Chapter 16.SE, Problem 72AP

Interpretation Introduction

Interpretation:

By drawing the resonance structures of the carbocation intermediates, among the two alkenes shown, which will react faster with HBr is to be predicted and explained.

Concept introduction:

The mechanism of addition of HBr to alkenes involves the formation of a more stable carbocation which is attacked by the Br- ion in the second step. Electron releasing groups in the aromatic ring can stabilize the carbocation through resonance while the electron withdrawing substituents will destabilize it. Hence those compounds with an electron releasing substituent on them will react faster than those with electro withdrawing substituent.

To predict:

Knowing the mechanism of HBr addition to alkenes and having an idea about the effects of various substituent groups on aromatic substitution, which of the two alkenes shown will react faster with HBr.

To explain:

The answer given by drawing the resonance structures of the carbocation intermediates.