Are the following substituents ortho–para directors or meta directors?
d. COOH
e. CF₃
f. N=O

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Step 1: Understand the concept of substituent effects in electrophilic aromatic substitution reactions. Substituents on a benzene ring can influence the position of incoming groups by either donating or withdrawing electron density. Electron-donating groups are typically ortho–para directors, while electron-withdrawing groups are meta directors.

Step 2: Analyze the functional group COOH (carboxylic acid). The COOH group contains a carbonyl group (C=O) and an -OH group. The carbonyl group is highly electron-withdrawing due to resonance and inductive effects, pulling electron density away from the benzene ring. This makes COOH a meta director.

Step 3: Examine the functional group CF3 (trifluoromethyl). The CF3 group is strongly electron-withdrawing due to the high electronegativity of fluorine atoms, which exert a strong inductive effect. This electron withdrawal reduces electron density on the benzene ring, making CF3 a meta director.

Step 4: Evaluate the functional group N=O (nitroso group). The nitroso group is electron-withdrawing due to resonance and inductive effects, as the nitrogen atom can pull electron density away from the benzene ring through its double bond to oxygen. This makes N=O a meta director.

Step 5: Summarize the findings: COOH, CF3, and N=O are all electron-withdrawing groups, and therefore, they direct incoming substituents to the meta position in electrophilic aromatic substitution reactions.

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Key Concepts

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

Ortho-Para vs. Meta Directors

In electrophilic aromatic substitution, substituents on a benzene ring can influence the position where new substituents are added. Ortho-para directors promote substitution at the ortho and para positions relative to themselves, while meta directors favor substitution at the meta position. Understanding these classifications is crucial for predicting the outcomes of reactions involving aromatic compounds.

Electron-Withdrawing vs. Electron-Donating Groups

Substituents can be classified as electron-withdrawing groups (EWGs) or electron-donating groups (EDGs) based on their effect on the electron density of the aromatic ring. EWGs, such as -COOH and -CF3, typically deactivate the ring and direct substitution to the meta position. In contrast, EDGs increase electron density and direct substitution to the ortho and para positions.

Resonance and Inductive Effects

The behavior of substituents in directing electrophilic substitution can be explained through resonance and inductive effects. Resonance involves the delocalization of electrons, which can stabilize or destabilize intermediates during reactions. Inductive effects arise from the electronegativity of atoms in a substituent, influencing the electron density of the aromatic ring and thus its reactivity and substitution pattern.

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