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ORGANIC REACTIONS

ORGANIC REACTIONS. Types of Reactions. Substitution: Polar Non-polar. Rearrangement. Definitions. Mechanism: Complete step-by-step of exactly which bonds break and which bonds form and in what order.

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ORGANIC REACTIONS

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  1. ORGANIC REACTIONS Dr Seemal Jelani

  2. Types of Reactions • Substitution: • Polar • Non-polar Dr Seemal Jelani

  3. Rearrangement Dr Seemal Jelani

  4. Definitions • Mechanism: Complete step-by-step of exactly which bonds break and which bonds form and in what order. • Thermodynamics: The study of the energy changes that occur in chemical transformations. This allows for comparison of stability of reactants and products. • Kinetics: The study of reaction rates, determining which products are formed most rapidly. One can predict how the rate will change with changing conditions. Dr Seemal Jelani

  5. Reaction Profile (Exothermic) Dr Seemal Jelani

  6. 2nd Order Reaction Dr Seemal Jelani

  7. 1st Order Reaction Dr Seemal Jelani

  8. Bond Breaking:Non-polar and Polar Dr Seemal Jelani

  9. Bond Forming:Non-polar and Polar Dr Seemal Jelani

  10. Non-polar Reaction Involves Free Radicals Dr Seemal Jelani

  11. Free Radicals are Neutral, but Electron-Deficient Dr Seemal Jelani

  12. Free Radical Chlorination Dr Seemal Jelani

  13. Experimental Evidence Helps to Determine Mechanism • Chlorination does not occur at room temperature in the dark. • The most effective wavelength of light is blue that is strongly absorbed by Cl2 gas. • The light-initiated reaction has a high quantum yield (many molecules of product are formed from each photon of light). Dr Seemal Jelani

  14. Free Radical Species are Constantly Generated Throughout the ReactionPropagation Dr Seemal Jelani

  15. Termination: Reaction of any 2 Radicals Dr Seemal Jelani

  16. Enthalpy • It is the change that occurs in a system when one mole of matter is transformed by a chemical reaction under standard conditions Bond Dissociation Energy • the amount of energy which is required to homolytically fracture a chemical bond Dr Seemal Jelani

  17. Enthalpy of Reaction (DHo) Measures Difference in Strength of Bonds Broken and Bonds FormedBond Dissociation Energy Dr Seemal Jelani

  18. DHo = Sbonds broken-Sbonds formed Dr Seemal Jelani

  19. Dr Seemal Jelani

  20. Chlorination of Propane Dr Seemal Jelani

  21. Chlorinationof Methylpropane Dr Seemal Jelani

  22. 3o Radicals are Easiest to Form Dr Seemal Jelani

  23. Stability of Free Radicals Dr Seemal Jelani

  24. Chlorofluorocarbons and the Depletion of Ozone Dr Seemal Jelani

  25. Polar ReactionsNucleophilic substitution reaction • Theme One Nucleophile is substituted for another nucleophile • General reaction Dr Seemal Jelani

  26. DEFINITION OF A NUCLEOPHILE • A species that loves a nucleus • Since nuclei are positively charged, so nucleophiles are negatively charged or bear a partial negative charge • Examples are lone pairs or a hydroxide ion. • Nucleophile is an electron rich species. Dr Seemal Jelani

  27. ELECTROPHILES • An ion or molecule that is electron deficient and can accept electrons • Electrophiles are often reducing agents and Lewis acids • They are either positive ions (e.g. NO2+) or Dr Seemal Jelani

  28. molecules that have a positive charge on a particular atom(e.g. SO3, which has an electron-deficient sulphur atom) • In organic reactions they tend to attack negatively charged parts of a molecule Dr Seemal Jelani

  29. CLASSIFICATION OF NUCLEOPHILIC • Nucleophiles can be classified according to the kind of atom that forms a new covalent bond. 1. Oxygen Nucleophile (HO-, CH3O) 2. Nitrogen Nucleophiles (NH3, RNH2…) Dr Seemal Jelani

  30. 3 Sulfur Nucleophiles (HS-, RS- …) 4 Halogen Nucleophiles (I-..) Dr Seemal Jelani

  31. Polar Reactions:Nucleophiles & Electrophiles Dr Seemal Jelani

  32. Dr Seemal Jelani

  33. Nucleophiles are BasesElectrophiles are Acids Dr Seemal Jelani

  34. Addition of HBr to Ethylene Dr Seemal Jelani

  35. DGo = DHo - TDSo Dr Seemal Jelani

  36. Reactions Often Go Through Intermediates Dr Seemal Jelani

  37. Transition State Dr Seemal Jelani

  38. Addition Reaction is a Two-Step Mechanism Dr Seemal Jelani

  39. How Many Mechanistic Steps?How Many Intermediates?How Many Transition States?Which Step is Rate-Determining? Dr Seemal Jelani

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