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3.22: Quiz 4A Key

  • Page ID
    19276
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    1. (9 pts) Drawing curved arrows to represent electron motion in a reaction mechanism. Use curved arrows to show the reaction mechanism and provide products for each of the following reactions. Don’t forget to show lone pairs and formal charges!

    1.png

    1. (5 pts) For the following pair of compounds, circle which compound has a more nucleophilic nitrogen and explain your answer.

    2.png

    A more nucleophilic nitrogen will have the electrons more available to attack an electrophile (more electron density more available makes a better Nuc). Compound B has localized electrons (and a negative charge). But compound A has delocalized electrons into the adjacent C=O pi bond, which means that the negative charge is spread out and not as available to attack an electrophile. Therefore, B is more nucleophilic because the electrons are not delocalized.

    1. (8 pts) For the following pairs of compounds, circle the compound that is a stronger acid then explain your answer. Your answer should include a drawing of the conjugate base for each acid.

    3a.png

    Conjugate base of carboxylic acid is more stable because the anion has resonance with π-bond (delocalized electrons). Both have electronegative Br for the inductive effect.

    3b.png

    Both anions are on an oxygen atom and there is no resonance. So, we must consider the inductive effect from the electronegative halide anions. F is more EN, so it has a greater inductive effect to stabilize the conj. base.

    Must show negative charge on conj. base!

    1. (6 pts) Rank the following compounds based on their boiling point (where 1 = highest boiling point) and provide an explanation for your answer. As part of your answer, please indicate the major intermolecular force that determines the boiling point of each molecule. (Note: the numerical ranking answers will not receive credit without the correct explanation.)
    4a.png 4b.png 4c.png
    1 3 2

    The more forces between the molecules, the more energy needed to boil/break apart.

    Compound A has van der Waals, dipole-dipole and most importantly, hydrogen-bonding interactions.

    Compound B only has van der Waals, which are the weakest forces.

    Compound C has all the same as compound A, but the dipole and hydrogen-bonding forces are weaker because nitrogen is less electronegative than oxygen.

    1. (8 pts) Draw a contributing resonance structure for each of the following compounds that demonstrates how the electrons are delocalized in each molecule. You must show curved arrows and include all formal charges.

    5a.png

    No charges.

    5b.png

    2 charges

    must have a negative charge on oxygen and a positive charge on nitrogen

    1. (6 pts) I am starting to look for questions to use on the final exam and you have a chance to help! Write your own “explain” question and then provide the correct answer. Your question/answer must be based on the lecture material covered so far, and of course it must be accurate and fair. (I will select at least one of these student questions to put on the final exam...)

      Must be an "explain" question. (Cannot be hybridization labeling or multiple choice, etc.)

    3.22: Quiz 4A Key is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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