Substituent Effects in Substituted Aromatic Rings

Only one product can form when an electrophilic suhstitution occurs on benzene, hut what would happen if we were to carry out a reaction on an aromatic ring that already has a substituent A substituent aheady present on the ring has two effects. 

Substituents affect the orientation of the reaction. The three possible disubstituted products—ortho, meta, and para—are usually not formed 

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Predicting the Product of an Electrophilic Aromatic Substitution Reaction 

Rank the compounds in each of the following groups in order of their reactivity to electrophilic substitution  

R Substituents affect the reactivity of the aromatic ring. Some substituents activate the ring, making it more reactive than benzene, and some deactivate the ring, making it less reactive than benzene. In aromatic nitration, for instance, an -OH substituent makes the ring 1000 times more reactive than benzene, while an —N02 substituent makes the ring more than 10 million times less reactive. 

0 Substituents affect the orientation of the reaction. The three possible disub-stituted products—ortho, meta, and para—are usually not formed in equal amounts. Instead, the nature of the substituent already present on the benzene ring determines the position of the second substitution. Table 16.1 lists 

Interactive to use a web-based palette to predict products from electrophilic aromatic substitutions on substituted arenes. 

One further point inductive effects and resonance effects don t necessarily act in the same direction. Halogen, hydroxyl, alkoxyl, and amino substituents, for instance, have electron -withdrawing inductive effects because of the electronegativity of the -X, -O, or —N atom bonded to the aromatic ring but have t[ecUou-donating resonance effects because of the lone-pair electrons on those same —X, -O, or —N atoms. When the two effects act in opposite directions, the stronger of the two dominates. 

Meta-directing deactivators Ortho- ajid para-directing deactivators  

Meta-directing deactivators Ortlio- and para-directing deactivators  

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II. Substituent effects in substituted aromatic rings (Sections 16.4 - 16.6). 

Bromination of Aromatic Rings 593 Other Aromatic Substitutions 597 Alkylation of Aromatic Rings The Friedel-Crafts Reaction Acylation of Aromatic Rings 604 Substituent Effects in Substituted Aromatic Rings 605 An Explanation of Substituent Effects 610 Trisubstituted Benzenes Additivity of Effects... 

Substituent Effects in Substituted Aromatic Rings An Explanation of Substituent Effects... 

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