st Midterm Exam Version 1 Fall 2012 - ?· Chemistry 140C 1st Midterm Exam Version 1 Fall 2012 Mon, Oct…

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  • Chemistry 140C

    1st

    Midterm Exam Version 1

    Fall 2012

    Mon, Oct 22, 2012 11:05 am 11:45 am

    This exam accounts for 25% of the final grade.

    Mark your final answer clearly. Completely erase irrelevant information!

    Exams written in pencil will not be regraded.

    Additional pages are at the end for your convenience. You can use them to sketch

    formulae, mechanisms, etc. and for answers. Indicate if your final answer should be

    found on the additional pages at the end of the exam!

    Write your name and student ID on every page and sign every page.

    Good Luck! SOLUTIONS Your Name (Please print): ______________________________________ Your Student ID#: ______________________________________ Question 1: ../40

    Question 2: ../20

    Question 3: ../40

    Question 4: ../50

    Total points: ./150

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    140C - 1st Midterm exam, Version 1 10-22-2012 2

    Question 1: Heating of the ketone 1 with potassium hydroxide in water led to isolation of the bicyclic product 2.

    (a) Write a detailed mechanism that explains the conversion of 1 to 2. Show all intermediates! (20 points)

    (b) In addition to the product 2, unused starting material 1 was isolated from the reaction shown above. However, the re-isolated starting material 1 turned out to be a racemic mixture. Explain in one sentence and by using a structure!

    (20 points)

    The enolate is planar and can be protonated from either side:

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    140C - 1st Midterm exam, Version 1 10-22-2012 3

    Question 2: (a) Benzoyl chloride 3 is a much weaker base than benzamide 4. Explain, using resonance structures. (10 points)

    Resonance stabilization of the positive charge in the amide (not possible in the chloride). (b) Which of the benzoic acid derivatives, 3 or 4, would you use to prepare

    benzoyl acetate (5) according to the procedure shown below? Note your choice in the box and explain in one sentence. (10 points)

    Benzoyl chloride 3 is more reactive because of the electron withdrawing halide that increases

    polarization of the carbonyl group.

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    140C - 1st Midterm exam, Version 1 10-22-2012 4

    Question 3: Write a detailed mechanism that explains the acid-catalyzed hydrolysis of benzoyl acetate (5 in Question 2) to the carboxylic acid. Show all intermediates! Transfer protons via the solvent! (40 points)

    Ester hydrolysis following the addition-elimination mechanism.

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    140C - 1st Midterm exam, Version 1 10-22-2012 5

    Question 4: Heating of a mixture of benzaldehyde 6 and acetaldehyde 7 in aqueous sodium

    hydroxide furnishes the -unsaturated aldehyde 8. Write a detailed mechanism that explains the conversion. Show all intermediates! Transfer protons via the solvent!

    (50 points)

    Aldol condensation

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    140C - 1st Midterm exam, Version 1 10-22-2012 6