chem module 4

• markownikoff's rule


  in electrophilic addition to alkenes the major is formed via the more stable carbocation
• hydration

  • reagent: steam (330 degrees celsius)
  • conditions: high pressure and catalyst - phosphoric acid
  • product: alcohol
• alcohols -> carboxylic acid

  • oxidation
  • potassium dichromate
  • reflux
• alcohols -> aldehydes

  • oxidation
  • potassium dichromate
  • distillation
  • alcohol reacts with oxidising agent [O]
• alcohols (secondary) -> ketones

  • oxidation
  • potassium dichromate
  • heat
• • ketone: -one (propanone)
  • aldehyde: -al (propanal)
• tollen's reagent

  • contains Ag(NH3)2 ions reduced to silver mirror as it oxidises aldehyde to carboxylic acid
  • reaction used as simple test to distinguish aldehydes from ketones
• Tollen's reagent

  • contains Ag(NH3)2 ions - are reduced to silver mirror as it oxidises aldehyde to carboxylic acid
  • reaction is used as simple test to distinguish aldehydes from ketones
• Fehling's solution

  • blue solution (contains Cu2+ ions) are reduced to a red-orange precipitate of Cu2O as it oxidises aldehyde to carboxylic acid
  • reaction is used as simple test to distinguish aldehydes from ketones
• greater branching: less surface contact = less temporary - induced dipoles
• free radical substituition

  • initiation: Cl2 -> 2Cl. and UV
  • propogation: Cl. + CH4 -> HCl + .CH3 (stage 1)
  • (stage 2) CH3 + Cl2 -> CH3Cl + Cl.
  • termination: Cl. + Cl. -> Cl2
  • CH3. + Cl. -> CH3Cl
  • CH3. + CH3. -> C2H6
• overall equation: free radical substituition


  all reactants -> all products (from propagation step)

  • can be cancelled out from both sides
• non-polar molecules

  • symmetrical molecules will have a regular shape and central atom will have the same group attached at each bond. This means the molecule is non-polar.
• polar

  • unsymmetrical
• alkanes -> alkenes

  • hydrogenation
  • 150 degrees celsius
  • nickel catalyst
• mechanisms

  • alkenes = electrophilic addition
  • alkanes = free radical substituition
  • haloalkanes = nucleophilic substituition
• curly arrows


  movement of a pair of electrons
• stereoisomers


  organic compounds with same molecular formula and structural formula but having different arrangements of atoms in space
• structural isomers 


  compounds with same molecular formula but different structural formula
• priority


  I>Br>Cl>F>C>H
• hydrolysis of haloalkanes conditions

  • reagent: aqueous sodium hydroxide
  • conditions: reflux (heat) in aqueous solution
  • product: alcohol
  • nucleophile: hydroxide ion (OH-)
• nucleophiles

  • possess at least one lone pair
  • dont have to possess a negative charge
  • attracted to slightly positive carbon
• alkanes

  • alkanes are saturated hydrocarbons - have single (sigma) carbon-carbon bonds and carbon hydrogen bonds
  • carbons make 4 bonds - tetrahedral shape - bond angle 109.5
  • each orbital of carbon overlaps with orbital of hydrogen atom to form C-H sigma bond
• sigma bond


  overlap of orbitals between two atoms - free to rotate
• branched alkanes

  • straight chains can get closer together
  • straight chains have more surface contact between molecules giving more induced dipole forces
  • these require more energy to break them so boiling point is higher
  • boiling point decreases with more branching
• stereoisomers in alkenes

  • occurs due to restricted rotation of C=C bonds
  • occurs if each carbon in double bond has 2 different groups attached.
• • Cis: groups/atoms are on same side of double bond
  • trans: groups/atoms on opposite sides across double bond
• cahn-inggol-prelog (cip) rule

  • Z higher priority atoms on same side of c=c bond
  • E higher priority atoms on opposite sides of c=c bond
  • priority: I>Br>Cl>F>C>H
• complete combustion of methane

  CH4 + 2O2 -> CO2 + 2H2O
• incomplete combustion of methane 


  4CH4 +5O2 -> 2CO + 8H2O +2C
• reactivity of alkanes

  • alkanes have low reactivity with many reagents because:
  • have high bond enthalpy (strong bonds)
  • low polarity of sigma bonds present
• heterolytic fission


  happens when each bonding atom receives one electron from the bonded pair - forming two radicals
• homolytic fission


  happens when one bonding atom recieves both electrons from the bonding pair
• average bond enthalpy 


  mean energy needed for 1 mole of a given type of gaseous bonds to undergo homolytic fission
• properties of alkenes

  • insoluble in water and less dense than water
  • non-polar compounds
  • range of physical states
  • Bp/Mp increases with more C
  • Bp/Mp lower than equivalent alkane
• pi bond


  two 2p orbitals overlap to form second bond known as pi bond
• aliphatic compounds


  carbon atoms joined together as straight chains or branched chains
• alicyclic compounds


  carbon atoms joined together in a ring structure (not aromatic)
• aromatic compound


  at least one benzene ring in structure
• position isomers 


  differing position of the same functional group in the molecule