The following compounds can all react as acids.

a. For each compound, show its conjugate base. Show any resonance forms if applicable.

A naturally occurring amino acid such as alanine has a group that is a carboxylic acid and a group that is a protonated amine. The pK_a values of the two groups are shown.

e. Is there a pH at which alanine is uncharged (that is, neither group has a charge)?

f. At what pH does alanine have no net charge (that is, the amount of negative charge is the same as the amount of positive charge)?

For each of the following compounds, draw the form that predominates at pH = 3, pH = 6, pH = 10, and pH = 14:

c. CF₃CH₂OH (pK_a = 12.4)

Give the structures of their conjugate acids, and estimate their pK_as from similar compounds in Appendix 4.

Ammonia appears in [TABLE 2-2] as both an acid and a conjugate base.

d. Show how methanol (CH₃OH) can serve as both an acid and a base. Write an equation for the reaction of methanol with sulfuric acid.

Oxidation of a primary alcohol to an aldehyde usually gives some over-oxidation to the carboxylic acid. Assume you have used PCC to oxidize pentan-1-ol to pentanal.

(a) Show how you would use acid–base extraction to purify the pentanal.

(b) Which of the expected impurities cannot be removed from pentanal by acid–base extractions? How would you remove this impurity?

The boiling points of hex-1-ene (64 °C) and hex-1-yne (71 °C) are sufficiently close that it is difficult to achieve a clean separation by distillation. Show how you might use the acidity of hex-1-yne to remove the last trace of it from a sample of hex-1-ene.

The following compounds can all react as bases.

a. For each compound, show its conjugate acid. Show any resonance forms if applicable.

Predict the products of the following acid–base reactions.

(g) HCOOH + CH₃O^– ⇌

(h) ⁺NH₃CH₂COOH + 2 ^–OH ⇌