pKas – Chemistry

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Hydrobromic Acid
answer

HBr
-9
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Hydrochloric Acid
answer

HCl
-8
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Picric Acid
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(NO2)3C6H2OH
0
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Hydrofluoric Acid
answer

HF
3.2
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Acetic Acid
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HCO2CH3
4.75
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Benzoic Acid
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PhCo2H
4.25
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Hydrazoic Acid
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HN3
4.7
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Cyanic Acid
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HCN
9.1
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Thiophenol
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PhSH
6.5
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Ammonium
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NH4+
9.2
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Phenol
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PhOH
10.0
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trifluoroethanol
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F3CCh2OH
12.4
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Amide
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Ch3CoNH2
15.1
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methanol
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15.5
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water
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H20
15.75
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Alkane Chain Length
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Decreases acidity in solution (makes it harder to solvate)
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Electrowithdrawing group
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Increase Acidity by stabilizing the anion
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Ketones
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20
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thiols
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about 10
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esters, nitriles, sulfones
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~25
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Alcohols
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16-18
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Adenine
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[image]
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Thymine
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[image]
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Guanine
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[image]
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Cytosine
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[image]
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Uracil
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[image]
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Toluene
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C6H5CH3
37
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ethers
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~20
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E vs. Z acids
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Acids prefer the Z-form by about 5 kcal/mol
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Carbocation Stability
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More substituted carbons more stable cation because of electron donating methyls and hyperconjugation/resonance
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Carbanions
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Stability affected by Electronegativity, delocatiolization of charge
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Activation Energy -> half life
3 5 10 15 20 30
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3->17E-12s
5->4.8E-10s
10->2E-6s
15->0.0084s
20->35s
30->6916 days
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Radicals
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More substituted carbons also more stable radicals
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Equilibrium Constants and Free Energy Difference
0
-1.36
-2.72
-4.08
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0 -> K = 1 50% each
-1.36 -> K = 10 90% 10%
-2.72 -> K = 100 99% 1%
-4.08 -> K = 1000 99.9% 0.1%
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Thorpe-Ingold Effect
Gem-dimethyl Effect
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Increasing size of substituents of tetrahedral center increases reaction rate between other two and decreases the angle
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Anomeric Effect
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Explains why OCH3 prefers axial when in a heterocycle, and why hydrogen peroxide is at 120
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Inductive Effect
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Withdrawing Electrons through sigma bonds to the more electronegative group
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Field Effect
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polarization through charges that interact through space
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Hybridization Formula
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cos @ = -1/m
sp^m
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Electronegativity
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1/2(Ionization Potential + Electron Affinity)
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Hill Plot
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log ([SL]/[S]) vs. log [L]

expect 1 but if slope greater than one hints at cooperativity

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Benensi-Hildebrand Plot
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Double Reciprocal
1/[Fraction of S] vs. 1/[L]
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Scatchard Plot
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calculates affinity constant of ligand with protein
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R lnKa =
(with heat capacity)
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-dH/T + CplnT + (dS-dCp)
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dielectric constant
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Measured by the shielding a solvent gives when put between a capacitor by opposing the E-field
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Kirkwood Factor
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Related to the Bell Equation and Dielectric Constant

e-1/2e+1

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delta-d
Solubility
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Hildebrand

“Cohesive Energy Density”

d^2 = dH(vap) – RT/molar volume

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Kosover Z-Scale (Z)
Reichardt Scale (Et)
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From Absorption Spectra of salts

The more polar the solvent the higher the frequency of light needed to go from ion pair to two radicals

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Y Scale
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Winstein and Grunwald
Used rates of solvolysis of t-Bu chloride
log ky/k0 = mY

m – substrate specificity
Y = solvent scale and also related to Et
k0 based off 80% aquaous ethanol (20% water)

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Why Water is weird
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1) Temperature of max density higher than melting point
2)thermal expansion 1/V(dV/dT) is negative from -20 to 4
3) Bulk Modulus Kappa= -VdP/dV
has minimum at 46 C
4)Cp pretty much constant from 0-100 but changes a lot at low temperatures
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18-crown-6
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K+
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15-crown-5
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Na+
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Crown Ethers and Macrocycles pioneered by:
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Cram, Lehn, Petersen
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spherands
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[image]
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Rebek
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Kemp’s Triacid to bind DNA bases
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Hamilton
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Cyclophane like things to make bind adenine
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Zimmerman
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Molecular Tweezers
3 aromatic portions with acid moeity to bind
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Secondary vs. Primary H-bonding
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Primary worth 7.5
Secondary worth 2.5
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Cyclophanes
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Diederich
evolved from Pedersens crown ethers
Had solubilizing Ammonium Groups
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alpha-effect
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larger anions not as well solvated, originally thought to be lone-pair lone-pair repulsions
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Hammett Equation
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log Kx/Ko = sigmax * rho
a positive sigma -> electron withdrawing
negative -> electron donating
?>1, the reaction is more sensitive to substituents than benzoic acid and negative charge is built during the reaction.
0<?<1 , the reaction is less sensitive to substituents than benzoic acid and negative charge is built.
?=0, no sensitivity to substituents, and no charge is built.
?<0, the reaction builds positive charge.
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Swain-Scott Equation
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log (k/ko) = sn
n = nucleophilicity
s = substrate specificity
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Grunwald-Winstein Equation
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log(k/ko) = mY

Y is solvent scale
m is sensitivity of substrate

based of solvolysis of t-butyl chloride in 80% aqueous ethanol

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alpha-carbonyl effect on Sn2
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has to be in the same plane with p orbital of carbonyl and siqma star LUMO

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