Practice Test 4

Practice Test 4 - Chem 10172, Spring 2008 (1) Br EXAM 4...

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Chem 10172, Spring 2008 EXAM 4 REVIEW PROBLEMS SOLUTIONS 1 (1) (a) Br K 2 CO 3 , H 2 O reflux 2.5 hr Br Br E1 (or E2) (b) H CH 3 Br 1) NaNH 2 2) C C CH 3 The first reaction deprotonates the acetylene to form the nucleophilic acetylide ion, which undergoes S N 2 with the benzyl bromide. (c) CH 3 OH Br Br 0 ºC CH 3 O Br + Br OCH 3 S N 1 conditions; 3º allyl bromide is much more reactive than the 1º bromide under these conditions. The resonance-stabilized allyl cation can react on either side. (d) OMe Br CH 3 NaI DMSO OMe I CH 3 OMe I CH 3 + 50:50, racemic S N 1 (3º, poor base so no E1) (e) OH SCH 3 1) TsCl, pyridine 2) NaSCH 3 , acetone Transformation will not work well in one step because acidic conditions needed to make the OH group leave are not compatible with the strongly basic nucleophile. (f) Cl NaO t Bu, BuOH, ! Bulky strong base and heat favors E2
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Chem 10172, Spring 2008 EXAM 4 REVIEW PROBLEMS SOLUTIONS 2 (2) (a) (8 pts.) Cumyl mesylate reacts in methanol to give mostly the methyl ether shown. Give a mechanism for this reaction. O S CH 3 O O CH 3 OH O CH 3 O S CH 3 O O O CH 3 CH 3 O H O CH 3 H CH 3 O H (CH 3 SO 3 might also act as the base) (b) (5 pts.) When the reaction is conducted in the presence of sodium methoxide, the major product has the spectra shown below. Indicate one feature of the spectrum that shows that the major product is not the methyl ether shown in (a). O S CH 3 O O CH 3 OH NaOCH 3 2 Some features include:
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Chem 10172, Spring 2008 EXAM 4 REVIEW PROBLEMS SOLUTIONS 3 Product has alkene hydrogens ( δ 5-5.5), methyl ether has none. Product has only one sp 3 carbon, methyl ether would have two. Product has only one CH 3 group in 1 H NMR (d 2.1 ppm, 3H), while methyl ether would have two (6H at ~1.5 ppm, 3H at ~3.5 ppm) (c) (10 pts.) Propose a structure for 2 and draw a mechanism for its formation. Reaction will be mostly E2 because of the presence of strong base: O S CH 3 O O CH 3 O H H CH 3 O + Cmpd. 2 (d) (6 pts.) If the rates of disappearance of cumyl mesylate under the conditions of (a) and (b) are compared, would (a) be faster; would (b) be faster; or would the two reactions go at the same rate? Justify your answer. In (a) the reaction is S
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This note was uploaded on 05/18/2008 for the course CHEM 10172 taught by Professor Brown during the Spring '08 term at Notre Dame.

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Practice Test 4 - Chem 10172, Spring 2008 (1) Br EXAM 4...

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