Anions 2007Azolide Ion Chemistry
Park City, UTJuly, 2007
Takatoshi Ichino, Shuji Kato, Stephanie VillanoJohn Stanton and Veronica M. Bierbaum
Carl LinebergerJILA and Department of Chemistry
University of Colorado
Happy 59th, Ken!!&
Thanks for everything, Jack!
Outline and Rationale• Theory ⇐⇒ experiment, synthesis,• Selected ion flow tube (SIFT) and flowing afterglow
– Gas phase synthesis of nitrogen-rich ions– Characterization of stability and structure
• Reaction chemistry: acidity, collisional dissociation, structure
• Anion photoelectron spectroscopy– Electron binding energies, ground state surface properties– Low-lying excited states, structure, bond strengths– Simulations of spectra using calculated structures– Most B3LYP/6-311++G(d,p)– Most useful with small geometry changes– Can be problematic with moderate ones: CH2
-, SF6-, . . .
– Useful with very large changes: isomers, conformers, clusters– Vibronic coupling raises complex issues (ignored here today)
Azolides and related anions
-
Pyrazole (vibronic coupling)N-methyl pyrazole (deprotonation site ID)N-methyl imidazole (selective reactions)Vinyl diazomethyl anion (conformational selectivity)1H -1,2,3 triazole (everything happens)
C5-nH5-nNn-
Azolides formed by OH- deprotonation of azoles at known T
Negative Ion Photoelectron Spectrometer
B
E x BMass Filter
I(KE)e-
He
m wave
Roots Pump
uv laser351 nm
Reagents
LN2 jacket
A-R-
hν + A- → A + e- (KE)
10 20 30 40 50 60 70 80 90 1000
500
1000
1500
2000
2500
0m/z
N
m/z 66
0
400
800
1200
1600
10 20 30 40 50 60 70 80 90 1000m/z
-
NN
m/z 67
Generation of M-1 Anions Via OH- Deprotonation
Note m/e = 40 second product
Other reactions appear to haveonly one ionic product.10 20 30 40 50 60 70 80 90 100
0
1000
2000
3000
4000
0m/z
NN
N
m/z 68
Negative Ion Photoelectron Spectroscopy
AB– + hν AB +e–
hν
EA(AB)VDE(AB–)
AB–
AB
←Electron binding energy
Intensities governed by Franck-Condon factorsInstrument resolution is 5 meV (40 cm-1 or 0.1kcal/mol)ΔS= ± 1 selection ruleUse DFT calculations and full FCF simulation to compare with exp.
O2- and O2 Electronic Potentials
R, Angstrom
Ener
gy, c
m-1
How well can one fit the observed photoelectron spectrumby optimizing O2
- properties: re, ωe, S-O, and EA?
1.0 2.0 3.0
0
20,000
40,000
O2- 2Π1//2, 3/2
O21Σ
O21Δ
O23Σ
O2- photoelectron spectrum simulation
K. Ervin, I. Anusiewicz, P. Skurski, J. Simons and WCL,J. Phys Chem. A 107, 8521 (2003)
EA=1.161 eV
Phot
oele
ctro
n C
ount
s
0
1 0 0
2 0 0 R o t a t io n a l /S p in - O r b i tC o n t o u r
EA=1.161 eV
0 . 51 . 01 .52 .02 . 53 . 00
1 0 0
2 0 0
electron binding energy, eV
3Σ 0−01Δ 0−0
1Σ 0−0
EA(O2)
Fit
Experiment
C4 C3
N2N1
C5
H H
C4 C3
N2N1
C5
H
H
C4 C3
N2N1
C5
H
H
C4 C3
N2N1
C5
H
C4 C3
N2N1
C5
H
H
+ HO + H2O
H
HH
+ H2OH
H
H+ H2O
H
+ H2O
ΔrxnHo
- 35.4 kcal mol-1
(exp -36.7 ± 0.4)
- 5.8 kcal mol-1
+ 9.9 kcal mol-1
+ 6.6 kcal mol-1
pyrazole 1-pyrazolide
3-pyrazolide
4-pyrazolide
5-pyrazolide
Pyrazole reactions with hydroxide
-5.8 kcal mol-1
All are m/e =66
-6 kcal/mol
-35 kcal/mol
Electron Binding Energy (eV)
2.02.22.42.62.83.03.2
C5C4 C3
N2N1H
H
H
H
pyrazolide anions photoelectron spectrum
5-pyrazolyl
1-pyrazolyl
Test assignments by “blocking” N1 site with CH3.
