3. Acids and Bases

Which is the most stable base in each pair?

(a)

Explain why pyrrole (pK_a ~ 17) is a much stronger acid than ammonia (pK_a = 36).

The following compounds can all react as bases.

b. Rank the conjugate acids in the order you would predict, from most stable to least stable.

Consider the following drugs used to treat the indicated diseases. Would you expect the activity of these drugs to be impacted by a patient taking other medicines for acid reflux disease?

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

(b) CH₃CH₂CH₂CHBrCOOH, CH₃CH₂CHBrCH₂COOH, CH₃CHBrCH₂CH₂COOH

Which anion in each pair would you expect to react more quickly with H⁺?

(b)

Without using pK_a values, pick out the more acidic compound in each pair. Explain your answer.

(a)

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

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

(b)

Acetylacetone (pentane-2,4-dione) reacts with sodium hydroxide to give water and the sodium salt of a carbanion. Write a complete structural formula for the carbanion, and use resonance forms to show the stabilization of the carbanion.

Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.]

(a)

Which is the most acidic compound in each pair?

(b) HF vs. HCl

Which of the following amino acid side chains can help remove a proton from the α-carbon of an aldehyde?

Which is the most stable base in each pair?

(c) NH₃ vs. H₂O