3. Acids and Bases

Imidazole is a heteroaromatic base. Which nitrogen, a or b, is most basic?

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

(b)

Using qualitative reasoning for the acid–base reactions shown,

(i) which is stronger, the acid or the conjugate acid?

(ii) Which side of the reaction is favored?

(iii) Would you expect a K_eq greater than, equal to, or less than 1?

(b)

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(a)

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(f)

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.]

(b)

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.]

(d)

Which acid in each pair would you expect to more readily donate a proton to a basic compound?

(a)

Why is the pK_a value of protonated hydroxylamine (6.0) so much lower than the value of a protonated primary amine such as protonated methylamine (10.7)?

In light of your answers to Assessments 24.54 and 24.55, rank the following based on the rate of protonation of the alkene (1 = most basic, 6 = least basic). [Ignore the fact that the alkene may not be the most basic site in the molecule.]

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?

Which is the most stable base in each pair?

(c) NH₃ vs. H₂O

Explain why a base can remove a proton from the α-carbon of N,N-dimethylethanamide but not from the α-carbon of either N-methylethanamide or ethanamide.

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

a. The first pK_a (for the COOH group in the center of the molecule) is lower than the pK_a of acetic acid.

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