3. Acids and Bases

The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however.

b. Determine which nitrogen atom is the most basic.

Given the following compounds: $\mathrm{CH}{3}_3\mathrm{COH}$ (tert-butanol), $\mathrm{CH}{3}_2\mathrm{CHOH}$ (isopropanol), and $\mathrm{CH}{3}_2\mathrm{CH}\mathrm{OH}$ (ethanol), rank them in order of increasing acidity.

p-Nitrophenol (pK_a = 7.2) is ten times more acidic than m-nitrophenol (pK_a = 8.4) Explain.

Methyllithium (CH₃Li) is often used as a base in organic reactions.

b. What is the conjugate acid of CH₃Li? Would you expect CH₃Li to be a strong base or a weak base?

Four pairs of compounds are shown. In each pair, one of the compounds reacts more quickly, or with a more favorable equilibrium constant, than the less conjugated system. In each case, explain the enhanced reactivity.

(d)

Which member of each pair is the stronger base?

a. ethylamine or aniline

b. ethylamine or ethoxide ion

Using qualitative reasoning for the acid–base reactions shown,

(i) which is stronger, the acid or the conjugate acid?

(ii) Which side of the reaction is favored?

(iii) Would you expect a K_eq greater than, equal to, or less than 1?

(b)

A carboxylic acid ( pK_a = 5) is 10¹¹ times more acidic than an alcohol (pK_a = 16). Why?

Without using pK_a values, pick out the least reactive (most stable) base in each pair. Explain your answer.

(a)

Rank the following compounds from strongest to weakest acid:

CH₃CH₂OH; CH₃CH₂NH₂; CH₃CH₂SH; CH₃CH₂CH₃

Rationalize the rather large difference in pK_a values for the two carboxylic acids shown.

The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red.

b. Explain why X is a stronger acid than W.

c. Explain why Y is a stronger acid than X.

d. Explain why Z is a stronger acid than Y.

Which is a stronger acid?

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d. CH₃CH₂CH₂OH or CH₃CH₂CH₂SH

Given the following compounds: ${\mathrm{CH}}_3\mathrm{COOH}$, ${\mathrm{CH}}_3\mathrm{OH}$, and ${\mathrm{NH}}_3$, rank them in order of decreasing acidity.

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