N-methyl-pyrazole reactions with OH-
C
C C
NNCH3
H
5C
4C C3
N2N1CH3
H
H
C
C C
NNCH2
H
H
C
C C
NNCH3
H
C
C C
NNCH3
H
+ HO
ΔrxnH0
+ H2O
+ H2O
+ H2O
+ H2O
H
H
H
H
H
-5.0 kcal mol-1
+1.4 kcal mol-1
+7.9 kcal mol-1
+11.3 kcal mol-1
All are m/e =71
Electron Binding Energy (eV)
1.82.02.22.42.62.83.03.23.4
C
C C
NNCH3
H H
Electron Binding Energy (eV)
electron binding energy, (eV)
1.82.02.22.42.62.83.03.23.4
2A"
2A'Ab initio simulation
N-methyl-5 -pyrazolide photoelectron spectrum
Simulation is convincing confirmation of C5 deprotonation.
Electron Binding Energy (eV)
1.82.02.22.42.62.83.03.23.4
C
C C
NNCH3
H H
Electron Binding Energy (eV)
electron binding energy, (eV)
1.82.02.22.42.62.83.03.23.4
2A"
2A'Ab initio simulation
N-methyl-5 -pyrazolide photoelectron spectrum
What will happen when more reaction channels are open?
N-methyl-imidazole reactions with OH-
C
C N
CNCH3
H
H
5C
4C N3
C2N1CH3
H
H
H
C
C N
CNCH2
H
H
H
C
C N
CNCH3
H
H
C
C N
CNCH3
HH
+ HO
ΔrxnH0
+ H2O
+ H2O
+ H2O
+ H2O
-2.5 kcal mol-1
-1.7 kcal mol-1
-0.9 kcal mol-1
+15.5 kcal mol-1
C
C N
CNCH3
H
H
C
C N
CNCH3
H
H
All are m/e =71
N-methyl imidazolide pe spectrum
Electron Binding Energy, (eV)1.21.62.02.42.83.2
Phot
oelect
ron
Coun
ts
2.02.12.2
a
b
cd
e
a
y
x
How well does the simulation reproduce the detailed structure?
N-methyl imidazolide expanded view of simulation & experiment
Electron Binding Energy, (eV)
1.952.002.052.102.152.202.25
Phot
oele
ctro
n C
ount
s
C
C N
CNCH3
H
H
C
C N
CNCH3
H
H
C
C N
CNCH3
H
H
But which anion structure(s) are present?
electron binding energy, eV
0.51.01.52.02.53.0
N-methyl imidazolide pes simulations
C
C N
CNCH2
H
H
H
C
C N
CNCH3
H
H
C
C N
CNCH3
H
H
C
C N
CNCH3
H
H
C
C N
CNCH3
H
H
data
simulation
simulation
simulation
electron binding energy, eV
0.51.01.52.02.53.0
N-methyl imidazolide pes simulations
C
C N
CNCH2
H
H
H
C
C N
CNCH3
H
H
C
C N
CNCH3
H
H
C
C N
CNCH3
H
H
C
C N
CNCH3
H
H
data
simulation
simulation
simulation
Only the C5 deprotonation product is present in significantyield, although all three isomers are energetically accessibleWhat is the “blob” at lower eBE? Same mass. Ring open?
Vinyldiazomethyl (vdm) anion chemistry
N NC
CC
H
HH
CN
H2CCN
H2CCCH
H3CCN
HCN
N2
_
collisionalactivation
path a
path b
+_
+_
+path c
_
H2CCHCNNpath d
_
+26 kcal mol-1
+31 kcal mol-1
+4.4 kcal mol-1
+40 kcal mol-1
C
C
H H
H C
NN
_H2O+
CCC
H H
H H
H
N2O+_
CC
H H
H CNN
_H2O+
Produce the ring open form in reaction of allyl anion with N2O.
Both E- and Z- conformations of vdm- may be present
Vinyldiazomethyl anion pes
Electron Binding Energy (eV)1.82.02.22.42.62.83.03.2
Phot
oele
ctro
n Co
unts
A 2A'
X 2A"CC
H H
H CNN
_
Can simulations differentiate between E- and Z- conformers?
