2015年度九州大学決断科学大学院プログラム国際シンポジウム … · Sie Thu Minn氏(九州大学大学院生物資源環境科学府) Zar Chi Win氏(九州大学大学院生物資源環境科学府)
AOC No1 5 06 -...
Transcript of AOC No1 5 06 -...
No4 (2016.5.26)
��
���������� ����������������
����������� ����������������
R.G.Pearson,J.Am.Chem.Soc.,1963,85,3533R.G.Pearson,J.Songtad,J.Am.Chem.Soc.,1967, 89, 1827
the small, charged and electronegative fluoride ioncan be seen to be hard, while the large, uncharged andnot strongly electron negative hydrogen sulfide is soft.
F- hardH2S soft
the small, charged proton or the lithium cation can beseen to be hard, while the large silver cation and theuncharged sulfur dioxide are soft.
H+, Li+ hardAg+, SO2 soft
Q: What’s the product?
Q: Which way does the reaction proceed?
3.2 The Principle of Hard and Soft Acids and Bases (HSAB)
“hard-likes-hard and soft-likes-soft”
χ:absoluteelectronegativity
η:hardness
I:ionizationpotential
A:electronaffinity
R.G.Pearson(1968)
H+ I- Ag+ OH- H+ I-Ag+OH-+ +
Hard Acid: small, high positive charge, High-energy LUMOHard Base: small, high negative charge, Low-energy HOMO
Koopman’s theoremIonizationpotential=- HOMOElectronaffinity=- LUMO
“Principle of maximum hardness”
η =9.82– 3.40=6.42=> η =18.7
η =9.82– 3.06=6.76=> η =9.30
R.G.Pearson,Acc.Chem.Res.1993,26,250
Reactions take place in the direction that increase hardness.
R. G. Paar and R. G. Pearson, J. Am. Chem. Soc., 1983, 105, 7512; R. G. Pearson, J. Am. Chem. Soc., 1985, 107, 6801; R. G. Pearson� J. Org. Chem., 1989, 54, 1423; P. K. Chattaraj and P. von R. Schleyer�J. Am. Chem. Soc., 1994, 116, 1067
Scale of Local Hardness
Hard-with-hard, soft-with-soft
(bonddissociation energy)
(acid)
(Base) 3.3 Transition Structure
rate-equilibriumrelationship
reactivityselectivityprinciple?
Thetransitionstructureforanexothermicreactioniscloserinenergytotheenergyofthestartingmaterials,andsoithasmoreofthecharacterofthestartingmaterials (A<B).
Thetransitionstructureforanendothermicreactionisproduct-like(B<A).
Natureoftheproductswillbeinfluential inaffectingtheratesofendothermicreactions(Fig.3.4b),butthatorbitalinteractionswillbeinfluential inexothermicreactions(Fig.3.4a).
Hammond postulate 3.4 Perturbation Theory of Reactivity
ActivationenergySterichindrance
Nostabilizationrepulsion
Frontier orbitals (HOMO, LUMO) interaction is important
2EA >2EB
The Salem-Klopman Equation
1st term:Filled-filledorbitalinteraction(antibondingeffect)à Ignore
2nd term:Coulombic interactionà Importantforcharged/polarmolecules
3rd term:Filled-unfilledorbitalinteractionsà HOMOandLUMO
Example
shouldbehighenergy
Example
3.6 Hard and S0ft Nucleophiles and Electrophile
HSAB=>HSNE
Simplified Klopman-Salem Equation
ΔE = - QnucQelec + 2(cnuccelec β)2
ε R EHOMO - ELUMO
2nd term 3rd term
HARD nucleophile/HARD electrophile
SOFT nucleophile/SOFT electrophile
NUMERATOR DENOMINATOR
2nd TERM 3rd TERM
STEPWISE CONCERTED
4 Ionic Reactions − Reactivity
Curved Arrows show the flow of electrons
Addition
Why would a pair of electrons act together to move from one bond into another?
SN2
AN
AE
4.1 Single Electron Transfer (SET) in Ionic Reactions
R.A.Rossi,Chem.Rev.2003,103,71Charge-Transfer Complex
slow
fast
SRN1 reaction (Radical Nucleophilic Substitution) Nucleophilic and electrophilic attack on a double bond via CT complex
4.2 Nucleophilicity
4.2.1 Heteroatom Nucleophiles
kNu: rate constant (or equilibrium constant) for a reaction K0: rate constant (or equilibrium constant) for water as the nucleophile EN: rate of the reaction with methyl bromide H: (pKa + 1.74) ( = pKa of H3O+)
softnesshardness
J.O.Edwards,JACS 1954,76,1540 (Scale of nucleophilicity)
α/β ~large=> Soft electrophile
Softness and Hardness of Inorganic Nucleophiles and Electrophiles
G.Klopman,JACS1968,90,���
Solvationcorrection
(i)ELUMO =-7eV (HS- >I- >CN- >Br->Cl->HO- >F- )
(ii)ELUMO =-5eV (HS->CN- >I- >HO->Br->Cl->F- )
(iii)ELUMO =+1eV (HO->CN- >HS->F- >Cl- >Br-> I- )
G.Klopman JACS 1968,90,2234.2.2 Solvent Effects
SN2 Reaction in the Gas Phase
J.Mikosch,Science 2008,319,183
J.I.Brauman,Science 2008,319,168
Solvent changes the reaction pathways
HOMOsolvent/LUMOreagent andLUMOsolvent/HOMOreagent Using the concept of HSAB theory, predict which way, LEFT or RIGHT, that the following reactions will tend to proceed:
a. CaS + H2O ↔ CaO + H2S
b. AlI3 + 3NaF ↔ AlF3 + 3NaI
c. Mg(OH)2 + Cu(SCN)2 ↔ Mg(SCN)2 + Cu(OH)2the S end of SCN is coordinated
d. CdI2(s) + CaF2(s) ↔ CdF2(s) + CaI2(s)
e. [CuI4]2–(aq) + [CuCl4]3–(aq) ↔ [CuCl4]2–(aq) + [CuI4]3–(aq)
f. NH2–(aq) + H2O(l) ↔ NH3(aq) + OH–(aq)
g. 2 LiI + CoCl2 ↔ 2 LiCl + CoI2
Report No4 (5/27)