Organic Chemistry: Concepts and Applications - Headley Allan D. 2020

Acid—Base Reactions in Organic Chemistry
End of Chapter Problems

1. 7.15 Arrange the bases shown below in terms of base strengths, i.e. the most basic first (pK_a values of the conjugate acids are shown in parenthesis).

Cl⁻(−7); CH₃O⁻(15.5); F⁻(3.2); CN⁻(9.1)

2. 7.16 For the acids shown below of which the pK_a values are given in parenthesis, answer the following questions.

HCN (9.31); CH₃CH₂OH (15.9); HCl (−7); CH₃COOH (4.75); CH₃NO₂(10.21)

1. Arrange the acids in order of decreasing acidity, i.e. most acidic first.

2. Give the structure of the conjugate base for each acid.

3. Arrange the conjugate bases that you have given in the previous question in order of decreasing basicity, i.e. most basic conjugate base first.

3. 7.17 Of the following acids, of which pK_a values of the acids are shown in parenthesis, determine which has the weakest conjugate base? Explain your answer.

HF (2.55); H₂O (15.9); HCN (9.31); HI (−9.5)

4. 7.18 Without the aid of a pK_a table, determine which of the following two acids is the strongest acid: ClCH₂COOH and FCH₂COOH, explain your answer.

5. 7.19 Of the pairs of acids shown below, which is the strongest acid, briefly explain your answer?

6. 7.20 Consider the molecules shown below, then answer the following questions.

1. For each molecule, remove the most acidic hydrogen and draw the structure of the resulting conjugate base.

2. For each of the conjugate base that you have drawn, give as many resonance structures as you can.

3. Of the resonance structures that you have drawn in the above question, determine which contributes the most to the overall structure of each conjugate base.

7. 7.21 For each of the following sets of compounds, indicate which is the weaker base and give a brief explanation for your choice.

1. CH₃COO⁻; ClCH₂COO⁻; Cl₂CHCOO⁻; CCl₃COO⁻

2. Cl⁻; CN⁻; CH₃O⁻; CH₃⁻

3. OH⁻; CN⁻; Br⁻; NH₂⁻

8. 7.22 For the reactions shown below, which is the Lewis acid and which is the Lewis base?

9. 7.23 Naringenin is a flavonoid, which has many hydrogens. The structure of Naringenin is shown below. Identify all hydrogens and determine their relative acidities.

10. 7.24 Complete the following reactions for supplying the products, the solvent for each reaction is shown below the arrow.

11. 7.25 Organometallic reagents, such as the Grignard reagent, are extremely strong bases, and extreme care must be used in the selection of an appropriate solvent when using these reagents. For example, protic solvents, such as alcohols, are not good solvents since they are readily deprotonated in the presence of an organometallic reagent. Tetrahydrofuran is a good solvent when using these reagents, yet a very similar reagent, 2,2,5,5-tetramethyltetrahydrofuran, is a poor solvent. Explain this observation.