1. Chapter 7
Acids and Bases;
Intermolecular Attractions

2. Read (no lecture) Section 7.11, 7.12 and 7.13
Problems for Chapter 7
Skip section 7.4, 7.10, and 7.14
Read (no lecture) Section 7.11, 7.12 and 7.13
In Text: 1 a, b, g, h, 2b, 6b, 8a, 11b, c
14, 15, 18 through 22
24, 25, 27, 28, 31, 32, 33, 34
End of Chap: 36, 38, 42, 43, 45 a, b, e,
48 through 52 54, 55, 56, 58, 59,
62, 63

3. HA + B- A- + BH Section 7.1 Bronsted-Lowry Theory acid = proton donor
conjugate
base
conjugate
acid
acid
base
HA B A BH
-H+
+H+
acid = proton donor
base = proton acceptor
Conjugate Acid = Base + Proton
Conjugate Base = Acid - Proton

4. Section 7.2 pKa
pKa = - log Ka
Strong acid = large Ka = small pKa
Weak acid = small Ka = large pKa

5. Sect. 7.2 Relative Acid and Base Strengths

6. Acid Strengths
Strong Acid
Conjugate base is weak
pKa is small
Weak Acid
Conjugate base is strong
pKa is large

7. B: A Section 7.3: Lewis Acid-Base theory
more general than Bronsted theory
BASE B:
electron-pair donor A
ACID
electron-pair acceptor
Some Lewis Acids:
Fe3+ BF3 H3O+
NH3 H2O
Some Lewis Bases:

8. Section 7.5
Electronegativity and Size Effects

9. Sect. 7.5: Electronegativity and Size

10. Effect of Atomic Size on Acidity
increasing
atom size
pKa Values
3.5 16 5 -7 7 -9 4
-10 3 I - Br - F - Cl -
1.36 A
1.81 A
1.95 A
2.16 A

11. Effect of Electronegativity on Acidity
increasing
electronegativity
pKa Values
>45 45 20 34 35 15 16 18 5
3.5

12. Section 7.6
Resonance Effects

13. Take Away Lession: Resonance strengthens acid Resonance weakens base

14. Resonance in the Acetate Ion
equivalent structures
charge on oxygens O C H C 3 O + O -H _ C H C O H 3
base _
acetic acid O C H C 3 O
acetate ion

15. - _ _ Phenolate ion Resonance O non-equivalent structures
charge on carbon and oxygen

16. Nitrophenols Placing a nitro group on the benzene ring
of a phenol increases its acidity.
The effect is largest when the nitro group
is placed in an ortho or a para position on
the ring, and considerably smaller for the
meta position.
Multiple nitro groups at the ortho and para
positions can increase the pKa of a phenol
to the point that it becomes a very strong
acid.

17. pKa Values of Nitrophenols
7.2 10
9.3
4.0
0.4
7.3

18. _ _ Resonance in p-Nitrophenol O N extra structure When in an ortho
or para position
a nitro group can
participate in
resonance. _ O N 2 +
extra
structure +

19. Section 7.7
Alpha Hydrogen
compounds

21. Take Away Lession: Resonance strengthens acid Resonance weakens base

22. Section 7.8
Inductive Effects

23. Resonance operates through the p bonding system
Resonance operates through the p bonding system. It doesn’t drop off with distance.
Inductive effect operates through the sigma bonding system. It drops off with increasing distance.

24. Cl d- d+ C d+ d- CH3 C Types of Inductive Effects R, CH3
ELECTRON
WITHDRAWING
GROUPS
ELECTRON
DONATING
GROUPS Cl d- d+ C d+ d-
CH3 C
R, CH3
F, Cl, Br, NO2 , NR3+
electronegative elements
take electron density
from cabon. This
strenthens the acidity.
alkyl groups donate electron
density to carbon. This weakens
the acidity.

25. O d- d+ Cl C O O d- d+ Cl C C C O Inductive Effects on Haloacids d- d+
Chlorine helps
to stabilize -CO2-
by withdrawing
electrons Cl C O O d- d+ d- d+ d- d+ Cl C C C O
The effect diminishes with distance
- it carries for about 3 bonds.

26. Inductive Effects pKa Values 3.13 4.75 2.87 2.81 2.81 1.29 2.66 0.65
increasing
electronegativity
multiple
substituents
pKa Values
3.13
4.75
2.87
2.81
2.81
1.29
2.66
0.65

27. Inductive Effects pKa Values 3.75 4.8 4.5 4.75 4.0 4.87 4.81 2.9 5.02
distance
5.02
When the chlorine atom is moved
further away from the carboxyl group,
acidity decreases
Alkyl groups release electrons.
This decreases acidity

28. Section 7.9
Hybridization Effects

29. Effect of Hybridization
pKa values
sp3
ca. 50
sp orbitals are more electron withdrawing than sp3 orbitals (sp orbitals have more s character).
sp > sp2 > sp3
sp2 35 sp 25

30. Section 7.11
Solvent Effects

31. Solvation Effects - 4.75 5.02 4.87 4.81 C H C O O H C O H C H C H C O3 3
5.02 C H C H C O O H
4.87 3 2 C H C H C H C O O H
4.81 3 2 2
Notice that these are all similar
….but this one has a larger pKa
This is probably a solvation effect.
Solvation lowers the energy of the ion.
steric hindrance C O - H
Stronger
Acid
The bulky
t -butyl group
is not as well
solvated.
unbranched
Weaker
Acid

32. Sect. 7.12: Intermolecular Attractions
hydrogen bonding
dipole-dipole attractions
London forces or van der Waals attractions
Sect. 7.13: Solubility

33. SUMMARY

34. Electronegativity of atom bearing acidic hydrogen; more electronegative = more acidic
Size of atom bearing acidic hydrogen; larger = more acidic.
Resonance: greater charge delocalization in conjugate base = more acidic.
alpha-hydrogens: carbonyls, nitro, cyano, etc. Greater charge delocalization in conjugate base = more acidic.
Inductive effect: electronegative atoms withdraw electrons making the acid more acidic.
Hybridization; more s-character = more acidic

35. Classification of Weak and Strong Acids by Functional Group
weak acids
strong acids
pKa
di- and tri-
nitrophenols
alkanes
alkenes
amines
alcohols
ketones
amides
alkynes
phenols
carboxylic
acids
nitrophenols
inorganic
acids
oxyacids
b-diketones

36. Electron-Withdrawing Effects Strengthen Acids
(-)
(-) - - - - -
Any effect that “bleeds” electron density away from
the negatively-charged end of the conjugate base will
stabilize (lower the energy) of the conjugate base and
make it a weaker base.
The parent acid will be a stronger acid.

37. Electron-Donating Effects Weaken Acids
Conversely …..
Electron-Donating Effects
Weaken Acids -
(-)
(-) - - - - -
Any effect that “pushes” extra electron density toward
the negatively-charged end of the conjugate base will
destabilize (increase the energy) of the conjugate base
and make the base weaker. The parent acid will be
stronger.