Nucleophilic Substitution Chemistry
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Questions and Answers

What is a characteristic of a nucleophile?

  • Electron neutral and uncharged
  • Electron poor and positively charged
  • Electron rich and negatively charged (correct)
  • Electron poor and negatively charged

    • What occurs in a heterolytic cleavage reaction?

  • A carbocation and a hydride ion are formed
  • A carbocation and a free radical are formed
  • A carbanion and a free radical are formed
  • A carbanion and a hydride ion are formed (correct)

    • What is the term for the structure that is between the reactants and products in a nucleophilic substitution reaction?

  • Final product
  • Intermediate state
  • Transition state (correct)
  • Initial reactant

    • What is the result of oxidation in a redox reaction?

    <p>The compound loses electrons</p> Signup and view all the answers

    What is the term for the addition of oxygen to a molecule in a biological system?

    <p>Oxidation</p> Signup and view all the answers

    What is the term for the molecule that binds to the enzyme in a catalytic reaction?

    <p>Ligand</p> Signup and view all the answers

    What type of amino acids are present in the active site of the enzyme?

    <p>Both hydrophobic and polar amino acids</p> Signup and view all the answers

    What is the mechanism of acid-base catalysis?

    <p>Donation or gain of proton</p> Signup and view all the answers

    Which amino acid is responsible for facilitating acid-base catalysis?

    <p>Histidine</p> Signup and view all the answers

    What is the difference between specific and general acid-base catalysis?

    <p>Specific involves OH and H, while general involves other groups</p> Signup and view all the answers

    What is the net result of the covalent catalysis reaction?

    <p>A–X + B → A + B–X</p> Signup and view all the answers

    What is the role of the enzyme in covalent catalysis?

    <p>It forms a covalent bond with the substrate</p> Signup and view all the answers

    Study Notes

    Nucleophilic Substitution

    • A nucleophile is electron-rich, negatively charged, and seeks electrons.
    • An electrophile is electron-poor, positively charged, and seeks electrons.
    • High electronegativity leads to a more stable intermediate state, but not stable enough, as electrons are shared between carbon and oxygen.
    • To restabilize, electrons on oxygen move between oxygen and carbon, breaking one bond and re-establishing a double bond, and forming a leaving group.

    Cleavage Reactions

    • Heterolytic cleavage forms a carbanion and a hydride ion, carrying the shared electrons.
    • Homolytic cleavage breaks a bond, each compound taking one electron, forming highly reactive free radicals.

    Oxidation-Reduction Reactions

    • Oxidation involves electron transfer, resulting in the oxidized compound losing electrons.
    • Reduction involves electron gain, resulting in the reduced compound gaining electrons.
    • OIL RIG: Oxidation Is Loss, Reduction Is Gain.

    Biological Oxidation

    • Addition of oxygen, removal of electrons, or dehydrogenation (removing hydrogen, resulting in hydride ions).

    Chemical Catalysis

    • Enzyme: a protein that aids chemical reactions.
    • Substrate: the molecule on which the enzyme acts.
    • Active site: the enzyme's binding site, containing hydrophobic amino acids and polar amino acids facilitating acid-base or covalent catalysis.

    Types of Catalysis

    • Acid-base catalysis: donation or gain of protons, increasing the reaction rate through catalytic proton transfer.
    • Covalent catalysis: covalent bond formation between the substrate and enzyme.

    Acid-Base Catalysis

    • Histidine's imidazole group, with a pKa close to the solution's pH, donates/accepts protons, facilitating the reaction.
    • Base catalysis removes protons, indirectly participating in bond cleavage.
    • Acid catalysis involves proton donation.

    Covalent Catalysis

    • Substrate binds covalently to the enzyme (E), enabling covalent catalysis.
    • Example: Sucrose phosphorylase facilitates the reaction sucrose + Pi → glucose-1-P + fructose.

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    Description

    Learn about nucleophilic substitution reactions, including the roles of nucleophiles and electrophiles, intermediate states, and transition states.

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