3. Acids and Bases

a. Which is a stronger base: CH₃COO⁻ or HCOO⁻? (The pK_a of CH₃COOH is 4.8; the pK_a of HCOOH is 3.8.)

b. Which is a stronger base: HO⁻ or ^-NH₂? (The pK_a of H2O is 15.7; the pK_a of NH3 is 36.)

c. Which is a stronger base: H₂O or CH₃OH? (The pK_a of H3O+ is −1.7; the pK_a of CH₃O⁺H₂ is −2.5.)

A medicinal chemist needed to deprotonate acetylene ( HC≡CH ) for use in a coupling reaction. Among the options given, which base(s) could be used for this process?

For each compound, indicate the atom that is most apt to be protonated.

a.

b.

c.

Rank the following from strongest base to weakest base:

b.

Citrus fruits are rich in citric acid, a compound with three COOH groups. Explain the following:

b. The third pK_a is greater than the pKa of acetic acid.

Given the structure of ascorbic acid (vitamin C):

(a) Is ascorbic acid a carboxylic acid?

(b) Compare the acid strength of ascorbic acid (pK_a = 4.71) with acetic acid.

Which is a stronger base: ethoxide ion or acetate ion? Give pK_b values (without looking them up) to support your choice.

Given the structure of ascorbic acid (vitamin C):

(c) Predict which proton in ascorbic acid is the most acidic.

(d) Draw the form of ascorbic acid that is present in the body (aqueous solution, pH = 7.4)

Arrange the following compounds in order of decreasing acidity.

CH₃COOH, CH₃OH, CH₃CH₃, CH₃SO₃H, CH₃NH₂, CH₃SH, CH₃C≡CH

Why is imidazole a stronger acid (pK_a ~ 14.4) than pyrrole (pK_a ~ 17)?

The K_a of phenylacetic acid is 5.2 × 10⁻⁵, and the pK_a of propionic acid is 4.87.

a. Calculate the pK_a of phenylacetic acid and the K_a of propionic acid.

b. Which of these is the stronger acid? Calculate how much stronger an acid it is.

Estimate the K_eq for the following reactions based on the stability of the anions involved.

(a)

Does methanol behave as an acid or a base when it reacts with methylamine?

Which of the following bases can remove a proton from a terminal alkyne in a reaction that favors products?

You are planning to carry out a reaction that produces protons. The reaction will be buffered at pH = 10.5. Would it be better to use a protonated methylamine/methylamine buffer or a protonated ethylamine/ethylamine buffer? (pK_a of protonated methylamine = 10.7; pK_a of protonated ethylamine = 11.0)