A nitro group (–NO₂) effectively stabilizes a negative charge on an adjacent carbon atom through resonance:

Two of the following nitrophenols are much more acidic than phenol itself. The third compound is only slightly more acidic than phenol. Use resonance structures of the appropriate phenoxide ions to show why two of these anions should be unusually stable.

For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.

d. NHCH₃

e. OCH₃

f. ⁺N(CH₃)₃

Explain why the pK_a of p-nitrophenol is 7.14, whereas the pK_a of m-nitrophenol is 8.39.

For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.

a. Br

b. CH₂CH₃

c.

Which loses a proton more readily: a methyl group bonded to cyclohexane or a methyl group bonded to benzene?

In each pair, choose the most basic compound. Justify your answer.

(d)

In each pair, choose the most acidic compound. Justify your answer. The most acidic proton in each compound has been indicated.

(b)

Which of the following indicated atoms would you expect to be most basic?

(c)

Rationalize the difference in pKₐ values for the two hydroxyl groups.