PS_4_Answer_Key_2011

PS_4_Answer_Key_2011 - Massachusetts Institute of...

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This material may not be reproduced or posted on an internet website without written permission of Professors Danheiser and Jamison. Massachusetts Institute of Technology Organic Chemistry 5.12 March 15, 2011 Hyung Kyoo Kwon, Yu-Pu Wang & Phil Hamzik Problem Set #4 Solutions 1. Predict the product(s) of the following reactions and account for the regiochemical and stereochemical course of each transformation. Be sure to include all the stereoisomeric forms of each product that can be formed in the reaction. If multiple products are expected, indicate the isomeric relationship between each compound (constitutional isomers, diastereomers, or enantiomers). ANSWER: a) Ph PhCO 3 H H H Ph O O O Ph H Recall that epoxidation occurs with syn addition of oxygen to the alkene; in this case, the products resulting from attack on either face of the alkene are enantiomers. Ph O Ph b) Ph Ph O Ph O * * * In this case, the presence of the stereogenic center marked with * makes the two products diastereomers. PhCO 3 H
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This material may not be reproduced or posted on an internet website without written permission of Professors Danheiser and Jamison. c) Ph cat. OsO 4 NMO aq acetone * Ph Ph * * OH OH OH OH Osmylation gives syn addition of two hydroxyl groups to an alkene; just like in (b), the presence of the stereogenic center marked with * makes the two products diastereomers. d) Ph 1 equiv Br 2 CH 2 Cl 2 Ph H Br Br Bromination of an alkyne adds one equivalent of Br 2 across the triple bond with trans geometry. Had two equivalents of Br 2 been u sed , the p rodu c t wou ld be tetrabrominated species shown below: Ph Br Br H Br Br e) Ph Ph H Br Br 1 equiv Br 2 CH 2 Cl 2 Again, only one product results for the reason mentioned in the answer to (d). The presence of a stereogenic center in the starting material in this case has no effect on the nature of the product distribution, since only one product is produced. Again, if two equivalents of Br 2 had been used, we would have formed the product shown below: Ph Br Br H Br Br
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This material may not be reproduced or posted on an internet website without written permission of Professors Danheiser and Jamison. 2. An achiral compound, "X", has the molecular formula C 11 H 18 . Hydrogenation of X furnishes two products separable by careful distillation, each with the formula C 11 H 22 . One of these compounds is optically active, and the other is not. Ozono lys is of X produces acetone and an unidentified second compound. Based on this experimental data, what are three possible structures for X? Would knowing the identity of the other ozonolysis product allow you to unambiguously identify compound X? X O 3 , CH 2 Cl 2 then Me 2 S O + unidentified second product ANSWER: First, calculate the degrees of unsaturation from the molecular formula.
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This note was uploaded on 02/14/2012 for the course CHEMISTRY 5.12 taught by Professor Saraho'connor during the Fall '09 term at MIT.

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PS_4_Answer_Key_2011 - Massachusetts Institute of...

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