Specify which in each pair is the harder Lewis acid. Justify your choice beyond just looking at Table 20.2.
(c) Mg²⁺ vs. Na⁺

Using the convention that the acid and base are on the left side of the chemical equation, label the acid, base, conjugate acid, and conjugate base in the following reactions.

(b)

In comparison to CH₃^- in Assessment 2.86, the related molecule BH₄^- is itself not a Lewis base at boron. Why?

Design an acid–base extraction scheme to separate a mixture of the basic amine N,N-dimethylaniline and naphthalene.

If a base has a conjugate acid with a high pK_a value, is it stable or unstable? How do you know this is true (besides 'I just remember')?

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)?