Orgo Ch 4.12-4.4.14

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DesLee26
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Orgo Ch 4.12-4.4.14
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2013-10-01 08:21:20
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CHM 201
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  1. In a __, every __ must occur quickly, or the __ will undergo unproductive collisions adn participate in __ steps.
    • free-radical chain reaction
    • propagation step
    • free radicals
    • termination
  2. __ reacts explosively with methane. A mixture of __ and methane must be heated to react, and __ does not react at all. __ reacts at a moderate rate.
    • fluorine
    • bromine
    • iodine 
    • chlorine
  3. __ is a substitution, where a halogen atom replaces the hydrogen.
    halogenation
  4. In the higher alkanes, does replacement matter? Why or why not?
    yes because it may lead to different products
  5. The __ shows that replacement of hydrogen atoms by chlorine is not ___. __ has six __ hydrogens (hydrogens bonded to primary Cs) and only two __ hydrogens (bonded to secondary c), yet the major product results from substitution of a __ hydrogen.
    • product ratio
    • random
    • propane
    • primary
    • secondary
    • secondary
  6. When a chlorine atom reacts with propane, abstraction of a hydrogen atom can give either a __ or a __. The structure of the __ formed in this step determines __.
    • primary or secondary radical
    • radical
    • the structure of the observed product
  7. Explain the energy for a methyl carbon in terms of the energy required to form a free radical.
    the energy is greatest for a methyl carbon adn it decreases for a primary carbon, a secondary C, and a tertiary C
  8. The more __, the less energy required to form the __.
    • highly substituted the carbon atom
    • free radical
  9. We say that __ is more selective than __ because the major reaction is favored by a larger amount.
    • bromination
    • chlorination
  10. As with __, the __ in__ is the first __ step: abstraction of a hydrogen atom by a bromine radical
    • chlorination
    • rate-limiting step 
    • bromination
    • propagation
  11. The energy differences between chlorination and bromination result from the __.
    differences in the bond-dissociation enthalpies
  12. The __ bond is weaker, and abstraction of a H atom by Br⋅ is __. This __ step explains why __ is much slower than __, but it still doesn't explain the enhanced selectivity observed with __.
    • HBr
    • endothermic x2
    • bromination
    • chlorination
    • bromination
  13. In bromination, the rate limiting first __ step is __, and the __ (correspnding to the activation energies) are closer to the __ than the __.
    • propagation
    • endothermic
    • energy maxima
    • products
    • reactants
  14. In chlorination, on the other hand, this frist step is __, and the __ are closer to the __, which are the same and have the same energy for either route.
    • exothermic
    • energy maxima
    • reactants
  15. TWo important differences are apparent in the reaction-energy diagrams for the first propagation steps of chlorination and bromination:
    first?
    the first propagation step is endothermic for bromination but exothermic for chlorination
  16. TWo important differences are apparent in the reaction-energy diagrams for the first propagation steps of chlorination and bromination:
    second?
    the transition states formthing the 1 degree and 2 degree radicals for the endothermic bromination have a larger energy difference than those for the exothermic chlorination even though the energy difference of the products is the same in both reactions
  17. Explain transition in terms of exo and endothermic
    In an endo reaction, the trans state is closer to the products in energy and its structure. In an exo reaction, the transition state is closer to the reactants in energy and in structure
  18. In the product-like transition state for bromination, the CH bond is nearly broken and teh carbon atom has a great deal of __. The enregy of this transition state reflects most of the energy difference of the __.
    • radical character
    • radical products
  19. In the reactant-like transition state for chlorination, the C-H bond is just beginning to break, adn the carbon atom has little __. This transition state reflects only a small part (about 1/3) of the energy difference of the __. Therefore, __ is less __.
    • radical products
    • chlorination
    • selective
  20. What is the Hammond Postulate
    related species that are closer in energy are also closer in structure. The structure of a transition state resembles the structure of the closest stable species
  21. The transition state is always the point of __ on the energy diagram. Its structure resembles either the reactants or the products, whichever ones are __.
    • highest energy
    • higher in energy
  22. In an endothermic reaction, the __ are higher in energy, and the transition state is __.
    • products
    • product-like
  23. In an exothermic reaction, the __ are higher in energy, adn the transition state is __.
    • reactants
    • reactant-like

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