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Organic Chemical Reactions

Organic Chemical Reactions. You will learn the different types of organic reactions you need to know like electrophilic addition, free radical substitution, nucleophilic substitution and elimination, hydrolysis, reduction, oxidation and polymerisation. Electrophilic substitution.

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Organic Chemical Reactions

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  1. Organic Chemical Reactions You will learn the different types of organic reactions you need to know like electrophilic addition, free radical substitution, nucleophilic substitution and elimination, hydrolysis, reduction, oxidation and polymerisation

  2. Electrophilic substitution • Ethene reacts with Halogens or sulphuric acid • An electrophile is a positive (relative), species that is attracted towards a negative centre • Which bond on ethene is a very negative centre? • Recall: Addition of bromine to ethene …the test for an alkene • Recall: Addition of steam to make alcohols

  3. Reactions of halogens with ethene • What is the order of reactivity with the halogens? • CH2=CH2 + X2 CH2X=CH2X • Write the equation for bromine and name the product • Brδ+-Brδ- This is an induced dipole, now the Brδ+ is attracted to the π (pi) bond • This is the electrophile • A more stable sigma bond forms and a bromine ion is produced

  4. There is a positive charge on the carbon without the bromine which then attracts the negative bromine ion • H2C=CH2 + Brδ+-Brδ- • H2C+-CH2Br + Br- BrH2C-CH2Br • Result formation of dibromoethane

  5. Hydrogen Halides • The bond strength increases with increasing electronegativity • Predict which will react the fastest HCl/HBr/HI • This time the Hydrogen ion acts as the electrophile as the bond is Hδ+-Brδ- • Hydrogen is the positive or electron deficient, it goes by the same mechanism except there is a permanent dipole not induced which will have what effect on the rate?

  6. Sulphuric acid catalysed reactions with ethene • H2C=CH2 + δ+H-Oδ-SO3H H2C+-CH2H + HSO4- • H3C-H2Cδ+-O δ-SO3H + H2O CH3CH2OH + H2SO4 • Why does the oxygen of water attack the positive centre?

  7. Nucleophilic Substitution • A nucleophile: A species that donates a pair of electrons to a electron deficient atom in order to form a covalent bond • Species in ammonia, hydroxide and cyanide ions • Species that are attacked: Compounds that have electronegative elements bonded to carbons. E.g. haloalkanes like 1-bromomethane • Products made = usually alcohols or amines

  8. Name some substances that have lone pairs of electrons • H3CH2Cδ+Brδ- + ÖH- • H3C-H2COH + Br - • What conditions are best for this? Find out. • Weak base, water solvent and low temperature

  9. Nucleophilic Elimination • The formation of alkenes from haloalkanes • H3CH2Cδ+Brδ- + ÖH- • H3C-H2COH + Br -

  10. H ÖH- C C Br What alkene will be produced? Ethene and a bromide ion Mechanism

  11. Conditions

  12. Free Radical Substitution • The reaction between chlorine and alkanes (with UV light) • What are the products of this reaction? • What is the mechanism? Find out

  13. 2 • Chlorine UV light 2 Chlorine radicals • What is a radical? Define it. • Why are they so reactive? • What do steal off other atoms? • What substances would be likely to form radicals?

  14. Find out the mechanism of how a free radical reaction is started, carries on the chain reaction and ends • 3 step reaction: • Initiation • Molecular bond is broken, represented • Cl2 2Cl. • Cl-Cl

  15. This called homolytic fission, write a definition for this • This means that both atoms in the bond get 1 electron each • Opposite is called heterolytic fission, you know this what is this process? • Hetero and homo

  16. Propagation The radical reacts with other reactant. Cl.+ CH4 HCl + .CH3 H3 C. + ??? Write down what the products are if it collides with Cl2 or CH4

  17. Termination • What must happen for the reaction to stop? • How can you get rid of the radicals? • H3 C. + Cl. CH3Cl • What other termination products could be formed? • Reactions that this happens in: • Thermal Cracking • Alkane halogenation

  18. Esterification is reversible This reaction to make an ester is called condensation as water is produced To break up an ester is called hydrolysis as it uses water Hydrolysis

  19. Reduction and oxidation • Write down the different types of oxidation • Write down the different types of reduction • Mn7+ + 5 e- Mn2+ • Is this oxidation or reduction? • Mg(s) + Fe2+(aq) Fe(s) + Mg2+(aq) • What is this called? • CH2CH2 K2Cr2O7 CH2OHCH2OH • What is the species and process called? • Alcohols into ketones and aldehydes (and carboxylic acids when done further)

  20. Polymerisation • What does this mean? • Name some natural and synthetic polymers. • What is the difference between addition and condensation polymerisation, find out. • What types of molecules take part in this reaction? List them. • What do they have in common?

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