Organic

• When measuring loss of gas, why is a conical flask better than a beaker?


  reduce loss of liquid droplets
• Why is chloroethanoic acid stronger than ethanoic acid?

  Chlorine is a electron withdrawing group, increase polarity of O-H bonds
• 


  Optical isomers because C+ planar, chiral carbon and are non superimposable mirror images, so they can be attacked from above or below
• Slowest step - rate determining step depends on rates equation, number of atoms used
• Alkenes, double carbon bonds so have highly electron dense, vulnerable to attacks by electrophiles.
• E-Z isomerism arises when there are restricted rotation around the C=C bond and when there are two different groups attached to both ends pf the double bond.
• Electrophile


  an electron pair acceptor
• Electrophilic addition because alkenes have areas that are highly electron dense and attracts electrophiles.

  • Br2 approaches, pi bond electrons repel the electron pair in Br-Br and induces a dipole, Br2 becomes polar and electrophilic
  • HBr is polar because Br is more negative so H is attracted to the electron rich pi bonds
• Unsymmetrical leads to isomeric products
• In electrophilic addition, major product is formed via more stable carbocation intermediate. More stable carbocation intermediate because methyl groups on either sides are electron releasing and reduce the charge on the ion and stabilises it
• alkenes are planar 120 degrees
• Bond angles in alcohol, 109.5 and 104.5 because H-O-C has 2 bonding pairs and 2 lone pairs repels and try to get as far apart as possible. Lone pairs repels more than bonding pairs so bond angle reduced
• Electron pairs repels equally and try to get as far apart as possible. if there are no lone pairs, electron pairs repel equally. If there are lone pairs, the repel more than electron pairs and so reduce bond angle
• The alcohols have relatively low volatility and high boiling points due to their ability to form hydrogen bond between alcohol molecules. Smaller alcohols can dissolve in water because they can form hydrogen bonds to water molecules.
• Partial oxidation of alcohols

  • reagent = acidified (dilute sulfuric acid) potassium dichromate
  • warm distil
• Distillation - separation technique to separate organic product from reacting mixture. To maximise yield, collect distillate at approximate boiling point not higher. cool collection flask in ice can also increase yield
• distillation used for collecting aldehydes immediately after aldehyde has formed to prevent further oxidation. electric heaters used because organic chemicals are highly flammable. Water enters from the lowest point to go against gravity for effective cooling and prevents back flow of water
• Full oxidation

  • reagent: distilled sulfuric acid and potassium dichromate
  • conditions: excess potassium dichromate. Heat under reflux
• Reflux is used when heating organic reaction mixture for a long periods. Condenser prevents them from escaping by condensing them back into liquid.

  • never seal the end of condenser, build up of gas can cause apparatus to explode
  • Anti-bumping granules added to prevent vigorous and uneven boiling by making small bubbles
• Only aldehydes can be oxidised by fehling's solution and Tollen's reagent
• Fehling's solution - blue then red precipitate if aldehyde present. No reaction for ketone
• Tollen's reagent - silver mirror if ketone present. No reaction for ketone
• Carboxylic acid test by adding sodium carbonate. Fizzing and effervescence, CO2 gas produced
• Fermentation

  • glucose -> ethanol + co2
  • yeast, anaerobic, 30-40 degrees
• Advantages to fermentation


  • renewable
  • low level equipment, cheap
• disadvantages to fermentation

  • batch process, slow, high production costs
  • not pure, need purifying by fractional distillation
• Hydration of ethene to form alcohol

  • high pressure 300 degrees
  • high temperature 70 atm
  • strong acidic catalyst H3PO4
• advantages for hydration of ethene

  • faster reaction
  • purer product
  • continuous process (cheaper manpower)
• disadvantage to hydration of ethene

  • expensive equipment
  • ethene is a non-renewable resource
  • high energy costs for pumping to produce high pressure
• Carbon neutral 


  an activity that has no net annual carbon emission to the atmosphere
• Removal of CO2 by photosynthesis

  • 6 CO2 + 6 H2O -> C6H12O6 + 6 O2

  production of CO2 by fermentation and combustion

  • C6H12O6 -> 2 CH3CH2OH + 2 CO2
  • 2 CH3CH2OH + 6O2 -> 4CO2 +6H2O
• why may fermentation not be carbon netral?

  Doesn't include any account of energy needed to irrigate the plant, distillation and processing fuel. If energy from these processes are from fossil fuel then it is not carbon neutral
• Nucleophilic substitution

  • rate of substitution reactions depends on strength of C-X bonds, easier to break, faster the reaction. C-I is fastest and C-F is slowest
• Water is a poor nucleophile but it can react slowly with halogenoalkanes in a substitution reaction.
• Nucleophile - a electron pair donator
• Aqueous conditions for nucleophilic substitution with hydroxide ion is important because solvent might become ethanol and can undergo elimination
• Exception for nucleophilic substitution for tertiary halogenoalkanes

  • Br breaks off first
  • hydroxide ions attacks positive carbon atoms after

  It undergoes this mechanism because the tertiary carbon stabilised by electron releasing methyl groups around it. And because bulky methyl groups prevent nucleophile from attacking
• Aqueous = substitution

  Alcoholic = elimination
• Chloroalkanes and chlorofluoroalkanes can be used as solvents but has been stopped because of toxicity and bad effects for environment
• Ozone is beneficial because it filters out as much of the sun's harmful UV radiation. CFC causes holes to form in the ozone layer