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Ht2-04an - Answers to Hour Examination#2 Chemistry 301-301A...

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Answers to Hour Examination #2, Chemistry 301-301A - 2004. 1a. In general, sodium hydride forms the alkoxide which then does an intramolecular S N 2 to form the epoxide. OH OTs NaH O OTs O 3 The stereochemical details are critical, however, as the energy minimum chair form cannot undergo the critical S N 2 reaction, and must flip into the less stable diaxial form first so that the critical rear-side displacement can occur: O O OTs O OTs 3 (b) In the cis compound there is no arrangement in which there can be a proper S N 2 displacement (displacement from the rear). O OTs O OTs (c) The trans-fused second ring makes the necessary ring flip impossible, and thus the proper arrangement for displacement from the rear cannot be achieved. O OTs H H no ring flip possible 5 (alkoxide of 5 , really)
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2. The problem shows cyclohexanes, so immediately we know we have to draw good chairs, and that the tert -butyl group is equatorial: (CH 3 ) 3 C Cl (CH 3 ) 3 C Cl H H (CH 3 ) 3 C Cl (CH 3 ) 3 C Cl 7 = 8
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Ht2-04an - Answers to Hour Examination#2 Chemistry 301-301A...

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