Midterm III KEY

Midterm III KEY - Version 1 (yellow) Problem 1. Rank the...

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Version 1 (yellow) Problem 1 . Rank the following six carbocations in increasing order of stability. (Least stable as #1).(7p) CH 3 Methyl carbocation Benzylic cation + 3°-cation 3°-cation Benzylic cation + 2°-cation 1°-cation 2°-cation 1 6 4 3 2 5 Problem 2 . Rank the following alkyl halides in order of decreasing S N 2 reaction rate using NaOCH 3 in methanol. Indicate the most reactive alkyl halide as #1. (8p) H 3 CB r Br Br Br Br Br 1 43 6 5 2 Methyl-bromide 1°-alkyl bromide 2°-alkyl bromide 2°-alkyl bromide (more sterically hindered than #4) 3°-alkyl bromide 1°-alkyl bromide (more sterically hindered than #2)
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Version 1 (yellow) Problem 3 . The reactions shown below are unlikely to occur as depicted. Indicate what is wrong and predict the true product. If no reaction will occur, explain. (8p) CH 3 OH CH 3 Br NaCl DMF H 3 C CH 3 CH 3 O K H 3 C H Cl Cl CH 3 CH 3 CH 3 OH CH 3 Cl CH 3 O CH 3 H 3 C H 3 C H CH 3 H 3 CO Cl CH 3 CH 3 A) (solvent) DMSO (Solvent) B) C) 1) Na H 2) CH 3 -I D) No rection! The chloride is unable to substitute OH, which is also a very poor leaving group Correct product(s): CH 3 Major CH 3 Minor SN2- product impossible with sterically hindered base used. PKa = 25 PKa = 50 Correct product: H 3 C CH 3 The most acidic protion will be removed and the C-anion will then undergo an SN2 with CH3I Cl OCH 3 CH 3 CH 3 Correct product: SN1-product using a 3°-alkyl chloride. The SN1 reaction always involve a
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This note was uploaded on 07/03/2008 for the course CHEM 231 taught by Professor Bergdahl during the Spring '08 term at San Diego State.

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Midterm III KEY - Version 1 (yellow) Problem 1. Rank the...

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