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Unformatted text preview: Zaza Atanelov July 6, 2010 Experiment #21: The Wittig Reaction I ntroduction: In this lab a Wittig Reaction is performed with 2-nitrobenzaldehyde and methyl(triphenylphosphoranylidene) acetate using silica gel (SiO 2 ). The Wittig Reaction facilitates the formation of a new carbon bond and is thus an important reaction that can be reproduced on a mass scale in todays society. At the conclusion of the experiment we want to assign the NMR spectra of the product and determine whether the trans or cis product of the reaction is more favored. In the experiment, microwave radiation is used to heat the reaction and the products are separated by column chromatography. A TLC can then be made to determine the purity of the fraction samples. I t is important to understand the differences between using TLC and column chromatography. The results show that the trans alkene isomer is the major product formed in the reaction, based on least steric hindrance. The results are general and serve to justify the fact that molecules tend to be oriented in a way that results in the least hindrance. Discussion: (/E/)-methyl-3-(2-nitrophenyl)acrylate is the major alkene isomer formed in the reaction along with the side product triphenylphosphine oxide. To decide the major alkene isomer (cis or trans), we first determine which would be formed based on the reaction mechanism. By analyzing the two possible products, we see steric strain on the cis conformation, as the ketone and benzene group invade each others space. This sets up the hypothesis that the trans formation is the major alkene space....
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