The C=O double bond has a dipole moment of about 2.4 D and a bond length of about 1.23 Å.

a. Calculate the amount of charge separation in this bond.

The C=O double bond has a dipole moment of about 2.4 D and a bond length of about 1.23 Å.

b. Use this information to evaluate the relative importance of the following two resonance contributors:

The N—F bond is more polar than the N—H bond, but NF₃ has a smaller dipole moment than NH₃. Explain this curious result.

NF₃

μ= 0.2 D

NH₃

μ = 1.5 D

1. Draw the Lewis structure.

2. Show how the bond dipole moments (and those of any nonbonding pairs of electrons) contribute to the molecular dipole moment.

3. Estimate whether the compound will have a large, small, or zero dipole moment.

d. CH₃F

e. CF₄

f. CH₃OH

1. Draw the Lewis structure.

2. Show how the bond dipole moments (and those of any nonbonding pairs of electrons) contribute to the molecular dipole moment.

3. Estimate whether the compound will have a large, small, or zero dipole moment.

g. HCN

h. CH₃CHO

i. H₂C=NH

Two isomers of 1,2-dichloroethene are known. One has a dipole moment of 2.4 D; the other has zero dipole moment. Draw the two isomers, and explain why one has zero dipole moment.

CHCl=CHCl 1,2-dichloroethene

Draw the hydrogen bonding that takes place between

a. two molecules of ethanol.

b. two molecules of propylamine.

Draw the hydrogen bonding that takes place between

c. a molecule of dimethyl ether and two molecules of water.

d. two molecules of trimethylamine and a molecule of water.

For each pair of compounds, circle the compound you expect to have the higher boiling point. Explain your reasoning.

a. (CH3)3C—C(CH₃)₃ or (CH₃)₂CH—CH₂CH₂—CH(CH₃)₂

b. CH₃(CH₂)₆CH₃ or CH₃(CH₂)₅CH₂OH

c. CH₃CH₂OCH₂CH₃ or CH₃CH₂CH₂CH₂OH

For each pair of compounds, circle the compound you expect to have the higher boiling point. Explain your reasoning.

(d) HOCH₂—(CH₂)₄—CH₂OH or (CH₃)₃CCH(OH)CH₃

(e) (CH₃CH₂CH₂)₂NH or (CH₃CH₂)₃N

(f)

Circle the member of each pair that is more soluble in water.

a. CH₃CH₂OCH₂CH₃ or CH₃CH₂CH₂CH₂CH₃

b. CH₃CH₂OCH₂CH₃ or CH₃CH₂CH₂OH

c. CH₃CH₂NHCH₃ or CH₃CH₂CH₂CH₃

d. CH₃CH₂OH or CH₃CH₂CH₂CH₂OH

e.

Calculate the pH of the following solutions.

a. 5.00 g of HBr in 100 mL of aqueous solution

b. 1.50 g of NaOH in 50 mL of aqueous solution

Ammonia appears in [TABLE 2-2 ] as both an acid and a conjugate base. a. Explain how ammonia can act as both an acid and a base. Which of these roles does it commonly fill in aqueous solutions?

b. Show how water can serve as both an acid and a base.

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.

Write equations for the following acid–base reactions. Use the information in Table 2-2 or Appendix 4 to predict whether the equilibrium will favor the reactants or the products.

a. HCOOH + ^–CN

b. CH₃COO^– + CH₃OH

c. (CH₃)₂CHOH + NaNH₂

Ethanol, methylamine, and acetic acid are all amphoteric, reacting as either acids or bases depending on the conditions.

a. Rank ethanol, methylamine, and acetic acid in decreasing order of acidity. In each case, show the equation for the reaction with a generic base (B:⁻) to give the conjugate base.

Ethanol, methylamine, and acetic acid are all amphoteric, reacting as either acids or bases depending on the conditions.

b. Rank ethanol, methylamine, and acetic acid in decreasing order of basicity. In each case, show the equation for the reaction with a generic acid (HA) to give the conjugate acid.

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pK_a, or estimate them.

a. CH₃Li + H—C≡C—H → CH₄ + H—C≡CLi

b. CH₃Li + (CH₃)3C—OH → CH₄ + (CH₃)₃C—OLi

For each of the following reactions, suggest which solvent(s) would be compatible with the acids and bases involved. (We will ignore any other possible reactions for now.) Your choices of solvents are pentane, diethyl ether, ethanol, water, and ammonia. Refer to Appendix 4 for any needed values of pK_a, or estimate them. 

c.

d.

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

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 pK_a values, but if you need a hint, you can consult Appendix 4.

g. NaOCH₂CH₃ + Cl₂CHCH₂OH

h. H₂Se + NaNH₂

i. CH₃CHFCOOH + FCH₂CH₂COO^–

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.

j. CF₃CH₂O^– + FCH₂CH₂OH

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.

Like nitrogen and carbon, oxygen also shows this same hybridization effect on acidity. Both of the following compounds can lose a proton from a positively charged oxygen with three bonds to give a conjugate base containing a neutral oxygen with two bonds. One of these structures has pK_a = −2.4, while the other has pK_a = −8.0.

a. Show the reaction of each compound with water.

b. Match each structure with its pK_a, and explain your choice.

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!)

Give the structures of their conjugate acids, and estimate their pK_as from similar compounds in Appendix 4.

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)

Which is a stronger base: ethoxide ion or acetate ion? Give pK_b values (without looking them up) to support your choice.

Acetic acid can also react as a very weak base (pK_b = 20). Two different sites on acetic acid might become protonated to give the conjugate acid. Draw both of these possible conjugate acids, and explain (resonance) why the correct one is more stable. Calculate the pK_a of this conjugate acid.

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

(a)

(b)

(c)