1. Ch. 3 – Organic Transformations, Acidity & Basicity
HW pbs
7,9,14,16,26,27,28,29,31,32,33

2. pKa p = - log thus, pH = - log (H3O+) and, pKa = - log Ka Ex.
acid Ka pKa acid strength
A x weakest acid
B x
C x strongest acid

3. Ex. Which would phenoxide deprotonate (undergo an
acid/base reaction with), a ketone or a carboxylic acid?
compound pKa
acetone ~ 20
carboxylic acid ~ 5
phenol ~ 9
Answer: a carboxylic acid  think of the conjugate bases
competing for the proton

6. At equilibrium, DGrx = -2.3 RT log Keq
smaller DG corresponds to larger K
anything that dec value of DG will shift eq to the right: inc R energy (destabilize R), lower P energy (stabilize P), or both
anything that inc value of DG will shift eq to the left: dec R energy (stabilize R), raise P energy (destabilize P), or both

7. typically, anion, cation, and radical species are less stable and higher in energy than their neutral, even electron counterparts
typically in our comparison of acid/base reactions, if the energy of the products differ, then we will assume the energy difference between reactants to be negligible. Similarly, if the energy of the reactants differ, then we will assume the energy difference between products to be negligible

8. Ex. Consider: XH  X H+
YH  Y H+
Assume XH is a stronger acid than YH. This may be due to X- being
more stable than Y- , or, due to YH more stable than XH. Either way,
the XH rx has a lower DG value, (larger K), than the YH rx. DG=GP-GR

9. Some factors determining acidity/basicity:
1) Hybridization effects
because s orbitals are lower in energy than p orbitals, es become increasingly stabilized when they reside in hybrid orbitals with increasing amounts of s character
inc in acid strength as s char inc due to inc stabilization of conjugate base

10. Ex. Consider acidity of terminal alkynes, terminal
alkenes, and alkanes
pKa 50 44 25

11. AH is the weakest acid and CH is the strongest acid due
to the greatest stabilization of C- and lowest stabilization
of A- . CH rx has the lowest DG value and AH reaction
has the highest DG value .

12. 2) Inductive effects
primary effect is increasing stabilization of conj base as highly electronegative atoms disperse negative charge
inductive effect is a through bond effect that falls off quickly with the # of intervening bonds, i.e. is not a through space effect

13. Ex.
most acidic least acidic
most acidic least acidic

14. Ex. Which one of the following two bases are stronger?
B- is a stronger base than A- due to the stabilization of A-
wrt B- . B rx has a smaller DG value than A rx.

15. 3) Resonance effects
recall: resonance is a stabilizing effect
Ex. BH is a stronger acid than AH due to the stabilization
of B- wrt A- . B rx has a smaller DG value than A rx.

16. Acidity / Basicity of Organic Functional Groups:
acidic: RCOOH (carboxylic acids) pka ~ 5
Ph-OH (phenols) pka ~ 9
basic: RNH2 (amines) pka ~ 35
(1, 2, 3)
other organic functional groups leave pH unchanged when added to water