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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
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
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
2w —> aDiels-Alderadduct Cyclopentadienone Cycloheptatrienone ...
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- Spring '08