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Base-Catalyzed Alpha-Halogentation quiz

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  • What is the main difference between base-catalyzed and acid-catalyzed alpha-halogenation regarding the number of halogenations?
    Base-catalyzed alpha-halogenation can lead to polyhalogenation, while acid-catalyzed typically results in only one substitution.
  • What role does the base (such as OH-) play in base-catalyzed alpha-halogenation?
    The base deprotonates the alpha carbon to form an enolate, which then reacts with the halogen.
  • Why does polyhalogenation occur in base-catalyzed alpha-halogenation?
    Polyhalogenation occurs because each halogen added stabilizes the enolate, making further substitution of alpha hydrogens easier.
  • What is required for polyhalogenation to occur in base-catalyzed alpha-halogenation?
    Multiple alpha protons are required; if only one alpha proton is present, only one substitution occurs.
  • What is an enolate and how is it formed in this reaction?
    An enolate is a resonance-stabilized anion formed when a base removes an alpha proton from a carbonyl compound.
  • How does the presence of a halogen on the alpha carbon affect further halogenation?
    The halogen stabilizes the negative charge on the enolate, making it easier for additional alpha hydrogens to be substituted.
  • What happens when all alpha protons are replaced in base-catalyzed alpha-halogenation?
    The reaction stops because there are no more alpha protons available for substitution.
  • Why is the term 'may yield' used instead of 'will yield' for polyhalogenation?
    'May yield' is used because polyhalogenation only occurs if there are multiple alpha protons available.
  • What is the general outcome when a compound with only one alpha proton undergoes base-catalyzed alpha-halogenation?
    Only one halogenation occurs, as there is only one alpha proton to substitute.
  • What is the role of X2 in base-catalyzed alpha-halogenation?
    X2 acts as the halogen source that reacts with the enolate to substitute an alpha hydrogen with a halogen.
  • How does the reactivity of the alpha carbon change after the first halogenation?
    The alpha carbon becomes more reactive toward further halogenation due to stabilization by the first halogen.
  • What is the significance of the negative charge on the enolate in this mechanism?
    The negative charge allows the enolate to attack the halogen molecule, facilitating substitution.
  • What is an application of alpha-halogenation mentioned in the lesson?
    An application is the haloform reaction, which will be discussed in the next video.
  • What happens if you keep adding base and halogen to a compound with multiple alpha protons?
    The reaction continues until all alpha protons are replaced by halogens.
  • Why is base-catalyzed alpha-halogenation considered 'interesting' compared to other mechanisms?
    Because it can lead to complete substitution of all alpha hydrogens, resulting in polyhalogenation.