Exam_2-Chem35-2007-answers

Exam_2-Chem35-2007-answers - Name_ SISD_ Chemistry 35 Exam...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Name____________________________ SISD________________________ 1 Chemistry 35 Exam 2 Answers - April 9, 2007 Problem 1 . (14 points) Provide the products for the reactions shown below. If stereochemistry is important, be sure to indicate stereochemistry clearly. If no reaction would occur, write NO REACTION. A) (2 points) No partial credit HO OH O PPh 3 , DEAD O O Intramolecular Mitsunobu reaction. B) (2 points) No partial credit MUST PROVIDE EXPLANATION!!! OMs Ph Ph Ph NaN 3 DMF NO REACTION This is similar to a neopentyl system. Beta branching does not allow an SN2 reaction to occur. C) (2 points) No partial credit Br SH N Li S The base is very strong, with a pKa around 35. However, it is a poor nucleophile because it is very sterically hindered due to the two tBu groups. This base deprotonates the thiol to generate a thiolate, which is a strong nucleophile. The thiolate initiates an intramolecular SN2 reaction with the benzyl bromide to give the cyclic thioether.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Name____________________________ SISD________________________ 2 D) (2 points) 2 points for either answer, but 2 points total. No partial credit. Ph OTs Ph OH O Ph O Ph Ph Ph O O O OR This is an SN1 reaction. The tosylate leaves to generate a carbocation. Resonance distributes the positive charge over two different carbon atoms, either of which can be attacked by acetic acid to generate the indicated products. E) (2 points) No partial credit. HO OH 1 equivalent of NaH 1 equivalent of MeI MeO OH NaH deprotonates the most acidic position, which is the phenolic OH rather than the benzylic OH. The resulting phenoxide ion does an SN2 reaction with MeI (Williamson ether synthesis) to generate the methyl ether product. F) (2 points) No partial credit. OK to show the Na salt of the product. S O O O NaN 3 CH 3 CN N 3 S OH O O The starting material is an internal sulfonic ester, and behaves just like a tosylate or mesylate. Azide is a strong nucleophile, and it attacks the sulfonic ester (SN2 reaction) to give the ring opened product. G) (2 points) No partial credit OH NH 2 PPh 3 , DEAD NO REACTION The Mitsunobu reaction only works with nucleophiles that have a conjugate acid with a pKa between 3 and 12. The primary amine in this reaction has a pKa of approximately 35, which is outside of this range.
Background image of page 2
Name____________________________ SISD________________________ 3 Problem 2 (14 points) A) (12 points) Provide a detailed, step-by-step mechanism for the following reaction. In this question, we provide the reactant and reaction conditions.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 11

Exam_2-Chem35-2007-answers - Name_ SISD_ Chemistry 35 Exam...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online