chem372w08hw4 - Chem 372 Winter 2008 Homework Assignment 4...

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Unformatted text preview: Chem 372 Winter 2008 Homework Assignment # 4 Due at class Thursday February 14th 1. The reaction of 1,3-butadiene and 1 mol of HBr yields a mixture of 1—bromo—2— butene and 3—bromo—l—butene. Why does it not form 4—bromo—1~butene? Explain clearly. 2. For each of the two dienes below write the structures for the various constitutional isomers resulting from the reaction with 1 mol. of HBr. In each reaction predict (if it is possible to do so) the product of kinetic and of thermodynamic control of the reaction. Note: For diene (b) this is a challenging question._ (6.2,) @ Q30 C0 3 In each of the following cases predict the product(s) formed. If mixtures are to be expected write all structures and, Where possible, indicate the major product. Pay careful attention to stereochemistry. \ CH3 H Bar (till high temperature CH3 Q’fl/ / /_EC_, 4. Each of the two molecules has been synthesized using a Diels Alder reaction. Carryout a retrosynthetic analysis and show the structures of the compounds used to make each of them. fl% ‘ MeOOC><fi O \ MeOOC N 5. Bicyclo— 2,5—heptadiene can be prepared in two steps as shown below. (a) Provide a mechanism for each step. Show all necessary “curly arrows” CLEARLY. (b) Write an equation to show how it could be made in one step using a familiar reaction. heat C H ONa + CH =CHC] —_) 2 s :> 2 / H ' C2H5OH [b C] Bicyclo-2,5-heptadiene 6. Classify each of the following structures as aromatic, antiaromatic or nonaromatic. Explain your decisions briefly. 7. All attempts to synthesise cyclopentadienone have yielded only a Diels Alder product While cycloheptatrienone is readily prepared and stable. (a) Why this difference? Provide an explanation. Hint : Consider resonance structures (b) Write the structure of the Diels Alder product from cyclopentadienone 0 2w —> aDiels-Alderadduct Cyclopentadienone Cycloheptatrienone ...
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