1. Acid-Base Chemistry K a is the equilibrium constant for the dissociation of an acid into H + and its conjugate base. Ka values are typically measure in water. acidbase conjugate base conjugate acid We define pK a = -logK a just as pH = -log[H 3 O + ] Weak acids have small K a and large pK a values Strong acids have large K a and small pK a values Remember – when comparing acids, the weaker acid will have…the stronger conjugate base. HA and A - are a conjugate acid-base pair. HB + and B: are also a conjugate acid-base pair. 1

2. A Brønsted acid is simply an electrophile that loses H + to a base. The acidic site is the hydrogen atom. A Brønsted base is simply a nucleophile that makes a bond to the hydrogen atom of an acid. The basic site is the atom/bond donating the electrons used to make this bond. 2

3. AcidKaKapKapKa HClO 410 -10 HF7.2 x 10 -4 3.1 NH 4 + 6.3 x 10 -10 9.2 H2OH2O2.0 x 10 -16 15.7 H2H2 10 -35 35 some typical pK a values Acid-Base Chemistry 3

4. So, for an equilibrium between two conjugate acid/base pairs, the equilibrium will always favour the side which has…the weakest acid. What does this mean for ‘real life chemistry’? So, if you wanted this equilibrium to be product favoured, you would use a base…whose conjugate acid was weaker than phenol. 4

5. Table 5.1 (page 144) In water, there can be no acid stronger than…H 3 O + …and no base stronger than… - OH 5

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7. Pi Bonds… 7

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11. These effects are…additive. These effects…drop off rapidly with increasing number of bonds. 11

12. pK a + pK b for a conjugate acid/base pair = 14 Bases Although potentially confusing, when evaluating base strength we often look at the pKa of its conjugate acid. The higher the pKa of the conjugate acid, the stronger the base. 12

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15. Resonance… Sterics… 15

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17. Acids, bases, electrophiles, and nucleophiles. For the following molecule, identify which nitrogen atom is more basic. Why? 17

18. Acids, bases, electrophiles, and nucleophiles. For the following molecule, identify the acidic and basic sites and rank them in terms of reactivity (by category; don’t compare acid to base). Rationalize your rankings. 18

19. Acids, bases, electrophiles, and nucleophiles. For the following molecule, identify the acidic, basic, electrophilic, and nucleophilic sites and rank them in terms of reactivity (by category). Rationalize your rankings. 19

20. Acids, bases, electrophiles, and nucleophiles. When solving a mechanism, we can use the different kinds of sites (A, B, E, Nu) to help us. e.g. How can we rationalize the following reaction? 20

21. Acids, bases, electrophiles, and nucleophiles. It is incorrect to mix-and-match the terms acid and electrophile, or base and nucleophile. They are not interchangeable. e.g. I – is a good nucleophile but not a good base It is, however, entirely possible for a molecule to be both an acid and an electrophile – or both a base and a nucleophile. It is even possible for the same molecule to be an acid, a base, a nucleophile and an electrophile all at the same time. In that case, how it reacts will depend on the other species in the reaction flask (since usually the most nucleophilic site reacts with the most electrophilic site – assuming it can reach). 21