2007-203%20midterm2KEY

2007-203%20midterm2KEY - Chemistry 203 Midterm 2-Nov 13...

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Page 1 of 11 Chemistry 203 Midterm 2-Nov. 13, 2007 surname given names last initial student number signature MOLECULAR MODELS MAY BE USED 1 2 3 4 5 raw total total 23 10 11 24 12 80 10 1. (23 marks) Answer each of the following parts. a) Draw the major contributing resonance structures of anion A : C O N A C O N C O N b) Circle any compound that has only two signals in its 1 H NMR spectrum: O O O O all of these none of these c) Circle the alkyl bromide that would undergo reaction with sodium thiophenoxide (NaSPh) in a suitable solvent (under otherwise identical conditions) at the slowest rate. Br CH 3 Br Br Br Br H
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Student name/id number: ___________________________________________ Page 2 of 11 d) Consider the organic bromides 1 and 2 (below): Under otherwise identical conditions, the organic bromide that undergoes a S N 1 reaction at the slower rate is: 1 2 Br Br 1 2 (circle your answer) Justify your answer using brief comments (pictures=1000 words). 2° carbocation; positive charge localized in an empty p orbital alkenyl carbocation; positive charge localized in an empty sp 2 orbital -more s character; closer to nucleus; highly unfavorable to have positive charge there; this cation is too unstable to form readily (the activation energy to form this is too high) + e) Consider the following two reactions: Under otherwise identical conditions, the reaction that proceeds at the faster rate is: 1 2 N N ethyl bromide solvent ethyl bromide solvent S N 2 product S N 2 product (1) (2) (circle your answer) ii) Justify your answer using brief comments (pictures=1000 words).
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