Organic

• E/Z isomer criteria


  • C=C cannot rotate
  • 2 different groups attached to each C of the C=C
• Cis-Trans Isomerism criteria


  • C=C cannot rotate
  • 2 different groups attached to each C of the C=C
  • 2 of the groups on either side of the C=C are the same
• As chain length of alkanes increases


  • More points of contact between molecules
  • More intermolecular induced dipole-dipole interactions between molecules
  • More energy is needed to break the stronger temporary dipole-dipole forces between the molecules
  • Boiling point increases
• As alkanes become more branched


  • Branched molecules cannot pack as closely together
  • There are less intermolecular temporary dipole-dipole interactions between the molecules
  • Less energy is needed to break the weaker dipole-dipole interactions between molecules
  • Boiling point decreases
• Why shorter alkanes make more useful fuels


  • Highly exothermic reactions
  • Low b.p.s to easy to ignite
• Catalytic Cracking


  Breaking down of long chain alkane into shorter, more useful hydrocarbons. Alkane -> shorter alkane + alkene
• Isomerism


  Involves heatimng unbranched molecules to form branched chain isomers which have lower b.p.s so more efficient fuel and easier to burn
• Reforming


  Conversion of cycloalkanes into aromantic hydrocarbons using a suitable catalyst to form cycloalkanes which have fewer points of contact, more efficient fuel & easier to burn.

  Hydrogen by-product is used to make fertilisers, vegetable oils
• Why is combustion of fuels an effective energy source?

  Highly exothermic reaction -> produces a lot of heat energy
• Why is incomplete combustion dangerous?

  • Toxic in a confined environment
  • Can exacerbate breathing difficulties
• Fossil Fuel Advantages & Disadvantages


  ✓ Highly exothermic

  ✗ Finite (non-renewable)

  ✗Contribute to global warming (greenhouse gas)
• Carbon Monoxide Formation & Problems


  Formed: Incomplete combustion of hydrocarbons and O₂

  Problem: Toxic
• Nitrogen Oxides Formation & Problems


  Formation: Nitrogen and Oxygen from air react at high temperatures in combustion chamber

  N₂ + O₂ -> 2NO

  Problem:

  • Converted to nitric acid, a contributor to acid rain
  • Nitrogen dioxide reacts with unburnt hydrocarbons to form 'Low-Level Ozone' (smog) which causes breathing difficulties
• Unburnt Hydrocarbons Formation & Problems


  Formation: Released in vehicle exhaust

  Problem:

  • Some are carcinogenic
  • React with Nitrogen dioxide to form 'Low-Level Ozone' (smog) which causes breathing difficulties
• Catalytic Converter


  Honeycomb structure (large SA) coated in rhodium/palladium/platinum alloy. Hot exhaust gases pass over catalytic surface & are converted into less harmful products

  1. Harmful CO and NO ADSORB (stick to surface. weak temporary bond formed) of catalytic surface
  2. CO and NO bonds weakened
  3. Chemical reaction takes place: 2NO(g) + 2CO(g) -> N₂(g) + 2CO₂(g)
  4. Less harmful products DESORB from surface of catalyst
• Alternatives to fossil fuels: Biofuels


  Biofuel: Alcohols (e.g. ethanol)

  Source:

  • Fermentation of sugars, sugar cane
  • C₆H₁₂O₆ -> 2C₂H₅OH + 2CO₂ yeast, 36°, anaerobic

  Biofuel: Biodiesel

  Source: Oils (rapeseed or cooking)
• Why are alkanes unreactive


  • carbon-hydrogen bond is non-polar
  • No multiple bonds
• Is Radical Substitution a good method for the production of a single Halogenalkane?

  No, lots of waste
• Sigma σ bond


  Single bond, formed by the 'overlap of orbitals', where each carbon atom contributes an electron to the bonding pair
• Pi π bond


  Formed above and below the plane of a molecule by 'sideways double overlap of p-orbitals'

  
• Why is C=C bond reactive

  The high electron density causes positively charged substances to be attracted towards it
• Why can HBr act as an electrophile?

  Polar molecule
• Why can Br₂ act as an electrophile?

  C=C repels e- and induces a dipole in Br₂
• When alkenes react the π bond of the C=C breaks and the σ does not


  π bond is weaker than the σ bond
• Electrophilic Addition mechanism

  
• Alkenes and Hydrogen (Hydrogenation)

  Reagents: Alkenes, Hydrogen

  Conditions: Nickel Catalyst, ~150° temp

  
• Alkenes and Halogens


  Reagents: Alkene, Halogen

  Condtions: RTP

  
• Alkene and Hydrogen Halides

  
• Alkene and Steam (Hydration)


  Reagents: Alkene, Steam

  Conditons: High temp, High pressure, concentrated phosphoric acid catalyst

  
• Markowinkoff's Rule

  
• Alkene reactions

  
• Addition polymerisation

  
• Use of polyethene


  Plastic bags
• How Addition Polymerisation is carried


  • 200°C & very high pressure

  -Usually used to prepare branched polymer chains

  OR

  • Catalysts such as TiCl₃ and Al(C₂H₅)Cl and 60°C

  -The most common production method for non-branched poly(ethene)
• Addition Polymerisation PVC

  
• Addition Polymerisation Examples

  
• Advantages & Disadvantages of Polymers

  ✓ Many uses (e.g. clothing)

  ✓ Recycle

  ✓ Cheap

  ✓ Durable

  ✗ Non-biodegradable

  ✗ Toxic HCl (if it contains chlorine)

  ✗ Greenhouse gases (when burnt)
• Problems + Solutions to using Polymers


  • Separation and Recycling: Using Polymer identification codes
  • Use as a Fuel Source: Burn (combust) under controlled conditions to produce heat energy. Toxic waste products (e.g. HCl) are removed using gas scrubbers for halogenated polymers. For HCl the gas scrub would contain a base to neutralise
  • Feedstock Recycling: Convert Polymers into synthesis gas (hydrogen and carbon monoxide) and use as feedstock for conversion into useful products
  • Develop Biodegradable Polymers: Derived from renewable raw materials (e.g. starch, maize, cellulose)
• C-Cl bond permanent dipole 


  Cl is more electronegative than C & can pull bonding pair of electrons closer towards it
• Why does Electronegativity of Halogens Decrease Down Group 7?


  • Nuclear charge increases but
  • Larger atomic radius
  • Shielding increases
  • Weaker nuclear attraction for bonding pair of e-