Organic Chemistry

• Hydrocarbon - compound of carbon and hydrogen only.
• Crude oil = source of hydrocarbons.
• Complex mixture of hydrocarbons - is seperated into fractions.
• Each fraction contains a mixture of hydrocarbons with the similar boiling points..
• Tre fractions are obtained by fractional distillations.
• Short chains - low Boiling point ... condense near the top.
• long chains - high Bp ... condense near the bottom.
• Gases do not condense and pass through an outlet at the top as petroleum jelly.

• Saturated molecules.
• will not decolourise bromine water.
• Alkanes - single chained hydrocarbons.
• single C-C bond.
• Alkanes - each carbon is bonded to 4 other atoms.
• Each carbon has a tetrahedral shape.
• Each bond angle = 109.5.

• Crude oil has many fractions.
• There are weak intermolecular forces (Wan der waals forces) in order to boil these forces have to be broken.
• As the chains length increases the bp increases...more points of contact.
• therefore, more points of contact and so more wan der waals forces of attraction.
• It takes more energy and therefore a higher temperature to seperate the bonds.
• This is why alkanes in crude oil can be seperated into fractions.
• Effects of Branching
• Isomers of alkanes have the same Mr value.
• A branched isomer has a lower bp than a unbranched isomer.
• Because in a branched isomer there are fewer points of contact between molecules and therefore fewer wan der waals forces of attraction.
• Branched molecules can not get as close to each other unbranched molecules ... and therefore fewer WDW's...
• So less heat is required to seperate the molecules.

• Short chain alkanes = valuable ... as they = clean fuel.
• They burn in plentiful supply of oxygen and they for CO2 and H2O.
• Methane - main constituent for natural gas.
• CH4 + 2 O2 -----> CO2 + 2 H2O.
• This shows that methan burns cleanly with oxygen.
• Propane and butane are easily liquified and are used as liquified petroluem gas or LPG.
• IMCOMPLETE COMBUSTION
• Insuffiecient supply of oxygen.
• E.e internal combustion engine in most cars - limited supply of O2.
• Octane (fuel) undergo's incomplete combustion  ... to for CO.
• CO= colourless, poisonous gas.
• Produced when a fossil fuel is combusted in insufficient oxygen.
• CO = poisonous.
• prevent RBC's carrying O2 and so the body is starved of oxygen.

• After fraction distillation there is a surpluss of long chained hydrocarbons.
• BUT... short chained hydrocarbons are in demand.
• short chained alkanes = great fuels.
• short chained alkenes = for polymer production.
• Cracking - breakdown of long chained hydrocarbons to form a mixture of short chain alkanes and alkenes.
• Catalytic cracking ... first used mid 1930's.
• Initially Al2O3 and Silicondioxide were used as the catalysts.
• But now there are more effiecient catalytic systems.
• NOW THEY USE ZEOLITS CATALYST @ 450 degress .
• IN CRACKING - long chained alkanes are broken down randomly!!!

• Aliphatic hydrocarbons = carbon atoms attached in straight unbranched chains.
• Can be converted to cyclic and aromatic hydrocarbons.
• BY REFORMING
• H2 gas is always produced as a result of reforming.

Improving Fuels

• Research octon number rates how well fuels burn.
• Fuels with high octane rating burn close to 100% (efficiently).
• Straight chain - heptane = poor fuel and it has an actane rating of 0.
• Branched and cyclic alkanes = important petrol additives.
• They promote more efficient combustion.
• consequently branched chain alkanes = used in fuel.
• H2 gas which is produced in reforming is then recycled in the production of ammonia and margarine.
  

• Crude oil --- and the material produced from it play a big part in our life.
• sf impact on standard of living.
• We rely on crude oil for power for electrical generations.
• Use of crude oil = apparent ... produce alkanes.
• Branched and cyclic alkanes = best of fuel ...
• GOOD FUEL = readily available, inexpensive, and easily transportable.
• Oil price -- increasing.
• Now need an alternative!
• Burning hydrocarbons - increase atmospheric pollution.
• CO - incomplete combustion in the internal of a combustion engine.
• CO2 - contributes to global warming and the greenhouse effect...
• Nitrogen oxides - contribute to aciod rain and the destruction of rain forests
• Hence, increase temp on earth.

• Biofuel - derived from recently living materials - like plants and animal waste.
• Rapeseed - Agricultural crops... specially grown for energy use ... another eg... sugar cane (biodiesel).
• Ethanol - fermenting sugar and other carbs.
• burns efficiently in plentiful supply of oxygen.
• Ehtanol and petroleum can be blended together to make the fuel burn more efficiently.
• Ethanol can be used (when blended with petroluem ) in engines without any need for majour modifications ...
• sf reduced harmful gases that are produced.
• Bioethanol - getting a big boost.
• First plant located in somerset.
• Capable of producing 105000 tonnes of bioethanol.

• Fuel oil.
• Derived from rapeseeds.
• Compatible with engines - can be used 100 % pure.
• However, usually plended with normal diesel.
• Motor fuel being produced from sugar can = long term interest ...
• Because crude oil = finite.
• crude oil - millions of year to produce.
• Ethanol - alternative source for fuel (produced from sugar cane).
• sugar cane - annual crop.
• BRAZIL - produces ethanol from sugar cane... climate favour this means of production.
• And it has few oil reserves of its own.
• Fossil fuel = non renewable.
• Ethanol - produced from hydration of ethene and fermentation
• Increased CO2 lvls from combustion of fossil fuels - leads to global warming and climate change.

• Using alkanes and UV radiation.
• by Cl2 and Br2 to form halogenoalkanes.
• Halogen react with alkanes in the presence of UV radiation or at temp above 300degs .
• Methane reacts with chlore = a readical substitution.
• Radical substitution - reaction where radical replaces ... different atom.
• COVALENT BONDS = BROKEN BY HOMOLYTIC FISSION TO FORM RADICALS WITH UNPAIRED ELECTRONS.
• A hydrogen atom in the alkane is substitued with a halogen.

• The Cl-Cl bonds are broken by homolytic fission ... forming 2 free radicals Cl* and Cl*.
• UV RADIATION - provides the enrgy for the bond fission.
  
• Cl-Cl -------------> Cl* + Cl* (The * represents the free radical... normall it is a fullstop).
  

• Alkenes and cycloalkenes = unsaturated.
• They have atleast one double bond.
• THEY DECOLOURISE BROMINE WATER.
• A sigma bond is formed between the 2 carbon atoms (from the s-subshell).
• Each carbon contributes 1 electron.
• Pi - bonds form above and below the plane of the carbon atoms.
• There is an overalp of the P-orbitals.
• Each carbon atom contributes 1 electron from a p-orbital to the pi bond.

• Pi-bond fixes the carbon atoms in a fixed position - at either end of the double bond.
• This prevent rotation.

• 3 regions of electron density surround each carbon in the double bond.
• The Pair of electrons repel each other far apart to minimise repulsion.
• Gives a trigonal planar shape.
• 120 degrees..
• Ethene = flat trigonal planar.
• Cyclic Alkenes.
• Closed rings of carbon atoms - containing one or more double bonds.
• Most common cyclic alkene - cyclohexene.
• Don't follow the same formula as alphatic alkenes.

GOOD LUCK!!