3. Acids and Bases

Which species in each of the pairs in Problem 80 is the stronger base?

a.

b.

e. Which has a greater Ka: cyclohexanol or phenol?

f. Which is a stronger acid: cyclohexanol or phenol?

Which member of each pair is the stronger base?

c. phenolate ion or ethoxide ion

d. phenolate ion or acetate ion

Glycine has pK_a values of 2.3 and 9.6. Do you expect the pK_a values of glycylglycine to be higher or lower than these values?

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

(c)

Which is the most acidic compound in each pair?

(a)

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

(a)

Which acid in each pair would you expect to more readily donate a proton to a basic compound?

(a)

Which is the most stable base in each pair?

(b) HS^– and HO^–

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

(a)

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

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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)

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.

(e)

Rank the compounds in each set in order of increasing acid strength.

(c)

Fosamax (shown on the previous page) has six acidic groups. The active form of the drug, which has lost two of its acidic protons, is shown in the box. 

(Notice that the phosphorus atom in Fosamax and the sulfur atom in [Problem 36] can be surrounded by more than eight electrons because P and S are below the second row of the periodic table.)

a. Why are the OH groups bonded to phosphorus the strongest acids of the six groups?

b. Which of the remaining four groups is the weakest acid?