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Unformatted text preview: The Wittig Reaction Question: Does the stabilized Wittig reaction to form Ethyl Cinnamate lead primarily to the cis or trans product? Background: Formation of CC and C=C bonds is essential to organic synthesis. A number of means have been developed. Today you will carry out the Wittig reaction using a stabilized ylide and analyze the product by NMR. O O OEt H + O OEt Ph3P CH +
EtO O Your final product will be a mixture of the cis and trans alkenes. Using the NMR analysis, your goal will be to determine the product distribution and the identity of the major product. Procedure: Weigh 0.201 g of (carboxymethylene)triphenylphosphorane into a 3mL or 5mL conical vial and add 50 L of benzaldehyde. Stir/grind the mixture with a small spatula at room temperature for 15 minutes. At this point, the reaction should be done. Add 3 mL of hexanes and stir for a few more minutes. The solid triphenylphosphine oxide byproduct will crash out of solution. Remove the liquid with a filter pipet and place into a clean, tared container. Add a second 3 mL portion of hexanes and repeat the procedure. Evaporate the combined hexane portions. If solid is observed during the evaporation, repeat the filtering process. Obtain a mass of the product and prepare a sample for NMR using CDCl3. Comments: Fill out the attached handout and turn it in to your AI before leaving lab today! Name________________________________________________ Wittig Handout (25pts) Please attach spectra and a copy of your lab notebook to this handout. 1. (5pts) Propose a detailed mechanism for this reaction, including all arrows and mechanistic intermediates. 2. (3pts) What was the purpose of adding hexanes to this reaction? 3. (3pts) Is this reaction a high yielding or low yielding reaction? Give data and calculations to support your answer. 4. (7pts) Does the stabilized Wittig formation of Ethyl Cinnamate lead primarily to the cis or trans product? What data support this conclusion? Indicate important peaks on the NMR spectrum. 5. (7pts) What was the quantitative cis/trans product distribution of this reaction? Explain how you came to this number. Indicate important peaks on the NMR spectrum. ...
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- Summer '11