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)

In the following reactions,

(i) identify the acid and base,

(ii) identify the most electron-rich atom in the base,

(iii) identify the most acidic hydrogen in the acid,

(iv) provide an arrow-pushing mechanism of the proton transfer that will occur, and

(v) predict the product of the reactions. [You'll need to provide the lone pairs here.]

(d) H₂O + HCl ⇌

Triosephosphate isomerase (TIM) catalyzes the conversion of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate. The enzyme’s catalytic groups are Glu 165 and His 95. In the first step of the reaction, these catalytic groups function as a general-base and a general-acid catalyst, respectively. Propose a mechanism for the reaction.

What products are formed when each of the following reacts with HO⁻?

c. CH₃N⁺H₃

d. BF₃

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)?

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.

The following compounds can all react as acids.

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

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?