Halogenoalkenes

  • Created by: elliee02
  • Created on: 23-03-19 15:12
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  • HALOGENO ALKANES
    • NAMING
      • Bromo-   (Br)
      • Chloro-   (Cl)
      • Iodo-   (I)
      • Primary - halogen attached to carbon which is attached to 2 H and 1 Alkyl group
      • Secondary - halogen attached to Carbon which is attched to 1 H and 2 Alkyl groups
      • Tertiary - Halogen attached to Carbon whicb is attached to 3 Alkyl groups
    • INVESTIGATING RATE OF HYDROLYSIS
      • OF CHLORO, BROMO AND IODO
        • Conditions; warm with aq silver nitrate solution in ethanol
        • Iodoalkane forms quickest then bromoalkane then chloroalkane
          • C-I bond is weakest so requires less energy to break bond so rate of reaction is quickest
          • C-Cl bond is strongest and so requires more energy to break bond so rate of reaction is slowest
          • Rate is not determined by size of dipole as otherwise the trend would be opposite to the one observed
        • Ethanol is used as a co-solvent to mix the AgNO3 and X-alkane mix
        • Draw a cross on the back of 3 test tubes. Add HALOALK into test tube with silver nitrate and ethanol. Put in test tube stand. Start stopwatch. Time how long it takes for cross to disapear
        • Fair test
          • Same vol of all substances
          • use same water bath at same time to keep temp constant
      • OF PRIMARY, SECONDARY AND TERTIARY
        • E.g 1-bromobutane, 2-bromobutane and 2-bromo-2methylbutane
        • Tertiary fastest then secondary then primary slowest
          • Tertiary react via SN1 (substitution nucleophilic bimolecular) reaction pathway, which is a quicker mechanism
            • Tertiary can't react via SN2 as the steric hindrance of the Alkyl groups prevent the nucleophile from attacking the central Carbon s+
          • Primary HALOALK cannot react via SN1 because the primary carbocations are not stable enough to form in the first step
          • Secondary HALOALK react via via an intermediate mechanism - draw either SN1 or SN2
        • React each HALOALK with silver nitrate solution in the presence of ethanol in a water bath. Record time fore precipitate to obscure a cross
    • Nucleophile - species which attacks a region of S+ by donating a lone pair of electrons to form a dative covalent bond
    • Reaction with Aq silver nitrate in ethanol
      • water acts as nucleophile
      • Warm with aq ailver nitrate and ethanol
      • alcohol formed, H+ ion and halide ion then silverhalogen formed
      • Nucleophilic substitution
      • substitution
    • Reaction with potassium cyanide, KCN
      • Heat with potassium cyanide
      • Lengthens Carbon chain
      • Substitution
      • Nucleophilic substitution
      • Nucleophile is c=N (triple bond)
      • Nitrile formed
    • Reaction with Ammonia, NH3
      • Heat with ammonia solution
      • Substitution
      • Nucleophilic substitution
      • Amine formed
    • Reaction with Aq potassium hydroxide, KOH
      • Alcohol and ion formed
      • Nuclophilic substitution
      • Substitution
      • Heat under reflux with aq potassium hydroxide solution
    • Reaction with potassium hydroxide in ethanol
      • Heat with KOH dissolved in ethanol
      • Eliminatin
      • Alkene formed
      • Alkene, hydride ion and water formed
    • In exam, draw either SN1 or SN2
  • Reaction with Aq potassium hydroxide, KOH
    • Alcohol and ion formed
    • Nuclophilic substitution
    • Substitution
    • Heat under reflux with aq potassium hydroxide solution

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