7.5 Nomenclature

• Many benzene derivatives are called by their common historical names.

  

• Disubstituted benzenes can also called by historical names. They are named using the prefixes ortho-, meta-, and para- to specify the position of the substituents.

  

• The seven carbon unit consisting of a benzene ring and a methylene (-CH₂-) group is named as a benzyl group and the seven carbon unit consisting of a benzene ring and a carbonyl (C=O) group is named as a benzoyl group.

  

• Numbers can also be used to specify the position of the substitution in disubstituted benzenes.

  

7.6 Electrophilic Substitution Reactions

The π-bond electrons in benzenes attack a strong electrophile and lose its aromaticity to give a resonance stabilized carbocation, called a sigma complex. Loss of the proton on the tetrahedral carbon atom of the sigma complex helps to regain the aromaticity. The overall reaction is the electrophilic aromatic substitution reaction (Scheme 3).

Scheme 3