Chapter 23, Problem 23.3P

Interpretation Introduction

Interpretation:

A diagram similar to Figure $\text{23-1 }$ that illustrates the formation of the para and meta intermediates during the nitration of phenol is to be drawn and which of those two arenium ions is more stable is to be explained.

Concept introduction:

When nitration occurs at the ortho position, the arenium ion that is produced has four total resonance structures, allowing the positive charge to be delocalized over four separate atoms. By contrast, when nitration occurs at the meta position, the arenium ion intermediate has just three total resonance structures. The ortho arenium ion intermediate, with its additional resonance structure, is, therefore, lower in energy (more stable) than the meta intermediate. The additional resonance structure for the ortho intermediate is due to the involvement of the lone pair of electrons from the OH group. The involvement of that lone pair is not possible for the meta intermediate because the meta intermediate has no resonance structure in which C1 is directly attached to OH.