AQA Chemistry Unit 4 Organic

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Aldehydes & Ketones

  • Functional group C=O(carbonyl group).
    • Aldehydes the carbonylgroup is on the last carbon, 
    • Ketones the carbonyl group is between two other carbons.
  • You can distinguish between Aldehydes and Ketones by using Tollens reagent or Fehlings solution.
    • Tollens: silver mirror with Aldehydes, no change with Ketones
    • Fehlings: colour change from blue to brick red with aldehydes, no change with Ketones.
  • Aldehydes reduced to primary Alcohols and Ketones to secondary Alcohols.(reagents: NaBH4,H-, [H]).

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  • Aldehydes go through nucleophilic addition, e.g. with Hydrogen cyanide (HCN)
    • This reaction is not done in a lab as cyanide is highly toxic.

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  • Aldehydes are oxidised to form Carboxylic acids.
    • Oxidising agents: acidified Potasium dichromate with dilute sulphuric acid.
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Carboxylic Acids

  • Functional group COOH.
  • They are weak acids, but will liberate CO2 from carbonates.
  • Will go through Addition-Eliminatin reactions with Alcohols to form Esters in the presence of a strong catalyst(H+).

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  • long chain Carboxylic acids(fatty acids) can be hydrolysed from vegetable oils and animal fats, along with soap and glycerol.
  • long chain carboxylic acid along with methyl esters make up biodiesel.
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Esters

  • Functional group RCOOR'
  • Esters have very pleasent smells.
  • Esters can be hydrolysed to form a Carboxylic Acid and an Alcohol.

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  • Biodiesel is made up of methyl esters alond with long chain carboxylic acids.

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  • Common uses:
    • plasticizers
    • solvents
    • perfumes
    • food flavorings
  • Animal fats and vegetable oils are Esters of glycerol(propane-1,2,3-triol).
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Acylation (Acid Derivatives)

  • Acid Chlorides, functional group RCOCl
    • go through nucleophilic addition-elimination reactions.

Acid Chloride and Ammonia                                                    Acid Chloride and amine    

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Acid Chloride and Alcohol                                                      Acid Chloride and Water

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  • Acid Anhydrides, functional group RCOOCOR'

                           Ammonia(NH3)                  Amide(R'-NH2)                    Alcohol(R'-OH)                Water(H2O)

Anhydride                      

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Aromatic Chemistry (Arenes e.g. Benzene)

  • Benzene has a pi system(a ring of delocalised electrons).This means that Benzene is more stable than if it has three alternating C=C double bonds.
    • Evidence for this:
    • therefore with three double bond the enthalpy expected would be 3x bigger.
    • The enthalpy is in fact smaller than expected and therefore more stable.
  • Arenes undergo electrophilic substitution. This can be seen with a nitronium ion. This nitration is also the basis of the synthesis of TNT.
    • HNO2 --> NO2+ +OH-

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  • Friedel-Crafts acylationreactions are useful in the synthesis of new substituted aromatic compounds. They use an Aluminium chloride catalyst and an RCO substitute. 
    • RCOCl(Acyl chloride) + AlCl3 --> RCO+ + AlCl4 - 

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  • The Aluminium Chloride is reformed by reacting with a H+ ion: AlCl4 - + H+ --> AlCl3 + HCl
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Amines

  • Amines are Bronstead-Lowery bases.
    • some amines are stronger bases than others, primary amine>ammonia>phenylamine
      • This is because of the inductive effect, electron from alkyl groups are attracted towards the nitrogen, this increases the electron density on the nitrogen, making it a better electron pair donor. Aryl groups withdraw electrons from the nitrogen and are worse electron pair donor.
  • Amine form salts when reacted with acids
    • e.g. C2H5NH2(ethylamine) + HCl --> C2H5NH3+ + Cl-
  • Amines undergo nucleophilic substitution with a haloalkane.

haloalkane and ammonia                                     haloalkane and primary amine

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  • Amines are prepared from the reduction of nitriles. 
    • RBr + CN- --> R-C=N + Br- , R-C=N + 2H2 --> R-CH2NH2       
  • Aromatic amine are prepared from the reduction of nitro compounds.
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Amino Acids

  • Amino Acid have both acid and base properties as they can form zwitter ions.

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  • proteins are formed from polymers of amino acids joined by peptide links. peptide links are formed by the condensation of two amino acids, the peptide bond can be broken through hydrolysis.
  • A mixture of Amino Acids can be separated by chromatography.
  • In acidic conditions the lone pair on the amine group accepts a proton to form a positive ion. It has been Protonated

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  • In Alkaline conditions the OH group loses a proton (H+ ion) and is deprotonated.

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  • Amino Acids can form H-bonds with each other, this is that keeps a protein in a helical structure.
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Simple Tests for Functional Groups

  • Alkenes test = Bromine water
    • orange-brown water goes clear in the presence of an alkene
  • Carboxylic acids test = NaHCO3 or Universal indicator
    • CO2 gas produced, turns limewater cloudy or turns ornage
  • Alcohols test = potassium dichromate or potassium manganate 
    • with primary & secondary alcohols: Orange solution to green solution or Purple solution to colourless solution, with tertiary alcohols: no change
  • Acyl Chlorides test = silver nitrate (AgNO3)
    • vigorous fuming reaction, white precipitate of AgCl formed.
  • Haloalkanes test = Haloalkane warmed with ethanol and added to silver nitrate.
    • chloro - white precipitate (goes colourless in dilute ammonia)
    • Bromo - Cream Precititate (goes colourless in concentrated ammonia)
    • Iodo - Yellow Precipitate (no change with concentrated ammonia)
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