We will discuss the results you obtained from the Wittig reaction you performed last week. You will also meet with your Synthesis Project Mentor sometime this week to go over your synthesis project.
Review the experiment you performed last week Exploring the Stereochemistry of the Wittig Reaction. Record the conditions you used for the experiment.
Read Section 18.7 ("Addition of Phosphorus Ylides: The Wittig Reaction") in your lecture text (Hornback, pp 758-765).
Write a mechanism for the Wittig reaction you ran last week.
Draw structures for the cis and trans products produced in the reaction.
Print out (and bring to lab) the alkene region of the H-NMR (5.5-6.5 ppm) from your Wittig reaction.
Analyze the alkene region of the H-NMR and determine which peaks correspond to the cis isomer and which to the trans isomer.
Assign the peaks in the GC to the cis and trans isomers and record the ratio of cis to trans for your experiment.
Due Friday, March 26, in your lecture section.
The report on your investigation of the stereochemistry of the Wittig reaction should follow the journal style outlined earlier: Title, Byline, Abstract, Introduction, Results, Discussion, Experimental Methods, and References. Reread the handout on writing a report before you start. Be sure to use the proper journal format in preparing figures, tables, etc.
You should include experimental details for your experiment only. But in the Results and Discussion section include the results from other students in the class as presented in the post-lab lecture.
The introduction should include a brief review of the Wittig reaction (with some comments about stereochemistry), followed by a brief introduction to the experiments you did.
In this report I recommend separating the Results and Discussion Sections. Your Results section should contain a table containing the E/Z ratios for the various experiments. This section should also include a discussion of how you know which peak on the GC corresponds with which isomer. Include a GC trace as a figure. Include a figure showing the vinyl proton region of the NMR, fully analyzed. Remember that a typical reader will not look at the Experimental section, so you need to provide enough information in the Results section so they have some idea about where the results come from. (Of course if they want to know exactly how it was done they will need to read the Experimental section.)
In the Discussion Section analyze your results in terms of the mechanism of the Wittig reaction. Explain why the cis product predominates under one set of conditions, but the trans under another.