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Exam Answers - CHEM 302 Organic Chemistry Exam II November...

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CHEM 302 Organic Chemistry Exam II November 2006 Answers 1) Provide mechanisms or reasonable syntheses, as appropriate for the following. (As in all syntheses or mechanism problems, you should think STEPWISE: what must happen first? What can then happen? And so on. Just take it easy, and think everything through.) a) Br(CH 2 ) 5 Br + NaOH O Clearly a mechanism question. How to convert 1,5-dibromopentane into oxacyclohexane (a.k.a. tetrahydropyran) Here is my thinking on it: Br Br - OH O Br H ! Br O H - OH O b) S S from 1,3-dibromopropane. ( Hint : think about what good nucleophile you might need, and how you might generate it.) This appears to be a synthesis problem. Here is one approach:
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Br Br NaSH NaSH HS SH Br(CH 2 ) 3 Br HS S Br ! S HS Br S S Arguably, one could start with the propane-1,3-dithiol and the 1,3- dibromoproprane and make the same compound. c) The synthesis of 2,2-dimethyl-3-octyne using reagents containing no more than six carbon atoms. Clearly another synthesis problem, but this time, with different restrictions. Maybe drawing the desired product will help. Here is a sensible disconnect If we disconnect as shown, we have a six-carbon fragment on the left, and a four carbon fragment on the right. Seems to be within our restrictions. Here’s the plan:
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H 1) NaH/THF 2) CH 3 (CH 2 ) 2 CH 2 Br d) (CH 3 ) 3 COH + HBr (conc) (CH 3 ) 3 CBr Another mechanism problem. Judging by the tertiary alcohol, I would guess an S N 1 reaction. Here’s the arrow formalism: OH H Br OH 2 Br - Br 2) In each of the following reactions, one essential part is represented as “X.” In
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This note was uploaded on 04/09/2010 for the course CHEM 302 taught by Professor Myers during the Fall '09 term at Simons Rock.

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Exam Answers - CHEM 302 Organic Chemistry Exam II November...

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