Chapter 15: Q 18P (page 778)
Predict the products of the following Diels-Alder reactions.
a)
b)
c)
d)
Short Answer
a)
b)
c)
d)
Chapter 15: Q 18P (page 778)
Predict the products of the following Diels-Alder reactions.
a)
b)
c)
d)
a)
b)
c)
d)
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Get started for freeQuestion: When N-bromosuccinimide is added to hex-1-ene in and a sunlamp is shone on the mixture, three products result.
(a)Show that the [4+4] cycloaddition of two butadiene molecules to give cycloocta-1,5-diene is thermally forbidden but photochemically allowed.
(b)There is a different, thermally allowed cycloaddition of two butadiene molecules. Show this reaction, and explain why it is thermally allowed. (Hint: Consider the dimerization of cyclopentadiene.)
In Solved Problem 15-2, we simply predicted that the products would have a 1, 2-or 1, 4-relationship of the proper substitutents. Draw the charge-separated resonance forms of the reactants to support these predictions.
Question: When Br2 is added to buta-1,3- diene at -150C , the product mixture contains 60% of product A and 40% of product B. When the same reaction takes place at 600C , the product ratio is 10% A and 90% B.
a. Propose structures for products A and B (Hint: In many case, an allylic carbocation is more stable than a bromonium ion.)
b. Propose a mechanism to account for formation of both A and B.
c. Show why A predominates at -150C and B predominates at 600C .
d. If you had a solution of pure A, and its temperature were raised to600C , what would you expect to happen ? Propose a mechanism to support your prediction.
When methylenecyclohexane is treated with a low concentration of bromine under irradiation by a sunlamp, two substitution products are formed.
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