lecture 6 - Alkenes Reactions The most characteristic...

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1 Reactions Reactions of Alkenes of Alkenes ± Chapter 6 Chapter 6 Alkenes Reactions Alkenes Reactions ± The most characteristic reaction of alkenes is addition to the carbon-carbon double bond The pi bond is broken and, in its place, sigma bonds form to two new atoms or group of atoms. Characteristic Reactions (overview) (overview) C C CC Br 2 (HX) HCl H 2 O (X 2 ) B r 2 2 ) H 2 O (X) H OH Br (X) HO Br (X) H Cl (X) Descriptive Name(s ) Reaction + + + Bromination (halogenation) Hydrochlorination (hydrohalogenation) Hydration + Bromo(halo)hydrin formation Characteristic Reactions Characteristic Reactions C C C C BH 3 OsO 4 H 2 Hg(OAc) 2 H 2 O 2 H C C OH H H HgOAc + + + Hydroboration Diol formation (oxidation) Hydrogenation (reduction) + Oxymercuration Reaction Mechanisms ± A reaction mechanism describes how a reaction occurs which bonds are broken and which new ones are formed the order and relative rates of the various bond-breaking and bond-forming steps Reaction Mechanisms Reaction Mechanisms ± A reaction mechanism describes how a reaction occurs if in solution, the role of the solvent if there is a catalyst, the role of a catalyst the position of all atoms and energy of the entire system during the reaction
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2 Energy Diagrams Energy Diagrams ± Energy diagram: Energy diagram: a graph showing the changes in energy that occur during a chemical reaction ± Reaction coordinate: Reaction coordinate: a measure in the change in positions of atoms during a reaction Reaction coordinate Energy Energy Diagrams Energy Diagrams ± Enthalpy change, Enthalpy change, ΔΗ ΔΗ 0 : : the difference in total bond energy between reactants and products a measure of bond making (exothermic) and bond breaking (endothermic) Energy Diagrams ± Heat of reaction, Heat of reaction, ΔΗ 0 : the difference in enthalpy between reactants and products exothermic reaction: exothermic reaction: a reaction in which the enthalpy of the products is lower than that of the reactants; a reaction in which heat is released (ΔΗ 0 = = −) endothermic reaction endothermic reaction: a reaction in which the enthalpy of the products is higher than that of the reactants; a reaction in which heat is absorbed (ΔΗ 0 = +) = +) Activation Energy Activation Energy (from kinetics) (from kinetics) ± Transition state: an unstable species of maximum energy formed during the course of a reaction a maximum on an energy diagram Activation Energy (from kinetics) ± Activation Energy, Ea or Activation Energy, Ea or Δ G : the difference in Gibbs free energy between reactants and a transition state if Δ G is large, few collisions occur with sufficient energy to reach the transition state; reaction is slow if Δ G is small, many collisions occur with sufficient energy to reach the transition state; reaction is fast Energy Diagram a one-step reaction with no intermediate (bond breaking of reactants and bond formation of products occur simultaneously)
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3 Reactive Reactive Intermadiate This is a high-energy species, formed between
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This note was uploaded on 09/06/2009 for the course CHEM chem 12 AB taught by Professor Valentin during the Spring '09 term at Evergreen Valley.

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lecture 6 - Alkenes Reactions The most characteristic...

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