Chapter 12, Problem 12.34P

Interpretation Introduction

Interpretation:

${\text{Br}}_{\text{2}}$ undergoes electrophilic addition to maleic anhydride as shown in the given reaction. The reason for this reaction being slower than the analogous one with $\text{cyclopentene}$ is to be explained.

Concept introduction:

Molecular bromine undergoes anti addition across a $\text{C=C}$ double bond. As the electron-rich alkene approaches ${\text{Br}}_{\text{2}}$ molecule, it temporarily generates an electron-poor site on the Br atom closer to the alkene. The subsequent flow of electrons takes place between the electron-rich alkene and the electron-poor Br atom. The presence of an electron withdrawing group near to the $\text{C=C}$ double bond makes it less electron rich which can diminish the driving force for the electrophilic addition step.