4.28 quiz key

4.28 quiz key - Weekly Quiz April 28, 2006 1. The leaving...

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Weekly Quiz April 28, 2006 1. The leaving group does play a role in the likelihood of the reaction. Which one of these two reactions is likely to proceed forward, and which one is not? Why? Draw reaction coordinate diagrams for these reactions. NH 2 NaOH DMSO OH O NaCl Cl HMPA S O O The second reaction is likely to happen. Tosylate is a great leaving group. In the first reaction the incoming nucleophile is a weaker nucleophile than the supposed LG. Therefore, if the NH2- is kicked off it will back attack. The reaction favors the reactant side. 2. Go back and consider the following reactions (you know these!) and suggest the mechanism it likely proceeds by. What evidence do you have to support this? a. Reaction of SOCl 2 with a secondary alcohol (shown below)
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OH S O Cl Cl HO S O Cl + NH 3 O S O Cl Cl - Cl + -OSCl O release SO 2 and Cl - This reaction is an SN2 reaction. It occurs preferentially at primary and secondary carbons, with a good LG and a good (charged Nu). Backside attack, and no carbocation intermediate. b. Reaction of a vicinal dibromide with strong base. E2 elimination. Strong base is used, and the E2 reaction is the strongest competitor f all substitution and elimination reactions. c. Reaction of an alkynl anion with a primary alkyl halide. SN2 reaction. The reaction conditions were a strong nucleophile (alkynal anion) and a primary alkyl halide. These conditions are ideal for an SN2 reaction. d.
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This homework help was uploaded on 04/20/2008 for the course CHEM 231 taught by Professor Montaguesmith during the Spring '06 term at Maryland.

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4.28 quiz key - Weekly Quiz April 28, 2006 1. The leaving...

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