When Br2 is added to buta-1,3-diene at -15 °C, the product mixture contains 60% ofproduct A and 40% of product B. When the same reaction takes place at 60 °C, theproduct ratio is 10% A and 90% B.(a) Propose structures for products A and B. (Hint: In many cases, an allylic carbocationis more stable than a bromonium ion.)

When Br2 is added to buta-1,3-diene at -15 °C, the product mixture contains 60% ofproduct A and 40% of product B. When the same reaction takes place at 60 °C, theproduct ratio is 10% A and 90% B.(a) Propose structures for products A and B. (Hint: In many cases, an allylic carbocationis more stable than a bromonium ion.)

Organic Chemistry

8th Edition

ISBN:9781305580350

Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote

Publisher:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote

Chapter20: Dienes, Conjugated Systems, And Pericyclic Reactions

Section20.6: Sigmatropic Shifts

Problem 20.12P

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When Br2 is added to buta-1,3-diene at -15 °C, the product mixture contains 60% ofproduct A and 40% of product B. When the same reaction takes place at 60 °C, theproduct ratio is 10% A and 90% B.Show why A predominates at -15 °C and B predominates at 60 °C.
When Br2 is added to buta-1,3-diene at -15 °C, the product mixture contains 60% ofproduct A and 40% of product B. When the same reaction takes place at 60 °C, theproduct ratio is 10% A and 90% B.(a) Propose structures for products A and B. (Hint: In many cases, an allylic carbocationis 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 -15 °C and B predominates at 60 °C.(d) If you had a solution of pure A, and its temperature were raised to 60 °C, what wouldyou expect to happen? Propose a mechanism to support your prediction
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