J. M. Ready
UT Southwestern
Valuable Numbers
pKa's. Numbers are approximations for outside the range -2 - 16, but useful to know.
For an extensive list, see http://www.chem.wisc.edu/areas/reich/pkatable/
H2O DMSO
H2O DMSO
Substrate
Substrate
Inorganics
CF3SO3H
-14
HCl
CH3SO3H
-8
H3O+
-2
NH4Cl
9
O
O
O
O
9
13
11
14
13
EtO
OEt
10
NO2-CH3
16
EtO
16
Organic X-H
H +
O
Ph
O
2
-3
H2O
EWG-CH
O
O
-6
CH3
20
27
25
30
O
Me2OH+
AcOH
NH+
PhOH
O
N
H
17
H
-4
5
12
5
3
10
18
15
26
t-BuO
O
Me2N
35
O
S
33
Hydrocarbons
H
MeOH
16
28
tBuOH
17
29
(iPr)2NH
38
R
H
98
H
103
H
125
H
H
H H
Bond Strength. Take from Lowry and Richardson; by definition, ΔH for:
Bond
44
H
41
BDE (Kcal/mol)
50
H3C
36
NH3
35
Bond
23
35
A +
A B
BDE (Kcal/mol)
OH
84
O
172 (2nd bond = 88)
B
85
81
Cl
82
Br
69
I
54
HO H
HO2 H
119
90
HO OH
50
104
2-10
H H
Hydrogen bond X H
148 (2nd bond = 67)
194 (3rd bond = 46)
for a large list of BDE's see Prof. Thomas Lectka's web page:
http://www.jhu.edu/chem/lectka/Bond%20Strengths.html
Strain energy (energetic penalty for indicated strain)
H3C
Strain
CH3
H
Penalty (kcal/mol)
ring strain
0.8
gauche
H
H
H
H3C CH3
eclipsed
CH3
CH3
or
O
or
O
28
26
2.2
H
H
H
H
Penalty (kcal/mol)
Strain
6
syn-pentane
3.7
0
olefin conformations
H3 C
CH3
for
CH3
H
H3 C
H3C
H
CH3
6
A1,2
2.7
H
H3C
H
CH3CH3
A1,3
3.9
Kinetics and Thermodynamics
equilibrium processes
key equation: ∆G = -RTLn(K)
for K = 10, T = 298, ∆G = -1.4kcal
K = 100, T = 298 ∆G = -2.8kcal
i.e. for every 1.4kcal difference in energy there
is an order of magnitude change in Keq
reaction rate
2nd key equation
kBT
−∆G‡
exp
k=
h
RT
or
∆G‡ = -RTLn
kh
kBT
for T = 298, k = 1s-1
∆G‡ = 17.5 kcal/mol
i.e. activation energy for rxn occuring once a second is 17.5
As above, if k = 10s-1, ∆G‡ = 17.5 - 1.4 = 16.1
k = rate constant
h = Plank's constant
kb = Boltzmann's constant
−∆G‡ = free energy difference between
ground state and transition state
For T = 308 and ∆G‡ = 17.5, k = 2.5s-1
i.e. increase in temp of 10K gives ~2.5 fold increase in rate
relative rates
for a system with 2 possible reaction pathways (e.g. kinetic enolization or asymmetric catalysis) for
kfast/kslow = 10 (would give 82% ee), ∆∆G‡ = 1.4kcal/mol
kfast/kslow = 100 (would give 99% ee), ∆∆G‡ = 2.8kcal/mol
Bond distances
length (angstroms [10-10m])
bond
OH
1.43
O
1.23
1.53
1.34
1.20
H
1.1
H3 C
H
H3 C O
X
H
(hydrogen bond)
0.97
1.5 - 2.4