For each horizontal row of substituted benzenes, indicateb. the one that is the least reactive in an electrophilic aromatic substitution reaction.

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Identify the substituents on each benzene ring.

Determine the electronic effects of each substituent: whether they are electron-donating or electron-withdrawing.

Recall that electron-donating groups (EDGs) activate the benzene ring towards electrophilic aromatic substitution, while electron-withdrawing groups (EWGs) deactivate it.

Compare the substituents: the benzene with the strongest electron-withdrawing group will be the least reactive.

Select the benzene with the most deactivating substituent as the least reactive in electrophilic aromatic substitution.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrophilic Aromatic Substitution (EAS)

Electrophilic Aromatic Substitution is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This reaction is crucial for synthesizing various aromatic compounds. The reactivity of the aromatic compound is influenced by the nature of substituents already present on the ring, which can either activate or deactivate the ring towards further substitution.

Activating and Deactivating Groups

Substituents on a benzene ring can be classified as activating or deactivating based on their electronic effects. Activating groups, such as -OH or -NH2, donate electron density to the ring, increasing its reactivity towards electrophiles. In contrast, deactivating groups, like -NO2 or -CF3, withdraw electron density, making the ring less reactive in EAS reactions. Understanding these effects is essential for predicting the reactivity of substituted benzenes.

Ortho/Para vs. Meta Directing

The position of substituents on a benzene ring affects the orientation of subsequent electrophilic substitutions. Activating groups are typically ortho/para directing, meaning they favor substitution at the ortho or para positions relative to themselves. Deactivating groups, however, are usually meta directing, leading to substitution at the meta position. This distinction is important for determining the least reactive substituted benzene in EAS reactions.

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