Organic Chemistry (8th Edition)

Published by Pearson
ISBN 10: 0321768418
ISBN 13: 978-0-32176-841-4

Chapter 8 - Reactions of Alkenes - Problems: Problem 8-19

Answer

The mechanism for the addition of bromine water to cyclopentene will be the addition of halohydrins. The OH will be added instead of two halogens. The mechanism shows why trans product is formed and the formation of enantiomers.
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Work Step by Step

The mechanism for addition of halohydrins is the following: 1) Electrophilic attack forms a bromonium ion. 2) Back-side attack by water on the most substituted carbon opens the bromonium ion. 3) Water removes a proton to give the bromohydrin. The product would be trans because the water can attack only from bottom if the bromonium ion forms on the top, and vice versa. This makes bromine and OH on opposite sides. The enantiomers form in equal amounts because both the C in evolved in double bond, are equally substituted so equally likely to be attacked.
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