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KJM 3600
Hvor pålitelige er de kvantekjemiske metodene ?
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Einar Uggerud
• Metallklynger
• Hydrogeneringsenergier
• Barrierer for SN2-reaksjoner
Oversikt
1) Bottom-to-top approach to
catalytic activity
2) Bridges the gap between
atomic/molecular scale and
solid state/surface.
Metal clusters
Fen+
10
11
12
13
14
15
2.
3.
1.
Fossan, K. O., Uggerud, E.
Dalton Trans. 2004, 892-897.
Produced by laser evaporation of metal with
consequitive condensation in supersonically
expanding He.
Ions transferred to FT-ICR-MS cell.
Reactivity studies
Fe10NH3+
Fe10+
Reactions between Fen+ and NH3
Absolute rate (cm 3 molecule -1 s-1)x10-10
1.0
2.0
3.0
4.0
5.0
Cluster size
Fe4+ + NH3
k= 2.2.10-10 cm3mol-1s-1
-> Fe4NH + + H2
0
-168
-8
-236
-1
B3-LYP/LANL2DZ (kJmol-1)
-121
-97
148
343
B3LYP
149
33
BP86 CASSCF
(8,8)
345 117
Christian Adlhart, upubliserte data
141
174
H2 + C2H4 → C2H6
MP2
301
Eksp.
2H2 + C2H2 → C2H6 311
Reaksjon
Hydrogeneringsentalpier (kJmol-1) for etyn og eten
(298 K, inklusive ZPVE, basis 6-31G(d))
Curtiss, L. A.; Raghavachari, K.; Trucks, G. W.; Pople, J. A.
J. Chem. Phys. 1991, 94, 7221.
1) Innledende geometrioptimialisering: HF/6-31G(d med
tilhørende beregning av nullpunktsvibrasjonsenergien
(ZPVE).
2) Ny geometrioptimialisering: MP2(full)/6-31G(d
3) Deretter en rekke enkeltpunktsberegninger MP2, MP4 og
QCISD(T) i tur og orden med et endelig energiestimat
tilsvarende QCISD(T)/6-311+G(3df,2p) level.
En lagmodell, G2:
Edward Davies Hughes (1906–1963)
SN1
SN2
Christopher Kerk Ingold (1893-1970)
E2
E1
An alcohol
Protonated alcohol
(activated)
+
→ (alkene) + (H2O )2H+
Uggerud, E.; Bache-Andreassen, L.
Chem. Eur. J. 1999, 5, 1917.
Laerdahl, J.K. and E. Uggerud,
Org. Biom. Chem. 2003. 1, 2935.
( R = CH3, CH3CH2, (CH3)2CH and (CH3)3C )
(18OH2 labelled water)
or elimination
H2O + ROH2+
H2O + ROH2+ → ROH2+ + H2O
substitution
Gas phase reactions between water and
protonated alcohols
SN2 Critical step
SN2 transition structures
+
CH3OH2 OH2
CH3OH2 OH2
+
-50.2
+
H2O CH3OH2 +H2OCH3 O H2
-50.2
ts
-46.0
0.0
+
CH3OH2 + H2O
-128.3
-46.0
ts
-7.6
ts
H2O CH3 OH2
+
CH3 +
OH2
OH2
-128.3
0.0
+
CH3OH2 + H2O
MP2 model
Steric hindrance
ts 117.8
Exp.
k , rate
-23.0
-7.6
-5.3
-14.4
4.7
3.3
MP2
MP2//
HF
HF
G2
G3
∆E(kJmol-1)
2.2.10-13
CH3-
Barrier height B3LYP
(cm3molecule-1s-1)
Method
Parameter
-18.6
10.2
8.4
1.3
3.6
-12.3
6.7.10-14
-33.4
-0.7
0.9
-3.3
-2.3
-14.5
4.6.10-11
-52.4
-27.8
-25.7
-20.3
-18.6
-35.1
4.0.10-10
CH3CH2- (CH3)2CH- (CH3)3C-
HF
νTS(cm-1)
i.369
i.428
i.499
MP2
frequency,
i.311
i.363
B3LYP
2.039
HF
Imaginary
2.209
1.953
MP2
i.199
2.060
2.083
1.974
B3LYP
i.117
i.296
i.261
2.622
2.235
2.261
CH3CH2- (CH3)2CH-
r3 (Å)
CH3-
Method
Parameter
i.135
i.166
i.156
2.787
2.689
2.787
(CH3)3C-
Et
1 2 3 4
i-Pr
t-Bu
1,00E-14
1,00E-13
1,00E-12
1,00E-11
1,00E-10
1,00E-09
Results at odds with textbook:
CH3 > CH3CH2 > (CH3)2CH > (CH3)3C
Me
substitution
rate
[cm3molecule -1 s -1 ]
Experiment H218O substitution
∆E
-1
15
10
5
0
-5
-10Me
-15
-20
-25
-30
[kJmol
TS
]
1 2 3 4
Et
i-Pr
Substitution, G3 model
H2O + ROH2+ → ROH2+ + H2O
t-Bu
Me
Et
1 2 3 4
i-Pr
substitution
t-Bu
1,00E-14
1,00E-13
1,00E-12
1,00E-11
1,00E-10
1,00E-09
[cm3molecule -1s-1 ]
rate