Organic chemistry

• Crude oil:

  A finite resource found in rocks

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

  Is a mixture of a very large number of compounds

  It's impossible to separate substances in the mixture by physical methods

  Most of the compounds in crude oil consist of molecules made up of hydrogen and carbon only. Most of these saturated hydrocarbons are alkanes
• Hydrocarbons:

  Have the general formula: Cn H2n+2

  The first four alkanes are methane, ethane, propane, and butane

  Alkene molecules can be presented in the following forms:

  
• Fractional distillation

  1. Oil is heated in the fractionating column

  2. Oil evaporates and condenses at several different temperatures

  3. The many hydrocarbons in crude oil can be separated into fractions each of which contains molecules with a similar number of carbon atoms

  4. The fractionating column works continuously, heated crude oil is piped in at the bottom

  5. The vapourised oil evaporates and rises the column and the various fractions are constantly tapped off at the different levels where they condense
• Fractions

  Contain molecules with a similar number of carbon atoms
• The fractions can be processed to produce fuels and feedstock for the petrochemical industry
• Many of the fuels we depend on for our modern lifestyle are made from crude oil
• The petrochemical industry produces many useful materials on which modern life depends, e.g., solvents, lubricants, polymers, and detergents
• The vast array of natural and synthetic carbon compounds occurs due to the ability of carbon atoms to form families of similar compounds
• Properties of hydrocarbons:

  • Some properties of hydrocarbons depend on the size of their molecules. These properties influence their use as fuels.
  • The shorter the molecules, the less viscous it is (more runny)
  • The shorter the molecules, the lower the melting and boiling point
  • The shorter the molecules, the more flammable it is
  • Hydrocarbons are burnt so that they can be used as fuel, since the reaction produces energy: Hydrocarbon -> carbon dioxide + water
• Cracking:

  Hydrocarbons can be cracked to produce smaller, more useful molecules.

  Some products of cracking are made from cracking are useful as fuels, since they have shorter chains than the alkenes you started with, making them more flammable and so a better fuel

  This process involves heating the hydrocarbons to vapourise them. These processes are:

  • Passing them over a hot catalyst (catalytic cracking)
  • OR mixing them with steam and heated to a very high temperature so that thermal decomposition reactions can occur (steam cracking)
• Alkenes:

  alkanes have a general formula CnH2n

  They have at least one carbon-carbon double bond making them unsaturated as they contain two fewer hydrogen atoms than the alkanes with the same number of carbons

  The first four alkenes are ethene, propene, butene, and pentene

  Unsaturated carbons can be represented in the following forms:

  
• Reactions of alkenes:

  Alkenes are hydrocarbons with the functional group C=C.

  They react with oxygen in combustion reactions in the same way as other hydrocarbons, but they tend to burn with a smokey flame because of incomplete combustion.

  They also react with hydrogen, water, and the halogens, by the addition of atoms across the carbon-carbon double bond so that the double bond becomes a single carbon-carbon bond.

  In every reaction with hydrogen, water, and halogens:
• Alcohols:

  Alcohols contain the functional group -OH

  
• Reactions of alcohols:

  They burn in air which produces carbon dioxide and water.

  They dissolve in water to form a neutral solution.

  They react with sodium to produce hydrogen and a salt.

  They react with oxidising agents to form carboxylic acids.
• Uses of alcohols:

  Methanol: chemical feedstock, in anti-freeze, to make biodiesel

  Ethanol: the main alcohol used in alcoholoc drinks, used as a solvent and furl

  All four: used as fuels
• Producing ethanol:

  Ethanol can be produced by fermentation of sugar with yeast, using renewable sources.

  Conditions: about 35 degrees Celcius, anaerobic and yeast enzyme catalyst.

  Sugar -> ethanol + carbon dioxide
• Carboxylic acids:

  Ethanoic acid is a member of the carboxylic acids.

  They have the functional group -COOH.

  The first four members are methanoic acid, ethanoic acid, propanoic acid, and butanoic acid.

  
• Reactions of carboxylic acids:

  They dissolve in water to produce acidic solutions.

  They react with metal carbonates to produce carbon dioxide, a salt and water.

  React with alcohols in the presence of an acid catalyst to produce esters.

  They do not completely ionise in solutions, so they do not release many H+ ions, making carboxylic acids weak acids.

  React with alcohols to produce esters:

  
• Addition polymerisation:

  Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation. In this reaction, many small molecules (monomers) join to create very large molecules (polymers).

  The repeat unit has the same amount of atoms as the monomer because no other molecule is formed in the reaction.

  
• Condensation polymerisation:

  Involves monomers with two functional groups.

  • When they react, they join together, usually losing small molecules such as water, and so the reactions are called condensation reactions.
  • The simplest polymers are produced from two different monomers with two of the same functional groups on each monomer.

  
• Amino acids:

  They have two different functional groups in a molecule [an amine group and a carboxylic acid group].

  They react by condensation polymerization to produce polypeptides [works the same as the polyester above just has different functional groups].

  Different amino acids can be combined in the same chain to produce proteins.
• DNA [deoxyribonucleic acid]:

  [deo] = double helix, [deoxy] = deoxyribose sugar, [ribose] = ribose sugar
• DNA:

  DNA is a large molecule essential for life - it encodes genetic instructions for the development and functioning of living organisms and viruses.

  Most molecules are two polymer chains, made from four different monomers called nucleotides, in the form of a double helix.

  Other naturally occurring polymers important for life...

  • Proteins [monomer = amino acid], starch [monomer = glucose] and cellulose [monomer = glucose].