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Chapter 9: Problem 187

Assuming the mechanism of 1,2 -cycloaddition is similar to cycloaddition (i.e., the Diels-Alder reaction), is the product obtained from the addition of cyclopentadiene and ketene the expected one? Explain.

Short Answer

Expert verified
In conclusion, assuming a 1,2-cycloaddition mechanism similar to the Diels-Alder reaction, the product obtained from the addition of cyclopentadiene and ketene would be a seven-membered ring compound. This product is not typical for a Diels-Alder reaction, as ketene is not an ideal dienophile, but the reaction is still feasible due to the electron-withdrawing group present in ketene.

Step by step solution

01

Understanding Diels-Alder Reaction

The Diels-Alder reaction is a [4+2] cycloaddition reaction where a conjugated diene reacts with a dienophile to form a cyclic product. The reaction has the following characteristics: - The diene must be in the s-cis conformation. - The dienophile should have electron-withdrawing groups to facilitate the reaction. - The reaction proceeds through a concerted mechanism, meaning that all bond formations and bond breaks occur simultaneously.
02

Analyzing the reactants

In this case, the two reactants are cyclopentadiene and ketene. Cyclopentadiene is a conjugated diene, and it can readily undergo a Diels-Alder reaction. Its structure is cyclic with a five-membered ring, and it has a diene system on one side. Ketene (CH2=C=O) can be considered a dienophile as it contains an electron-withdrawing carbonyl group (C=O), which makes the double bond between the carbon and oxygen more electrophilic.
03

Predicting the product of the 1,2-cycloaddition

In order to determine if the product obtained from the addition of cyclopentadiene and ketene is the expected one, we need to predict the product of the reaction using 1,2-cycloaddition mechanistics similar to the Diels-Alder reaction. The reaction between cyclopentadiene and ketene is not a typical Diels-Alder reaction, as ketene is an unsymmetrical dienophile with one double bond. However, assuming a mechanism similar to Diels-Alder, 1,2-cycloaddition between the diene (cyclopentadiene) and dienophile (ketene) would lead to the formation of a seven-membered ring compound.
04

Conclusion

In conclusion, considering the reactants involved and assuming a 1,2-cycloaddition mechanism similar to the Diels-Alder reaction, the product obtained from the addition of cyclopentadiene and ketene would be a seven-membered ring compound. This product is not typical for a Diels-Alder reaction, as ketene is not an ideal dienophile, but the reaction is still feasible given the electron-withdrawing group present in ketene.

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Most popular questions from this chapter

Formulate chain initiation, propagation, and termination steps for the polymerization of butadiene by a peroxide catalyst. Consider carefully possible structures for the growing-chain radical. Show the expected structure of the polymer.

What products would you expect from the Diels-Alder addition of tetracyanoethylene to cis, trans \(-2,4\) -hexadiene and cis, cis \(-2,4\) -hexadiene? Explain.

Sketch out the n.m.r. spectra, including spin-spin splitting (if any), expected for the following compounds: (a) \(\mathrm{BrCH}=\mathrm{C}=\mathrm{CH}_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{C} \equiv \mathrm{CH}\) (c) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}=\mathrm{C}=\mathrm{CHCH}_{2} \mathrm{OCH}_{3}\)

vic-Dibromides usually react with bases to produce more alkyne than conjugated diene. What factor(s) may be controlling this? Two exceptions to this "behavior are 1,2 -dibromo-cyclohexane and 2,3 -dichloro \(-2\), 3-dimethylbutane. How do you account for these exceptions?

Account for the fact that 2-methyl-1, 3-butadiene reacts (a) with HCl to yield only 3 -chloro-3 methyl-1-butene and 1 -chloro \(-3\) -methyl-2-butene; (b) with bromine to yield only 3,4 -dibromo-3-methyl-1-butene and 1, 4-dibromo-2-methyl-2-butene.
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