Final06-07ans - Some Answers to the 301X Final Examination,...

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Some Answers to the 301X Final Examination, January 24, 2007 1. The two diastereomers are, of course, the cis and trans diols. CH 3 OH OH CH 3 OH OH cis 1 trans 1 The simplest mechanism through which both diols would give 2 and 3 , is an S N 1-like process going through a common tertiary carbocation. H 3 O + CH 3 O H 2 3 CH 3 OH OH CH 3 OH OH cis 1 trans 1 H 3 O + H 2 O H 2 O CH 3 OH 2 OH CH 3 OH 2 OH CH 3 OH (a) CH 3 O H H 2 O (b) H H 2 O (a) (b)
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By contrast, the requirement for backside displacement in an intramolecular S N 2 reaction would lead to the formation of 2 from the trans isomer and 3 from the cis isomer. H 3 O + 2 3 CH 3 OH OH CH 3 OH OH cis 1 trans 1 H 3 O + H 2 O H 2 O CH 3 OH 2 OH CH 3 OH 2 OH displace from rear then deprotonate CH 3 OH OH 2 H = = OH 2 OH H CH 3 2. The first one is easy - protonate-deprotonate H 3 C O CH 3 H 3 C OH CH 2 H OH 2 H 3 C O CH 2 H H (+) OH 2 H 3 O +
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The second is a bit harder, but still not really taxing. There are two possible initial protonations, but only one can lead to the product shown. H 3 O + OH H 3 O + /H 2 O O OH OH H H or goes nowhere O H OH 2 The last one is another easy one - just protonate, then deprotonate: H 3 O + H 3 C O O 18 H H OH 2 + H 3 C O O H H 18 + (+) (+) H 2 O H 3 C O O H 18 note extensive resonance stabilization
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3. (a and b) H 3 C CH 3 H 3 C CH 3 H 3 C CH 3 H 3 C CH 3 N N N Ph 1 2 N N N Ph H 3 C CH 3 H 3 C CH 3 N Ph (c) In order to test whether the second step is one-step or two we need some sort of a stereochemical label (round up the usual suspects!). As only one of very many possibilities, cis -2-butene would do fine: CH 3 CH 3 H H N N N Ph CH 3 CH 3 H H N N N Ph CH 3 CH 3 H H N Ph CH 3 CH 3 H H N Ph CH 3 CH 3 H H N Ph + N 2 1 2 cis one- step able to rotate around C—C single bond 2 trans close close + N 2
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4. The first reasonable step is formation of either a bromonium ion or the corresponding
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This note was uploaded on 03/07/2010 for the course ORGO 1 AND V.0243 taught by Professor Jones during the Spring '10 term at NYU.

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Final06-07ans - Some Answers to the 301X Final Examination,...

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