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e) Phenol (left) is a stronger acid than aniline (right) because the H on the more electronegative is more acidic than the H on the less electronegative N. 4.20 a) The compound on the right is a weaker base because the nitro group stabilizes the unshared electron pair on the N by both its electron- withdrawing inductive effect and resonance. b) The anion on the left is the weaker base because it has a larger resonance stabilization (two additional resonance structures) than does the anion on the right (one additional resonance structure). 4.21 Remember, the equilibrium favors the formation of the weaker acid and the weaker base. The larger the pKₐ , the weaker the acid. a) Ammonia = 38) is a weaker acid than a ketone = 20), so the equilibrium favors the products. b) Dimethylsulfoxide = 38) is a weaker acid than an alcohol = 16), so the equilibrium favors the products. c) HCI = -7) is a much stronger acid than phenol = 10), so the equilibrium favors the reactants. 4.22 The solvent must not be acidic enough to protonate the anion. The pKₐ of the conjugate acid of the anion is 25, so the solvent must have a pKₐ larger than 25. a) acceptable because the pKₐ of NH₃ is 38 b) not acceptable because the pKₐ of an alcohol is 16 c) acceptable because an ether has no H with a pKₐ approaching 25 4.23 To get the conjugate acid, use the most basic pair of electrons to form a bond to a proton. + NH₃ :OH + a) b) c) d) CH₃C=CH e) NH 54