Paper 2

• CC-sigma bond


  Formed by the end-to-end or direct overlap between two orbitals
• CC-pi bond


  Formed by the side-to-side overlap between two p-orbitals
• Drawing a diagram to label the CC-sigma and CC-pi bonds


  Helps give something to talk about
• E/Z isomerism


  Compares the relative positions of priority groups on a double bond

  • Z = priority group Zame side
  • E = piority group opposite side
• Cis/trans isomerism


  Compares the relative positions of identical groups on a double bond

  • Cis = identical group same side (Sisters)
  • Trans = identical group opposite side
• Drawing a diagram based on an ethane molecule


  Makes it easier to show the relative positions of the groups
• Major and minor products

  When an alkene is unsymmetrical and something like H2O, HX or hydrogen halide gas is added, the major product forms from the most stable carbocation intermediate

  • major products has the most Carbons attached to it compared to the minor product
• Stability of carbocations


  • Tertiary > secondary > primary
• Purifying an organic liquid


  1. After reaction is complete, pour mixture into separating funnel
  2. Neutralise excess acid using Sodium Carbonate (stops bubbling when all gone), then allow 2 layers to settle
  3. Use density infor to establish layers / if its not given add water to establish the aqueous layer as it will get bigger
  4. Collect desired layer, add drying agent (CaCl2) to remove traces of water in the organic layer
  5. Distil the dried product and collect fraction that comes over the at the boiling point of the organic liquid boiling point
• Determining purity of organic liquid


  • Check boiling point matches known data, boils over a narrow range
  • Run TLC, measure Rf value & compare to known data / run tlc and compare to the chromatogram of a pure sample
  • Run NMR/IR/Mass spectrum compare to spectral database of pure compounds
• Purifying an organic solid


  1. Purify by recrystallisation
  2. Dissolve in minimum hot solvent
  3. Cool in ice to recrystallise (impurities stay in solution)
  4. Filter using reduced pressure filtration
  5. Wash with cold solvent then dry
• Determining purity of organic solid

  1. Measure melting point and compare to known value
  2. run TLC, measure rF value, compare to known data / run TLC and compare to chromatogram of pure sample
  3. Run NMR/IR/Mass Spectrum and compare to known spectral data of pure compounds
• Drawing apparatus for reflux


  Flask with chemicals, heat source, condenser with water flow in at bottom, out at top
• Drawing apparatus for distillation

  Flask with chemicals, heat source, thermometer, condenser with water flow in at bottom, out at top, collect distillate
• Drawing apparatus for filtering under reduced pressure

  Buchner flask connected to vacuum, Buchner funnel with filter paper
• Drawing apparatus for separating funnel


  Funnel-shaped apparatus, higher density liquid on bottom, lower density on top
• Ozone levels were relatively stable until the 1940s due to a dynamic equilibrium in the stratosphere

  • O2 +O ⇌ 03 rate of formation of Ozone = rate of breaking down UV
  • Stratospheric ozone can absorb harmful UV from sun
• • CFCs can lead to ozone depletion
  • CFCs stable due to high bond enthalpies so not broken down in lower atmosphere
  • CFCs reach stratosphere where broken down by UV light
• Free radical Substitution Reaction of CFCs in the Stratosphere

  INITIATION:

  CCl3F -> Cl* + CCl2F* homolytic fission of C-Cl bond (C-F)

  PROPAGATION:

  O3 + Cl* -> O2 + ClO*

  ClO* + O -> O2 + Cl*

  OVERALL:

  03 + O -> 2O2 ozone being broken down irreversibly, catalysed by Cl*
• Evidence against Kekules modefor Benzene

  • All bond lengths are the same (intermediate between single and double carbon bonds)
  • Enthalpy change of hydrOGENation is less exothermic than expected
  • It is resistant to reactions so it needs a catalyst
• Phenol 


  • Weak acid that reacts with strong bases like NaOH, but too weak to react with Na2CO3 producing no bubbles of CO2
  • reacts with Br without catalyst -> 2,4, 6 - tribromophenol
  • Br decolourises and forms white ppt
  • Reacts with HNO3 without catalyst at RT
• Reactivity - benzene vs phenol

  
  

  BASED ON PI ELECTRONS!!!

