Organic Chemistry, An Acid-Base Approach
3rd Edition Michael B. Smith
Table of Contents:-
Chapter 1: Introduction
Chapter 2: Why Is an Acid-Base Theme Important?
Chapter 3: Bonding
Chapter 4: Alkanes, Isomers, and an Introduction to Nomenclature
Chapter 5: Functional Groups
Chapter 6: Acids, Bases, and Nucleophiles
Chapter 7. Chemical Reactions, Bond Energy, and Kinetics
Chapter 8: Conformations
Chapter 9: Stereoisomers: Chirality, Enantiomers, and Diastereomers
Chapter 10: Acid– -Bonds: Addition Reactions
Chapter 11: Substitution Reactions
Chapter 12: Elimination and p-Bond-Forming Reactions
Chapter 13: Spectroscopic Methods of Identification
Chapter 14: Organometallics
Chapter 15: Oxidation
Chapter 16: Reactions of Aldehydes and Ketones
Chapter 17: Reduction
Chapter 18: Carboxylic Acid Derivatives and Acyl Substitution
Chapter 19: Aromatic Compounds and Benzene Derivatives
Chapter 20: Enolate Anions: Acyl Addition and Acyl Substitution
Chapter 21: Difunctional Molecules: Dienes and Conjugated Carbonyl Compounds
Chapter 22. Difunctional Molecules: Pericyclic Reactions
Chapter 23: Heteroaromatic Compounds
Chapter 24: Multifunctional Compounds: Amines, Amino Acids and Peptides
Chapter 25: Multifunctional Compounds: Carbohydrates
,Chapter 01: No Solutions Available
Chapter 02: Why Is an Acid-Base Theme Important?
22. (a)
O O
H
N O OH2 N O H3O+
O O
Ka = [NO3–] [H3O+]
[HNO3] [H2O]
Nitric acid is a stronger acid than water, so water is the base and nitric acid is the acid in this
reaction to generate the nitrate anion (conjugate base) and the hydronium ion (conjugate acid).
(b)
H H H
NH3 O H-NH3
O
Ka = [HO–] NH4+]
[H2O] [NH3]
Water is a stronger acid than ammonia, so ammonia is the base and water is the acid in this
reaction. The reaction products are hydroxide anion (conjugate base) and the ammonium ion
(conjugate acid).
(c)
Br H-NH3
Br H
NH3
Ka = [Br–] [NH4+]
[HBr] [NH3]
Hydrobromic acid is a stronger acid than ammonia, so ammonia is the base and HBr is the acid
in this reaction to generate the bromide anion (conjugate base) and the ammonium ion (conjugate acid).
(d)
Cl H OH2 Cl- H3O+
[Cl -] [H 3O+]
Ka =
[HCl] [H 2O]
Hydrochloric acid is a stronger acid than water, so water is the base and HCl is the acid in this
reaction to generate the chloride anion (conjugate base) and the hydronium ion (conjugate acid).
(e)
, Cl Cl
Cl C NH3
Cl C H
Cl NH2 Cl
Na
Ka = [CCl3–] [NH3]
[HCCl3] NaNH2]
Note that the acidic hydrogen atom in chloroform is attached to a carbon atom. The amide
anion is clearly a base, and it a strong base. The strong base reacts with the weakly acidic “carbon
acid”. In other words, NH2– is the base and chloroform is the acid in this reaction that generates the
anion –CCl3 (the conjugate base) and ammonia, NH3, which is the conjugate acid.
23. It is likely due to the relative size of the conjugate bases, the bromide ion and the chloride ion. The
size of the bromide ion is 182 pm or 1.82 Å and that of the chloride ion is 100 pm, or 1.00 Å. Since the
bromide ion is larger there is greater charge dispersal that leads to greater stability of that conjugate
base, so it is less able to donate electrons and it is a weaker base. Therefore, there is a larger Ka for the
reaction of HBr and a base In addition, the larger size of the bromine atom leads to a longer H—Br
bond length relative to H—Cl, and so the H—Br bond is easier to break, which also leads to an
enhancement of the acidity of HBr relative to HCl.
24.
