Chem 4 More organic chemistry

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  • More Organic Chemistry
    • Aromatics
      • Derived from Benzene
      • C6H6
      • The Kekule Model
        • Ring of C atoms with alternating single and double bonds
        • Flips between two forms
        • Wrong because all the bonds are the same length
        • says that there should be 3 short double bonds and 3 longer single bonds
      • Delocalised Model
        • Each C donates an electron from its p-orbital
          • These form a ring of delocalised electrons
        • More stable than the Kekule model
          • shown by the experimental enthalpy of hydrogenation
      • Electrophilic Substitution Reactions
        • Has a ring of high density electrons so attracts electrophiles
        • Friedel Crafts
          • Forms a carbocation from an Acyl-chloride and AlCl3
            • electrons in the benzene ring are attracted to the carbocation
              • two electrons bond with the cation and partially breaks the delocalised ring and gives it a positive charge
                • the AlCl4+ ion is attracted to the hydrogen and removes it from the benzene, allowing the catalyst to reform.
          • needs to be heated under reflux, in a non aqueous-environment for the reaction to occur
        • Nitration
          • warm benzene with conc. nitric acid to form nitrobenzene
            • the nitronium ion attacks the benzene ring
              • an unstable intermediate forms and H+ is lost in order to restablise it
          • useful because nitro compounds can be reduced to form aromatic amines, used to manufacture dyes and drugs
            • nitro compounds decompose violently when heated so are used to make explosives
    • Amines
      • organic derivatives of ammonia
      • Quarternary Ammonium Salt N(CH3)4+
        • used as surfactants, e.g.in hair products and fabric conditioners
          • the + charge binds to negatively charged surfaces like hair and fibre to reduce static
      • has a lone pair of electrons that can form dative covalent bonds
      • Strengths of amines
        • the more available the lone pair the stronger the base
          • alkyl groups push the electrons into the middle, increasing the lectron density of the N so making the lone pair more available
            • a benzene ring draw the electrons towards itself, the electron density of the N decreases so the lone pair is much less available
      • Aliphatic Enzymes are made from Haloalkanes or Nitriles
        • You can heat a Haloalkane with an excess of ammonia
          • a mixture of primary secondary and tertiary amines and quaternary salts is produced
            • the products can be separated   using fractional distillation
        • Or you can reduce a Nitrile
          • using LiAlH4 (a strong reducing agent) followed by a weak acid
            • another way is to reflux the nitrile with sodium and ethanol
          • LiAlH4 and sodium are too expensive for industrial use
            • industry uses a metal catalyst like Nickel or Platinum at a high temp and pressure
              • its called catalytic hydrogenation
        • Aromatic Enzymes are made by reducing a nitro compound
          • 1. heat an mixture of a nitro compound, tin metal and conc. HCl under reflux to make a salt
            • add NaOH to make it an aromatic amine
    • Amino Acids and Proteins
      • have an amino group and a carboxyl group
        • they are chiral molecules so one enantiomer will rotate polarised light
      • can exist as Zwitterions
        • these have  a positive and negative charge on the molcule
        • at the isoelectric point (the pH where the overall charge is zero) it forms a zwitterion
          • under more acidic conditions the -NH2 group becomes protonated to become -NH3+
          • under more basic conditions the COOH group is likely to loose a proton to become COO-
      • Paper Chromatography is used to seperate out a mixture of amino acids
      • Proteins are condensation polymers of amino acids
        • -CONH- group shows the peptide link
        • Hydrogen bonds keep protein molecules in shape
    • Polymers
      • addition polymers are formed from alkenes
      • Condensation polymers include polyamides, polyesters and polypeptides
        • Polyamides are made from dicarboxylic acids and diamines
          • Functional group -CONH-
          • Nylon 66 is made form 1,6-diaminohexane and hexanedioic acid
          • kevlar is made from benzene-1,4-diamine and benzene-1,4-dicarboxylic acid
        • Polyesters are made from dicarboxylic acids and diols
          • forms an ester link -COOC-
          • Terylene (PET) is made form benzene-1,4-dicarboxylic acid and ethane-1,2-diol
      • Disposal
        • Addition polymers are non-biodegradable
        • Condensation polymers can be decomposed by hydrolysis, so are biodegradable but the process is very slow
        • waste plastics can be buried recycled or burnt
          • landfill is cheap and easy but requires vast areas of land and produces methane and leaks can contaminate water supplies
          • Burning them can produce heat to supply electricity
            • however some polymers contain things like chlorine that is toxic when released
              • passing the gas through scrubbers can nuetralise gases like HCl but CO2 produced is a greenhouse gas
          • recycling is costly and requires a lot of manpower, but solves the problem of finite oil supplies
          • Environmental Pressures change the way we use plastics, e.g. trying to use them less in packaging.
  • Addition polymers are non-biodegradable

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