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