electronic structure of oxyallyl diradical: a photoelectron spectroscopic study takatoshi ichino,...
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Electronic Structure of Oxyallyl Diradical:A Photoelectron Spectroscopic Study
Takatoshi Ichino, Rebecca L. Hoenigman, Adam J. Gianola,
Django H. Andrews, and W. Carl Lineberger
JILA and Department of Chemistry and Biochemistry,
University of Colorado, Boulder, CO 80309
Weston T. Borden
Department of Chemistry, University of North Texas
Denton, TX 76203
Stephen J. Blanksby
Department of Chemistry, University of Wollongong
Wollongong, NSW 2522, Australia
Trimethylenemethane (TMM)vs
Oxyallyl
C
CCC
H
H
H
H
O
CCC
H
H
H
H
HH
TMM diradical Oxyallyl diradical
TMM Diradical intermediate in thermal rearrangement of methylenecyclopropane (MCP)
X X
TMM diradicalintermediate
Hydrocarbon Thermal IsomerizationsJ.J. Gajewski, Academic Press, 1981
JACS 1982, 104, 967, Davidson and Borden
Trimethylenemethane (TMM) diradical
CH2
CH2C CH2
1: 1a2" (1b1)
2: ex" (a2) 3: ey" (2b1)
4: 2a2" (3b1)
4 electrons
Triplet Singlet
several ways to constructsinglet wave functions
1
2 3
4
1
2 3
4
TMM triplet, singlet wave functions
22332
22332
23322
23322
Triplet wave function 3A2′ (3B2)
Singlet wave functions 1Ex′ (1B2)
1Ey′ (1A1)
1A1′ (1A1)
HF energy
2h + J23 – K23
2h + J23 + K23
2h + J22 – K23
2h + J22 + K23
where J22 − J23 = K23
sizeable exchange interaction
triplet ground state (ESR measurements by Dowd, 1960’s)
Configuration interaction for 1Ex′ TMM
223113211
224114211
223313213
1Ex′
mixed with
1
2 3
1
2 3CI
“allyl + p”
reduction of electron repulsive interactionat the expense of bonding energy
3 → 4 excitation
1 → 3 excitation
JACS 1976, 98, 2695, Borden
Configuration interaction for 1Ey′ TMM
22
2
323211323211
33112211
1Ey′
CI with 3 → 4 and 1 → 4 excitation
1
2 3
1
2+3)/21/2 2 3)/21/2
CI
“double bond + p + p”
reduction of electron repulsive interactionat the expense of bonding energy
Three lowest electronic states of TMM
C
C
HH
CCH
H
H
H
C
C
HH
CCH
H
H
H
C
C
HH
CCH
H
H
H
C
CCC
H
H
H
H
HH
3A2' (3B2) 1B21A1
1B1
Electron detachment from TMM anion
CH2
CH2C CH2
SiMe3SiMe3
F- CH2
C
Me3Si
CH2H2C
F2 CH2
CH2C CH2- FSiMe3
- FSiMe3
- F
EA (TMM) = 0.431 ± 0.006 eV
E (X 3A2′ ― b 1A1) = 0.699 ± 0.006 eV
CCC bend in 3A2′ : 425 ± 20 cm-1
in 1A1 : 325 ± 20 cm-1
JACS 1996, 118, 475, Wenthold et al.
JACS 1994, 116, 6961, Wenthold et al.
Oxyallyl intermediates
O
t-Bu HH t-Bu
O
t-Bu
H
H
t-Bu
O
H t-But-Bu H
O O
h
Thermal stereomutation of cyclopropanone
Photochemistry of quadricyclanone
JACS 1970, 92, 7488, Greene et al.
JOC 1991, 56, 1907, Ikegami et al.
Oxygen substitution: Oxyallyl diradical
JCS,PT2 1998, 1037, Borden et al.
degeneracy of a2 and 2b1 lifted in oxyallyl
Hartree-Fock for non-degenerate system
22332
22332
23322
23322
Triplet wave function 3B2
Singlet wave functions 1B2
1A1
1A1
energy
h2 + h3 + J23 – K23
The ground state becomes 1A1 if J22 − J23 + K23 < h3 – h2
h2 + h3 + J23 + K23
h2 + h3 + (J22 + J33)/2± [K23
2 + {h2-h3+(J22-J23)}2]1/2
Oxyallyl anion : O‾ + acetone reaction
O C
O
H3C CH3C
O
CH2H2C
C
O
CH3HC
C
O
CH3H2C
- H2O
- H2O
+
- OH
“M−H2” ions
“M−H” ion
oxyallylradical anion
carbeneradical anion
acetoneenolate anion
Photoelectron spectrum of M−H ion
electron binding energy (eV)
1.52.02.53.0
Pho
toel
ectr
on c
ount
s
0
200
400
600
800
1000
1200
C
O
CH3H2C
radical radical
OH‾ + acetone reaction
“M−H”
acetone enolate
JPC 1982, 86, 4873, Ellsion et al.
Photoelectron spectrum of M−H2 and M−H ions
electron binding energy (eV)
1.52.02.53.0
Pho
toel
ectr
on c
ount
s
0
200
400
600
800
1000 C
O
CH2H2C
C
O
CH3HC
C
O
CH3H2C
O‾ + acetone reaction
“M−H2”
“M−H2”
“M−H”
Photoelectron spectrum of M−H2 ion
electron binding energy (eV)
1.52.02.53.0
phot
oele
ctro
n co
unts
0
200
400
600
800
1000
C
O
CH2H2C
C
O
CH3HC
“M−H2”
“M−H2”
detachment fromO lone-pair orbitals
Photoelectron spectrum of M−H2 ion
electron binding energy (eV)
1.61.82.02.22.4
phot
oele
ctro
n co
unts
0
200
400
600
800
1000
1200
magic angle0 degree90 degree
X 1A1a 3B2
EA = 1.945 ± 0.010 eV Te (3B2) = 0.056 ± 0.005 eV
O
CCC
H
H
H
H
O
CCC
H
H
H
H
3B2
1A1
oxyallyl
electron binding energy (eV)
1.61.82.02.22.4
phot
oele
ctro
n co
unts
0
50
100
150
200
250
300
350
experiment (0 degree)Franck-Condon simulation
Franck-Condon simulation for the 3B2 oxyallyl diradical
B3LYP/6-311++G(d,p) calculations on 2A2 anion and 3B2 neutral
CCC bending mode400 ± 20 cm-1
Conclusions
• The 351 nm photoelectron spectrum of oxyallyl anion has been measured. The Franck-Condon fitting is successful for the transition from the 2A2 ground state of oxyallyl anion to the 3B2 state of oxyallyl, based on B3LYP/6-311++G(d,p) optimized geometries and normal modes. Vibrational progression is observed for a CCC bending mode of 400 ± 20 cm-1 in the 3B2 spectrum.
• Angular distributions of the photoelectrons from oxyallyl anion reveal an electronic state of oxyallyl to the lower electron binding energy side of the 3B2 spectrum. This is assigned to the 1A1 ground state of oxyallyl. The electron affinity of oxyallyl is 1.945 ± 0.010 eV, and the term energy for the 3B2 state is 0.056 ± 0.005 eV.
Acknowledgements
• Adam J. Gianola, Django H. Andrews, Rebecca L. Hoenigman, and
W. Carl Lineberger, University of Colorado at Boulder
• Stephen J. Blanksby, University of Wollongong, Australia
• Weston T. Borden, University of North Texas
• NSF, AFOSR