3. Acids and Bases

Rank the following alcohols from strongest to weakest acid.

CH₂═CHCH₂OH; CH₃CH₂CH₂OH; HC≡CCH₂OH

Rank the following compounds from strongest to weakest acid:

CH₃CH₂OH; CH₃CH₂NH₂; CH₃CH₂SH; CH₃CH₂CH₃

If HCl is a weaker acid than HBr, why is ClCH₂COOH a stronger acid than BrCH₂COOH?

Which is a stronger base?

a.

b.

Which is a stronger acid?

c. CH₃OCH₂CH₂CH₂OHorCH₃CH₂OCH₂CH₂OH

d.

The pK_a of ascorbic acid (vitamin C, page 55) is 4.17, showing that it is slightly more acidic than acetic acid (CH₃COOH, pK_a 4.74).

c. Compare the most stable conjugate base of ascorbic acid with the conjugate base of acetic acid, and suggest why these two compounds have similar acidities, even though ascorbic acid lacks the carboxylic acid (COOH) group.

Rank the following acids in decreasing order of their acid strength. In each case, explain why the previous compound should be a stronger acid than the one that follows it.

The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however.

b. Determine which nitrogen atom is the most basic.

Choose the more basic member of each pair of isomers, and show why the base you chose is more basic.

(a)

(b)

The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red.

b. Explain why X is a stronger acid than W.

c. Explain why Y is a stronger acid than X.

d. Explain why Z is a stronger acid than Y.

Choose the more acidic member of each pair of isomers, and show why the acid you chose is more acidic.

(a)

(b)

(c)

The following compounds can all react as acids.

c. Rank the original compounds in order, from strongest acid to weakest acid.

Consider the type of orbitals involved, and rank the following nitrogen compounds in order of decreasing basicity. 2. Rank the conjugate acids in order of increasing acidity. (Hint: These two orders should be the same!)

Consider each pair of bases, and explain which one is more basic. Draw their conjugate acids, and show which one is a stronger acid.

(a)

(b)

Write equations for the following acid–base reactions. Label the conjugate acids and bases, and show any inductive stabilization. Predict whether the equilibrium favors the reactants or products. Try to do this without using a table of pKa values, but if you need a hint, you can consult Appendix 4.

a. CH₃CH₂OH + CH₃NH⁻

b. F₃CCOONa + Br₃C—COOH

c. CH₃OH + H₂SO₄