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Nucleophiles and Basicity quiz #1

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  • How does the nucleophilicity of halide ions (F⁻, Cl⁻, Br⁻, I⁻) rank in water, and what is the reason for this trend?
    In water, which is a protic solvent, the nucleophilicity of halide ions increases as you go down the group: I⁻ > Br⁻ > Cl⁻ > F⁻. This is because smaller ions like F⁻ are more tightly solvated by water molecules, making them less available to donate electrons, while larger ions like I⁻ are less solvated and thus better nucleophiles.
  • What is the Lewis definition of a nucleophile?
    A nucleophile is defined by the Lewis definition as a good electron donor. This means it readily donates electrons to other species.
  • How does the Bronsted-Lowry definition describe a base?
    A base is described by the Bronsted-Lowry definition as a good proton acceptor. It readily accepts protons from other molecules.
  • Why do bulky nucleophiles tend to be less nucleophilic but more basic?
    Bulky nucleophiles have difficulty approaching electrophiles to donate electrons, making them less nucleophilic. However, their size allows easier access to protons, increasing their basicity.
  • How does nucleophilicity generally change with electronegativity?
    Nucleophilicity increases as electronegativity decreases. Less electronegative atoms are better at donating electrons.
  • What effect does moving up the periodic table have on nucleophilicity and basicity?
    Moving up the periodic table generally increases both nucleophilicity and basicity. This is due to smaller atomic size and weaker electron retention.
  • What is the role of protic solvents in affecting nucleophilicity?
    Protic solvents can hydrogen bond and solvate negative ions, covering them with solvent molecules. This solvation makes smaller ions less available for electron donation.
  • Why is iodide a better nucleophile than fluoride in protic solvents?
    Iodide is larger and more loosely solvated, making it more available to donate electrons. Fluoride is tightly solvated and less able to act as a nucleophile.
  • How does the trend of nucleophilicity for halide ions differ in aprotic solvents compared to protic solvents?
    In aprotic solvents, the trend is that fluoride is the best nucleophile and iodide is the worst. This is the opposite of the trend in protic solvents.
  • Why is it important to memorize nucleophilicity trends for different solvents?
    Memorizing these trends is crucial for answering conceptual exam questions about nucleophiles. It helps predict reaction outcomes and understand organic mechanisms.