Pre-Lab Preparation Sheet - Moravian College Chemistry Department

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Pre-Lab Preparation Sheet - Moravian College Chemistry Department

CHEM 212-2011Ex3-1Experiment 3How Can a ComplexAlkene be Synthesized?RBr?R Mg Br?R'HO?Introduction:In our Monday discussions we have been working on understanding how syntheses of organiccompounds are devised. As you recall, the syntheses that we have devised involve two organicreactions:• Grignard reagent reaction with an aldehyde or ketone to form an alcohol,• Dehydration of the alcohol to form the final product alkene.The discussion of the retrosynthetic applications of dehydration on p. C6 of the lab manualillustrate how the two reaction above can be linked to synthesize a relatively complex alkenefrom simpler organic compounds. The our of class application on p. C6 requires that you devise2 different syntheses for two compounds “from simple monosubstituted aromatic compoundsand non-aromatic compounds with four of fewer carbon atoms.” These syntheses illustrate howsuccessive reactions can be linked together to produce an alkene with a particular carbon chainstructure. We will use one of your retrosynthetic pathways to devise and carry out a synthesis of2-methyl-3-heptene, the second molecule in the Out of Class Application. One question weconsidered in our retrosynthetic analysis of dehydration was the lack of specificity of doublebond positioning in the reaction. So we might expect to find that our final product will consist ofa mixture of alkenes with similar carbon chains. The final aspect of this experiment is thedetermination of the relative amounts of the various possible alkene products that are actuallyformed in the reaction.Part AA. How can we choose starting materials for the synthesis and get thesynthesis started?Pre-lab Preparation Assignment:1. Read this Pre-lab Preparation Assignment sheet.2. In Padías: Review: Extraction (pp. 116-125) & Drying Agents (pp. 125-126).3. In CGWW read:a. How to make a Grignard reagent (pp. 211-212)b. Secondary and tertiary alcohols: which organometallic, which aldehyde, which ketone?(pp. 220-222).4. Complete the Prelab activity on the course website by 10:00 PM on Sunday, March 13.5. Complete the Out of Class Application on p. C6 of the lab Manual.6. Devise you version of the apparatus described on the next page.7. In your lab notebook: (See Lab Manual pp. 14-16 for format.)a. Update the Table of Contentsb. Enter the title of this experiment and the Question of the Week.8. Bring your notebook and ideas on answers to the Question of the Week to the Monday LabDiscussion period.9. After the lab discussion, complete pre-lab assignment on the procedure handout to beprovided on Monday.


CHEM 212 Experiment 3 Ex3-2 Alkene SynthesisQuestion of the Week:How can we choose starting materials for the synthesis and get the synthesisstarted?In our retrosynthetic analyses activities we have used Grignard reagents to advantage in creatingcarbon structures. Our discussions have emphasized the need for absolute exclusion of waterfrom Grignard reaction mixtures until the carbon-carbon bond forming reaction is complete.This experiment will give you an opportunity to experience the techniques required tosuccessfully use a Grignard reagent in a multi-step synthesis of an organic compound. As wewill discover, getting the synthesis started requires some special precautions. Reading theassigned sections in Padías and CGWW should give you some sense of the important factors thatmight affect the reaction, but you will need to think specifically about how an apparatus can beconstructer to provide the appropriate environment for the reaction. You have had nearly twoyears of college chemistry laboratory experience. So, before coming to the Monday labdiscussion, draw on your experience as well as the information from your class experience andreading in CGWW and Padías to devise an apparatus that could accomplish:• Combining magnesium metal, dry ether and an alkyl halide in a dry atmosphere so that theycan react to form a Grignard reagent.• Successfully adding an aldehyde or ketone to the apparatus containing the newly synthesizedGrignard reagent without admitting any moisture.• Finally exposing the reaction mixture to an acidic aqueous solution to complete the formationof the alcohol product.Be prepared to draw and explain the workings of your apparatus when you arrive at the Mondaylab discussion.Key Terms/concepts/techniques:• Grignard Reaction.• Organic Synthesis• Retrosynthetic Analysis

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