Activation or Deactivation by Substituents on a Benzene Ring

In Section 14-8 we discussed the effect that substituents have on the efficiency of the Diels-Alder reaction Electron donors on the diene and acceptors on the dienophile are beneficial to the outcome of the cycloaddition. Chapter 15 revealed another manifestation of these effects Introduction of electron-withdrawing substituents into the benzene ring (e.g., as in nitration) caused further electrophilic aromatic substitution (EAS) to slow down, whereas the incorporation of donors, as in the Friedel-Crafts alkylation, caused substitution to accelerate. What are the factors that contribute to the activating or deactivating nature of substituents in these processes How do they make a monosubstituted benzene more or less susceptible to further electrophilic attack  

Inductive Effects of Some Substituents on the Benzene Ring 

Finally, groups bearing a polarized double or triple bond, whose positive (5 ) end is attached to the benzene nucleus, such as carbonyl, cyano, nitro, and sulfonyl, are electron withdrawing through resonance. 

Note that, here, resonance reinforces induction. 

Electrostatic potential maps indicate the presence of electron-donating substituents by depicting the benzene ring as shaded relatively red electron-withdrawing groups make the benzene ring appear shaded relatively blue (green). 

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