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Tema 1.9 Session1


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Tema 1.9 Session1

  1. 1. Mòdul MD2301 - Formació general; 564497 – Química orgànica i inorgànica MASTER ON DRUGS, COSMETICS AND FOOD QUALITY Dr. Antonio Delgado Universitat de Barcelona October 2009
  2. 2. Thematic bloc: Organic chemistry Functional groups; C-C bond forming reactions; Functional group transformations Organic reactivity Conformational analysis of alkanes and cycloalkanes; chirality; stereochemical descriptors Stereochemistry Chemical bond; hybridization; resonance and aromaticity Structure of organic compounds
  3. 3. Session 1 Basic principles of chemical reactions : Kinetic and thermodynamic processes. Concerted and stepwise processes. Reaction intermediates: radicals and ions (homolytic and hereterolytic bond-breaking processes). Types of organic chemical reactions: substitution, elimination, addition, addition-elimination, oxidation, reduction. Substitution reactions at saturated carbons . Nucleophiles and Electrophiles. Nucleophilic substitution reactions. Alkyl halides as electrophiles. Concerted (SN2) versus stepwise (SN1) processes. Other electrophiles and nucleophiles. Synthetic applications. Elimination reactions . Concerted (E2) versus stepwise (E1) mechanisms. Mechanistic considerations. Competition between SN and E processes. Synthetic applications of the elimination reactions.
  4. 4. “ Communication in Chemistry” Atoms are the alpahabet of chemistry Molecules are the words Reaction mechanisms are the grammar Synthetic sequences are the sentences
  5. 5. Kinetics and thermodynamics of chemical reactions
  6. 6. Kinetic versus thermodynamic control
  7. 7. Concerted mechanism Stepwise mechanism Reaction mechanisms (Nucleophilic substitution in alkyl halides)
  8. 8. Stepwise (non-concerted) mechanisms Take place through reaction intermediates (species that can be detected or isolated) Radical Species with an unpaired electron Formed by the homolytic breakage of a chemical bond Ion Charged species Formed by the heterolytic breakage of a chemical bond
  9. 9. Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction(s) regardless of the size of the molecule it is a part of. However, its relative reactivity can be modified by nearby functional groups.
  10. 10. We say that the carbon atoms carrying functional groups that can be interconverted without the need for reducing agents (or oxidizing agents) have the same oxidation level
  11. 11. <ul><li>Types of organic chemical reactions </li></ul><ul><li>Substitution </li></ul><ul><li>Elimination </li></ul><ul><li>Addition </li></ul><ul><li>Oxidations </li></ul><ul><li>Reductions </li></ul>
  12. 12. Nucleophile: Neutral or charged reagent that forms a chemical bond to its reaction partner (the electrophile) by donating both bonding electrons. Anions Neutral species with a non-bonding electron pairs . Electrophile: Reagent that participates in a chemical reaction by accepting an electron pair (from the nucleophile) in order to form a chemical bond Cations Neutral species with polarized bonds . Nucleophilicity and electrophilicity are kinetic terms Substitution reaction at saturated carbons Nucleophilic substitution (SN) Some basic concepts
  13. 13. Properties of the C-X bond Alkyl halides are electrophiles
  14. 14. Concerted versus stepwise mechanism
  15. 15. S N 1 Reaction Stepwise mechanism/Planar intermediate/Racemization !! Reaction intermediate
  16. 16. S N 2 Reaction Concerted mechanism/Dorsal attack/Stereochemical control !!
  17. 19. Synthetic applications: alkenes
  18. 20. Stepwise elimination (E1) Carbocationic intermediate
  19. 21. Competition SN1/E1 are due to the fact that nucleophiles are also bases !! (dual character)
  20. 22. Stereochemical control !!
  21. 24. SN2 and E2 are also competing processes !!
  22. 25. All 4 processes (SN1, SN2, E1, E2) can compete !! However…… Not synthetically useful Synthetically useful !!