Electrophilic Aromatic Substitution in Polysubstituted Benzenes

Anticipating the products of electrophilic aromatic substitution can be more difficult when two or more substituents compete for control. For example, both methyl and methoxy groups are ortho para directors, and compete for control in electrophilic substitution of 2-methylanisole. The reaction product depends on which substituent has the stronger directing influence. 

Display the electrostatic potential map for 2-methyl anisole. For which ring site, para to methyl or para to methoxy, is the electrostatic potential more negative Where do you expect electrophilic attack to occur Is your result consistent with the relative stabihties of intermediate benzenium ions formed upon addition of the electrophile Compare energies for 3-methyl-4-methoxybenzenium ion and 4-methyl-3-methoxybenzenium ion. 

6-Trinitrotoluene (TNT) is made by nitration of toluene. Display electrostatic potential maps for toluene, 4-nitrotoluene (the first nitration product) and 2,4-dinitrotoluene (the second nitration product). Are the second and third nitration steps likely to be easier or more difficult than the initial nitration of toluene Explain. 

Electrostatic potential map for 2-methylanisole shows negatively-charged regions (in red) as the likely sites of electrophilic attack. 

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