Vinyldiazomethyl anion chemistry
Electron Binding Energy (eV)1.81.92.02.12.2
Z-vinyldiazomethyl
CC C
NN
H
H
H
_
E-vinyldiazomethyl
CC
H H
H CNN
_
Yes!
So we will use this capability to look at a complex reaction.
1H-1,2,3 triazole reaction with OH-
OH- + C2N3H3 → (m/e 68)- + H2O major product→ (m/e 40)- + neutral(s) smaller
NN
NH
H
H
Gentle CID on m/e 68 gives extensive m/e = 40 anion(s)
What are the identities, structures and energeticsof these anions?
Can we infer plausible reaction mechanisms?
1,2,3,triazolide imaging pe spectrum
electron binding energy (eV)3.403.453.503.553.603.653.70
Phot
oelect
ron
coun
tsN
NN
H H
-actuallym/e = 68
355, 335, 320 nm images
electron binding energy, eV3.33.43.53.63.73.8
phot
oelect
ron
coun
ts
NN
N
H H
-
m/e = 68
But there is photoelectron signal at lower binding energies.
electron binding energy, eV
1.82.02.22.42.62.83.03.2
Phot
oelect
ron
Coun
tsm/e = 68 photoelectron spectrum
x 10
And there is the other m/e = 40 reaction product:
Electron Binding Energy (eV)
1.41.61.82.02.22.42.62.83.03.2
Phot
oelect
ron
Coun
ts
m/e = 40 photoelectron spectrum
So how do we rationalize all these data?
Triazole N1 deprotonation by OH-
0
−62.3
−47.2
HO_
+NN
NH
H
H
C NN
NCH
H
_
H2O C CN
NN
H H
_H2O+
m/e=68
electron binding energy (eV)3.403.453.503.553.603.653.70
Phot
oelect
ron
coun
ts
1,2,3,triazolide imaging pe spectrum
NN
N
H H
-
EA = 3.447(4) eV
What are the identities, structures andformation mechanisms for the minor reaction products?
Indirect C4 deprotonation within complex
HO_
+NN
NH
H
H
C NN
NCH
H
_
H2O
C NN
NCH
H
_ H2O
C CN
NN
H H
_H2O+
−47.2
m/e=68
0
−62.3 −62.2
HO_
+NN
NH
H
H
NN
NH H
HOH
_
−4.2
−22.7
−3.2
m/e=68
NN
N
_H2O+
H H
C4 deprotonated product observed
E le c t r o n B in d in g E n e rg y (e V )
1 .82 .02 .22 .4
Phot
oelect
ron
Coun
ts
NN
N
_
H Hsimulation
m/e =68 data
0
−17.0
+0.1
−27.4
−2.5
+3.0
−14.9
−19.0
−31.7
HO_
+NN
NH
H
H
NN
NH
H
HOH
_
NN
NH
H
HOH
_NC
H
H CNN
H2O_NC
H CNN
H2O_
H
NC
H CNN
_H2O+
H
NC
H
H CNN
_H2O+
NN
NH
_H2O+
H
NC
H CNN
H2O_
H
C4 attack by OH-leads to ring opening
70 %
30 %
−3.2
m/e=68
Electron Binding Energy (eV)
2.42.52.62.72.8
Both conformers are present
NC
H
H CNN
_
NC
H CNN
_
H
m/e = 68 data
Simulation
Simulation
0.7 A + 0.3 B
0
−33.4
−17.2 −15.5
−32.4
−60.4
HO_
+NN
NH
H
H
NN
N
H
H
HOH _
NN
N
H
H_HOH
NN
N
H
H
_H2O+
N C CH
H
H2ON2
_
++
C C NH
H
H2O
_
++
N2
m/e=68
m/e=40
m/e= 40?
ketenimine
C5 attack also leads to ring opening
electron binding energy, eV1.41.61.82.02.22.4
Phot
oelect
ron
Coun
ts
Improved m/e = 40 data
Very likely two species in spectrum. Try to model them.
Phot
oelect
ron
Coun
ts
E lectron Binding Energy (eV)
1.41.61.82.02.22.4
C C NH
H
_
data
authentic
subtractedN C C
H
H _
Both m/e = 40 products are present
X 2A”
In Conclusion . . .The combination of flowing afterglow ion chemistry
and anion photoelectron spectroscopy can provide unique data on the structure, energetics and reactions of highly unstable species.
HAPPY BIRTHDAY, KEN!!!!
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