Question

Both the E and Z diastereomers of 2-pentene can react with bromine to from 2,3-dibromopentane. (E) Br2 arty 4 stereoisomers a. Draw the 4 possible stereoisomers of 2,3-dibromopentane. b. Using a mechanism, prove that E-2-pentene can only form the 2S, 3R and 2R, 3S stereoisomers. c. Using a mechanism, prove that Z-2-pentene can only form the 2S,3S and 2R, 3R stereoisomers.

Answer 1

can react with Q. Both the E and Z diasteomers of a-pentene bromine to form 2,3 dibromo pentance. Br 1. a. Draw the -4- possible stereoisomers of 2,3-dibromo pentame AMS & The possible structure are // BY 1. b Using a mechanism prove that E-2-pentene can only Form the 25, 38 and 28,35 stereoisomers Aws:- DiBromination of alkene take place via bromonium cation intermediate which give Traus dibromination with bro like SN2 type

* Mechanism (brominium cation ) OS Br Br 2S, 3R 2R, 35 After formation of Bromomum ion upcoming nucleophile Bo can attack from the backside of eigther o carbon or Cz Carbon. Then the products are as, BR and 2R, 35 respectively. c. Using mechanism, prone that z-2-pentene form the 25,35 and 2R, BR stereoisomers can only DS Br 25,35 Br Br 2R, BR

Similarly Z-2-pentene form bromonium eation and gine trans bromination and form 2R, 3R dibromopentane and as, as dibromopentane. if we rolate ca Carbon then we get the zig-zag geometry G holation Bor Br Rx then b-bromine goes toup Erolation Bo then - bromine goes to down * If you do not undestand orientation do it by model then you can understand easily.