3. Acids and Bases

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

Which proton, H_a or H_b, would you expect to have the lower pK_a value?

Which is the most stable base in each pair?

(a)

Which is the most acidic compound in each pair?

(b) HF vs. HCl

Which is the most acidic compound in each pair?

(c)

Using qualitative reasoning for the acid–base reactions shown,

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

(ii) Which side of the reaction is favored?

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

(c)

Rank the following alcohols in order of descending pK_a value. Explain your ranking.

The nitrogen screened in purple in Figure 4.43 is not protonated at physiological pH. Why?

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Which is the most stable base in each pair?

(b) HS^– and HO^–

Identify the stronger base in each pair. Explain your choice. Citing pK_a values is not an acceptable answer.

(d)

Imidazole is a heteroaromatic base. Which nitrogen, a or b, is most basic?

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

(b)

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)

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(a)

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(f)