Midterm_2_practice_KEY

Midterm_2_practice_KEY - Chem140C Spring Finn Midterm 2...

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Chem140C – Spring – Finn Midterm 2 Practice Problems KEY Page 1 of 8 Chem 140C – Spring (Finn) Midterm Exam #2, Practice Problems Note: Most of these problems are too difficult for me to give on a test – you could do them, but it might take too much time. They are therefore excellent to help you prepare. 1. Draw the mechanism of each step in the two-step transformation: This is a Hoffman-type of elimination. N O Ph H (1) Ph Br (2) base N Ph Ph O (1) Ph Br N O Ph H Ph note: S N 2 reactions on benzlic halides are especially fast base
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Chem140C – Spring – Finn Midterm 2 Practice Problems KEY Page 2 of 8 2. Explain the trend in acidities of these protonated amines. N O H H N O H N H pK a = 0.8 pK a = 5.3 pK a = 11.0 A regular amide with N lone pair fully engaged with carbonyl group (strong resonance electron- withdrawing effect), so N is difficult to protonate (conjugate acid is a very strong acid) H N O N O N N lone pair on amide is orthogonal to carbonyl ! system, so doesn't overlap. But the basicity of N is somewhat diminished by the i n d u c t i v e electron-withdrawing effect of the carbonyl oxygen. A somewhat stronger amine base than usual (standard pK a of conjugate acid is about 10) because the substituents are "pulled back" slightly, making the lone pair more accessible. But by far the biggest effect with respect to the other compounds is the lack of carbonyl group.
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Chem140C – Spring – Finn Midterm 2 Practice Problems KEY Page 3 of 8 3. The reaction of a hydrazine with an acetylenic ester gives a pyrazolone. Write a detailed mechanism for the formation of the pyrazolone in the reaction below. [For
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This note was uploaded on 06/07/2008 for the course CHEM 140C taught by Professor Nefzi during the Spring '06 term at UCSD.

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Midterm_2_practice_KEY - Chem140C Spring Finn Midterm 2...

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