Orgo Ch 4.1-4.3

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Orgo Ch 4.1-4.3
2013-09-29 20:59:24
CHM 201

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  1. The most interesting and useful aspect of organic chem is __. 
    What can we do with reactions?
    • study of reactions
    • organize the reactions into logical groups based on how the reactions take place and what intermediates are involved
  2. __ of alkanes is a relatively simple substitution of a halogen for a hydrogen that can occur in the gas phase, without a __ to complicate the reaction.
    • halogenation
    • solvent
  3. In practice, alkanes are so __ that they are rarely used as starting materials for lab __. Their reactions are relatively __.
    • unreactive
    • organic syntheses
    • uncomplicated
  4. what is a mechanism
    step by step pathway from reactants to products
  5. thermodynaics
    the energetics of the reaction at equilibrium
  6. The amounts of __ and __ present at equilirbium depends on their relative __.
    • reactants and products
    • stabilities
  7. Even though the equilibrium may favor the formation of a __, the reaction may not take place at a __. To use a reaction in a realistic time period (and to keep the reaction from becoming __), we study its __, the variation of reaction rates with different conditions adn concentrations of __.
    • product
    • useful rate
    • violent
    • kinetics
    • reagents
  8. The __ is an important industrial reaction, with a relatively simple mechanism that illustrates many of the important principles of a reaction. The reaction of __ with __ produces a mixture of __ products, whose composition depends on the amount of __ added and also on the reaction conditions.
    • chlorination of methane
    • chlorine
    • methane
    • chlorinated
    • chlorine
  9. Either __ or __ is needed for the reaction to place at a useful rate. 
    What is the first reaction that takes place?
    • light or heat
    • methane+ chlorine--> chloromethane + hydrogen chloride
  10. The reaction may continue; __ or __ is needed for each step.
    • heat 
    • light
  11. What are the three aspects of the reaction?
    • mechanism
    • thermodynamics
    • kinetics
  12. mechanism
    complete, step-by-step description of exactly which bonds break, and which bonds form, adn in what order to give the observed products
  13. thermodynaics
    study of teh energy changes that accompany chemical and physical transformations. It allows us to compare the stability of reactants and products and predict which compounds are favored by the equilibrium
  14. Kinetics
    is the study of reaction ratees, determining which products are formed fastest. It also helps to predict how the rate will change if we change the reaction conditions
  15. Before we can propose a detailed mechanism for something, such as chlorination, what must we do?
    learn everything we can about how the reaction works and what factors affect the reaction rate and the product distribution
  16. A careful study of the chlorination of methane has established three important characteristics: 
    The chlorination does not occur at room temp in the absence of light. the reaction begins when light falls on the mixture or when it is heated. Thus, we know this reaction requires some form of energy to initiate it
  17. A careful study of the chlorination of methane has established three important characteristics: 
    The most effect wavelength of light is a blue color that is strongly absorbed by chlorine gas. This finding implies that light is absorbed by the chlorine molecule, activating chlorine so that it initiates the reaction with methane
  18. A careful study of the chlorination of methane has established three important characteristics: 
    The light-initated reaction has a high quantum yield. This means that many molecules of the product are formed for every photon of light absorbed. Our mechanism must explain how hundreds of individual reactions of methane with chlorine result from the absorption of a single photon by a single molecule of chlorine
  19. A __ has been proposed to explain the chlorination of methane. A __ consists of three kinds of steps:
    • chain reaction x2
    • 1) initiation step
    • 2) propagation steps
    • 3) termination steps
  20. Initiation step
    which generates a reactive intermediate
  21. Propagation step
    in which the reactive intermediate reacts with a stable molecule to form a product and another reactive intermediate, allowing the chain t continue until the supply of reactants is exhausted or teh reactive intermediate is destroyed
  22. Termination steps
    side reactions that destroy reactive intermediates and tend to slow or stop the reaction
  23. The first reaction of chlorination is a __: Chlorine does not add to methane, but a chlorine atom substitutes for one of the hydrogen atoms, which becomes part of the HCl by-product.
  24. The Initiation Step: Generation of __.
    __, absorbed by __ but not by __, promotes this reaction. Therefore, __ probably results from the absorption of light by a molecule of chlorine.
    • radicals
    • blue light
    • chlorine
    • methane
    • initation
  25. __ has about the right energy to __ a chlorine molecule (Cl2) into two chlorine atoms, which requires 242 kJ/mol.
    • blue light
    • split
  26. What do fishhook- shaped half arrows depic?
    represent the movement of single electirons
  27. What is a reactive intermediate?
    a short-lived species that is never present in high concentration because it reactions quickly as it is formed
  28. When a reactive intermediate has an unpaired electron, it is called the __l
    odd electron (radical electron)
  29. Species with unpaired electrons are called __ or __. They are __ because they lack an __.
    • radicals or free radicals
    • electron-deficient
    • octet
  30. The __ readily combines with an electron in another atom to __ and __.
    • odd electron
    • complete an octet
    • form a bond
  31. When a chlorine radical collides with a methane molecule, it __ a hydrogen atom from methane. One of the electrons in the C-H bond remains on carbon while the other combines with the __ on the __ to form the H-Cl bond.
    • abstracts (removes)
    • odd electron
    • chlorine atom
  32. The first step does what?
    forms only one of the final products. A later step must form the other final product
  33. Notice that the first propagation step begins with one __ and produces another __. The regeneration of a __ is characteristic of a __ of a chain reaction. The reaction can continue because another __ is produced.
    • free radical (the chlorine atom)
    • free radical (the methyl radical)
    • free radical
    • propagation step
    • reactive intermediate
  34. In the second propagation step, the __ reacts with a molecule of chlorine to form __. The __ of the methyl radical combines with one of the two electrons in the Cl-Cl bond to give the Cl-CH3 bond, and the chlorine atom is left with the __.
    • methyl radicalchloromethane
    • odd electron
    • odd electron
  35. In addition to forming chloromethane, the second propagation step produces another __, which can react with another molecule of methane, giving HCl and a __, which reacts with Cl2 to give __ adn regenerate yet another __.
    • chlorine radical
    • methyl radical
    • chloromethane
    • chlorine radical
  36. In this way, the chain reaction continues until what?
    the supply of the reactants is exhausted or some other reaction consumes the radical intermediates
  37. If anything happens to consume some of the __ without generating new ones, the chain reaction will __. Such a side reaction is called a __: a step that produces reactive intermediates (free radicals) than it consumes.
    • free-radical intermediates
    • slow or stop
    • termination reaction
  38. The combination of any two __ is a __ because it decreases the number of free radicals.
    • free radicals
    • termination step
  39. Other __ involve reactions of free radicals with the walls of thevessel or other contaminants. Although the first of these __ give chloromethane, one of the products, it consumes the free radicals that are necessary for teh reaction to continue, thus __, Its contribution to the amount of product obtained from the reaction is small compared with the contribution of the __.
    • termination steps x2
    • breaking the chain
    • propagation steps
  40. While a __ is in progress, the concentration of __ is very low. The probability that two __ will combine in a __ is lower than the probability that each will encounter a molecule of reactant and give a __.
    • chain reaction
    • radicals
    • radicals
    • termination step
    • propagation step
  41. The __ become important toward the end of the reaction, when there are relatively few molecules of reactants available. At this point, the __ are less likely to encounter a molecule of __ than they are to encounter __ (or the wall of the container). The chain reaction quickly stops.
    • termination steps
    • free radicals
    • reactant
    • each other