Chapter 18.11, Problem 23ATS

Interpretation Introduction

Interpretation:

Synthesis of ortho-bromophenol has to be given starting from phenol.

Concept Introduction:

• Electrophilic substitution reaction is a type of reaction in which a particular group or atom in a compound is replaced by electrophile. An electrophile is a species that is deficient of electrons
• Benzene is an electron rich aromatic compound and undergoes electrophilic substitution reactions.
• The position that the electrophile occupies in the ring system depends on various factors like – presence of substituents, activation and deactivation of the ring etc.
• The pi electrons of the aromatic system must be available freely for the reaction to occur. Further, the aromatic ring must not have many bulk substituents on it to ease the any type of electrophilic substitution reaction. Presence of many bulk substituents hinders the ability of the delocalizing pi electrons to bond with the electrophile.

Deactivators are electron withdrawing groups attached to the benzenes that have either positive charge or an atom with high electronegativity. They are meta directors.

Activators are electron donating groups attached to the benzenes that have either electron density that is able to push into benzene ring or a lone pair of electrons. They are ortho–para directing.

Reaction between $conc.H_{2}S{O}_4$ and phenol is called sulfonation of phenol. Here, hydrogen atom of phenol is replaced by $-HS{O}_4$ group.

Bromination: In halogenation reaction, hydrogen atom of a molecule is replaced by a bromine atom.