  • Benzene has delocalised pi bonds wheras in phenols a lone pair of electrons form the OH group is delocalised into the ring
  • Benzene has a lower electron density than phenols
  • Benzene is unable to polarise electrophiles so it cant attract them strongly whereas phenols can polarise electophiles and attract them stongly
• Reactivity - Benzene vs Alkene

  BASED ON PI ELECTRINS!!!

  • Benzene has delocalised pi electrons whereas in alkenes it had localised C=C bonds
  • Benzene has a lower pi electron density than alkenes
  • Benzene is unable to polarise electrophiles so cant attract them strongly whereas alkenes are able to polarise electrophiles and can attract them strongly
• Directing groups

  • -OH & -NH2 = electron donating, increases electron density in DROPE, more reactive towards electrophiles, direct position of substitutions at 2 & 4 on benzene ring
  • NO2 = electron withdrawing, decreases electron density in DROPE, less reactive towards electrophiles, directs position of substitutions at 3
• Amines

  • Acts as bases - accept H+ using lone pairs on N (coordinate bond) -> Ammonium salts
  • Primary ALIPHATIC amines made from reacting haloalkane with excess ammonia in ethanol
  • Excess ammonia avoids further substitutions to secondary and tertiary amines. if the haloalkane is in excess the lone pair on the N of the primary amine it will attack another haloalkane to make a secondary amine etc
  • Aromatic Amines made by reducing nitroarenes using tin and conc HCl
  • Amines also made by reducing nitriles using H2/Ni catalyst
• Carbon - Carbon bond formation:

  • Seein in nitriles/hydroxynitriles, alkylation and acylation of benzene
  • Haloalkane + CN- + ethanol -> nitriles (nucleophilic substitution)
  • Carbonyls + CN- + H2SO4 (makes HCN in situ) -> Hydroxynitriles (nucleophilic addition)
• Thin layer chromatography (TLC)


  • seperation by relative ADSORPtion
  • Rf = distance travelled by spot / distance traveled by solvent
  • Compare Rf values to know data values
• Gas Chromatography (GC)


  • Separation by relative ADSOPtion if the staitionary phase is solid
  • Separation by relative solubility if staitionary phase is liquid
  • Retention times (time from injection to detection)
  • Compare retention time to known data
  • Areas under peak = relative amounts of components in sample
  • Actual concentrations found by measuring area under curve for known concentrations then plotting a calibration curve
• Tests for organic functional groups

  • Measures mass: charge (m/z)
  • + on formulae
  • Significant peak on furthest right = molecular ion peak = Mr of molecule
  • Fragement peaks caused by breaking one covalent bond in the molecular ion
  • e.g m/z = 15 [CH3]+, m/z = 29 [C2H6]+
• Classification of Organic Compounds

  • Hydrocarbon - contains Carbon and Hydrogen ONLY
  • Saturated - C-C bonds ONLY
  • Unsaturated - C=C/ C≡C / aromatic (benzene) ring
  • Aliphatic - Straight chains, branched chains, non-aromatic rings
  • Aromatic - Contains one or more benzene ring
  • Alicyclic - Ring but not aromatic (benzene) ring
• Boiling Points

  • No branching/ long, straight chain = more surface contact, more induced dipole-dipole forces, more energy needed to overcome the forces, boiling point increase
  • Branching = less surface contact, weakened induced dipole-dipole forces, less energy needed to overcome forces, lower boiling point
• Complete combustion of alkanes

  • C4H10 + 6.5O2 -> 4CO2 + 5H2O
  • used as fuel to make energy for vehicles