[H3O+] [Cl-]
Ka =
[HCl]
In this reaction, water is the base that reacts with the HCl. Water is used as a solvent and as a
base, so it is also a reactant. The concentration of water that reacts relative to the concentration due to
the large volume of water is minute, so omitting the water concentration term from the Ka equation will
introduce an insignificant error.
25. (a) NH3 (b) CH3CH2CH2O– (c) –HSO4 v (d) I– (e) –:NH2 (f) –CH3
26. In the neutral molecules, arsine (AsH3) and ammonia (NH3), arsenic is larger than nitrogen, with
covalent radii of 119 pm for arsenic and 71 pm for nitrogen (1.19 Å and 0.71 Å), respectively. The
electron density on arsenic is therefore dispersed over a larger area and therefore less available for
donation. Since it is smaller, the charge density of nitrogen is greater which suggests that ammonia is a
stronger Lewis base than arsine. However, arsenic is less electronegative than nitrogen (2.2 versus
3.0), which suggests that arsenic is better able to donate electrons and therefore a stronger Lewis base.
Since N and As are in the same Group 15, the size of the atoms is expected to play a major role and
electronegativity a minor role, which is consistent with ammonia as the stronger base.
27. Sulfur and phosphorus are in the same row of the periodic table so differences in electronegativity
are assumed to be more important than differences in the size of the atoms (P is 195 pm and S is 100
pm). The electronegativity of sulfur is 2.6 and that of phosphorous is 2.2. The conjugate base of SH2 is
-SH and the conjugate base of PH3 is -PH2. Since the sulfur in the -SH anion is more electronegative it
is less likely to donate electrons and it is a weaker base in a reaction with the conjugate acid, which
, leads to a larger Ka. Since phosphorus in the -PH anion is less electronegative it is a stronger base and
reacts better with the conjugate acid, which leads to a smaller Ka. Therefore, H2S is the stronger acid.
28. (a) CH3OH is the strongest acid in this series. The O—H bond is more polarized and easier to
break, and the methoxide anion, H3CO-, is more stable than the anions from CH4 or CH3NH3. NaF
does not have an acidic proton, and it is not a Brønsted-Lowry acid.
(b) The size of the conjugate base increases from fluoride towards iodide, so the charge on the iodide
ion is dispersed over a larger area, which makes it less likely to donate electrons and a weaker
conjugate base. Therefore the iodide is more stable than the other halide ions. This means that Ka is
larger for HI and decreases going towards HF. In other words, HI is the stronger acid. In addition, the
iodine atom is much larger so the H—I bond is longer, and weaker, and it is easier to break relative to
the others.
29.
O H O O O
N O + BASE H—BASE + N O N O N O
O O O O
As shown, nitric acid generates the resonance stabilized nitrate anion. In the nitrate anion, the
charge is dispersed over several atoms, which makes it more difficult for that species to donate electrons
to an acid. In the hydroxide ion, HO-, the charge is concentrated (localized) on the oxygen atom, so it
can donate electrons more easily. Hydroxide is more basic.
30. The fluoride ion is more basic relative to the bicarbonate ion because bicarbonate is resonance
stabilized with the three resonance contributors shown in the figure so the charge is more dispersed.
Therefore, it is much more difficult for bicarbonate to donate electrons and it is a weaker conjugate
base. The charge is concentrated (localized) on fluoride ion so it can donate electron more easily and is
the stronger base.
O O O
C C C
O O O O O O
Resonance Contributors of the Bicarbonate Anion
31. Determine the pKa for each of the following.
(a) Ka = 1.45x105 (b) Ka = 3.6x10–12 (c) Ka = 6.7x10–31 (d) Ka = 18 (e) Ka = 3.8x1014
pKa = -log10 Ka. (a) -5.16 (b) 11.44 (c) 30.17 (d) -1.26 (e) -14.6
32. The most acidic acid will have the smallest pKa. Of this series, HCl is the strongest acid (pKa -7)
relative to HF (pKa 3.17). Water has a pKa of 15.7 and ammonia has a pKa of about 25. Clearly, HCl
is the most acidic and has the smallest pKa.
