Question

Two stereoisomers are obtained from the reaction of HBr with (3S,4S)-4-bromo-3-methyl-1-pentene.1 Propose a mechanism for the reaction(provide a three-dimentional representation of the intermediates).Draw the structure of the two stereoisomers that form,showing stereochemistry of the new chiral centre.2. one of the stereoisomers is optically inactive.circle the optically inactive compound and explain why it is optically inactive.

Answer 1

1. The mechanism for the formation of two stereoisomers by the reaction of HBr with (3S,4S)-4-bromo-3-methyl-1-pentene can be drawn as follows.

2. Out of the two obtained stereoisomers, (2S,3R)-2,3-dibromo-3-methylpentane, which is circled in the scheme shown above, is an optically inactive meso isomer.

Reason: This meso isomer is optically inactive due to the internal compensation of the rotations of both the stereocenters present in it.