organic chemistry

• Organic


  Study of carbon compounds extracted from living organisms
• Hydrocarbon


  Class of organic compounds containing carbon & hydrogen only - covalently bonded
• Types of hydrocarbons

  • Alkanes -> saturated hydrocarbons
  • Alkenes -> unsaturated hydrocarbons
• Alkanes


  • Saturated hydrocarbons
  • Family of organic compounds in which the carbon atoms are single bonded
• Functional group of alkanes


  [C-C] single covalent bonds between carbon atoms
• Homologous series


  Family of organic compounds with same functional group = same chemical properties, same general formula, difference between 2 successive members are constant
• Chemistry of alkanes

  • Only undergo substitution reaction where Hydrogen replaced by monovalent atom in presence of light
• Organic solvents

  • CHCl3 (chloroform)
  • CCl4 (carbon tetrachloride)
  • are volatile, have low boiling point and are flammable
• Alkanes

  • Burn in excess oxygen to give CO2 & H2O
  • Used as fuels
  • main constituent of natural gas is methane
• Alkenes


  Unsaturated hydrocarbons, organic compounds with a double covalent bond between carbon atoms

  general formula -> [ Cn H2n ]

  functional group -> c double bond c
• Alkenes


  • Form homologous series
  • Undergo addition reactions
  • have same general formula
  • have same functional group so have same chemical properties
• Addition reactions of alkenes

  2 monovalent atoms (radicals) are added to 2 adjacent carbon carrying the double bond which will break down to give a single bond, forming saturated compound
• Addition reactions of alkenes

  • Hydrogenation - in presence of nickel catalyst and heat
  • alkene + hydrogen -> alkane
  • Halogenation
• Hydration of alkenes


  Alkene + Steam -> Alkanol, in presence of phosphoric or tungestic acid + heat and pressure
• Alkanes undergo substitution which give 2 products, alkenes undergo addition which gives only 1 product
• Test for unsaturation (presence of double bond)

  • Using aqueous bromine/bromine dissolved in CCl4 (orange) - alkane no change, alkene decolourisation
  • Using acidified potassium manganate VII (purple) - alkane no change, alkene decolourisation
• Alkenes burn in good supply of oxygen to give CO2 & H2O and a large amount of heat, so they can be used as fuels
• Isomers

  Organic compounds with same molecular formula & different structural formula
• Crude oil (petroleum)

  Complex mixture of saturated hydrocarbons (alkanes) of similar boiling points, can be separated by fractional distillation but each section is still a mixture of alkanes
• Products of fractional distillation of crude oil

  • Refinery gas - heating and cooking
  • Petrol - fuel for cars
  • Naphtha - chemicals
  • Kerosene - jet fuel and used in stoves
  • Diesel oil - fuel for diesel engines
  • Fuel oil - fuel for ships and home heating systems
  • Lubricating oil - lubricants, waxes and polishes
  • Bitumen - roads and roofs
• Cracking


  Breakdown of long chain alkanes to small chain alkanes to obtain more petrol
• Cracking

  • Thermal cracking (high temp and pressure)
  • Catalytic cracking (in presence of catalyst)
• Cracking of alkanes can produce alkenes & hydrogen making it an industrial process to prepare hydrogen like electrolysis
• Alcohols (alkanols)


  Homologous series of compounds of alkanes in which a hydrogen atom is replaced by an OH group
• General formula (alcohols)

  CnH2n+1OH or CnH2n+2O
• Industrial preparation of ethanol

  1. Catalytic hydration of ethene gas

  2. Fermentation of sugar in presence of yeast
• Fermentation

  • Max ethanol concentration 15%, if exceeded yeast will die
  • If 100% ethanol needed, fractional distillation is used
  • Optimum temp 35-40°C
  • Ethanol can oxidise to ethanoic acid if air enters apparatus
  • what is seen during fermentation? - bubbles of CO2
  • - froth is obtained
• Fermentation is a process of biotechnology, using micro-organisms in production of compounds
• Alcohols

  • undergo oxidation to give corresponding acid. slow when done in air and can be sped up by oxidising agents such as potassium manganate VII and potassium dichromate VI
  • alkanols are reducing agents
  • Alkanol + 2 oxygen -> Alkanoic acid (oxygen given by oxidising agent)
  • Burn to give clean flame in exothermic reaction
• Uses of ethanol

  • Alcoholic drinks
  • Solvent
  • Fuel
• Carboxylic acids (alkanoic acids)


  Compounds with a carboxyl functional group [-C(=O)OH]
• General formula (carboxylic acids)

  CnH2nO2 or CnH2n+1COOH
• Preparation of ethanoic acid

  Oxidation of ethanol by oxidising agent or bacterial oxidation
• Carboxylic acids

  • Weak acids, partially ionise in water
  • Can react with bases & carbonates
• Esterification reaction


  Organic acid + Alcohol -> Ester + Water, using sulfuric acid as catalyst
• Esters


  Have a fruity smell, used for flavouring food & perfumes
• Dehydration of ethanol


  Ethanol -> Ethene, using concentrated H2SO4 (sulfuric acid) or Al2O3 & high temp or pumice stone & high temp
• Formation of alkyl


  Alkane - hydrogen -> alkyl
• for alkanes to react with bromine it should be used as liquid Br2 without dissolving in solvent and reaction must be in presence of light
• ethene is not used as fuel because it is used for manufacturing some industrial products like polyethene (plastic) and ethanol