rate.

• Carboxylic acids are a homologous series of compounds that all have '-COOH' as a fucntional group. Their names end in '-anoic acid' and begin with the alkane name with the '-ane' removed
• They react with carbonattes to produce a salt, water and carbon dioxide.
• The salts formed in these reactions end in '-anoate'. e.g. methanoic acid will form methanoate.
• Carboxylic acids can dissolve in water, when they dissolve they ionise and release H⁺ resulting in an acidic solution. But they don't completely ionise so form weak acidic solutions.
  

• Esters have the functional group '-COO-'
• Esters are formed from an alcohol and a carboxylic acid.
• An acid catalyst is also usually used to speed up the reaction. e.g. concentrated sulfuric acid.
• Alcohol + Carboxylic Acid --> Ester + Water

• Condensation polymerisation involves reacting together monomers containing different functional groups so that bonds form between them and they form a polymer chain.
• For each new bond that forms, a small molecule is lost.
• The simplest type of condensation polymers have contain two different types of monomer, each with two of the same functional groups.
• E.g. Polyester=
  • n(HO-CH₂-CH₂-CH₂-OH) + n(HOOC-CH₂-CH₂-CH₂-CH₂-COOH)
  • --> n(CH₂-CH₂-O-CO-CH₂-CH₂-CH₂-CH₂-CO-O) + 2nH₂O

• Number Of Types Of Monomers:
  • Addition polymerisation- only one monomer type containing a c=c bond
  • Condensation polymerisation- two monomer types each containing two of the same functional groups. OR one monomer type with two different functional groups.
• Number Of Products-
  • Addition polymerisation- only one product formed
  • Condensation polymerisation- two types of product, one polymer one small molecule.
• Functional Groups Involved In Polymerisation-
  • Addition polymerisation-carbon-carbon double bond in monomer.
  • Condensation polymerisation- two reactive groups on each monomer.

• Amino Acids:
  • An amino acid contains two different functional groups- a basic amino acid (NH₂) and an acidic carboxyl group (COOH)
• Proteins:
  • Amino acids can form polymers known as polypeptides via condensation polymerisation.
  • The amino group of one can react with the acid group of another to form a polymer chain. For every new bond formed a water molecule is lost.
  • One or more long chains of polypeptides are known as proteins.
  • Polypeptides and proteins can contain different amino acids in their polymer chains, and the order of these amino acids is what gives proteins their different properties and shape.
• DNA:
  • It's a large molecule that takes a double helix structure.
  • DNA is made of two monomers called 'nucleotides'. The nucleotides each contain small molecules known as bases.
  • The bases on the polymer chains pair up with each other and form cross links keeping the two strands of teh nucleotides together and giving the double helix structure.

• Simple Sugars:
  • Sugars are small molecules that contain carbon, oxygen and hydrogen.
  • Sugars can react together in polymerisation reactions to form larger carbohydrate polymers, e.g. starch.