Electronic Structure of Oxyallyl Diradical: A Photoelectron Spectroscopic Study

1. 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

2. Trimethylenemethane (TMM)vsOxyallyl TMM diradical Oxyallyl diradical

3. TMM Diradical intermediate in thermal rearrangement of methylenecyclopropane (MCP) TMM diradical intermediate Hydrocarbon Thermal Isomerizations J.J. Gajewski, Academic Press, 1981 JACS1982, 104, 967, Davidson and Borden

4. Trimethylenemethane (TMM) diradical 4 p electrons Triplet Singlet y4 y4 y2 y3 y2 y3 y1 y1 several ways to construct singlet wave functions

5. TMM triplet, singlet wave functions HF energy Triplet wave function 3A2′ (3B2) 2h + J23 – K23 Singlet wave functions 1Ex′ (1B2) 2h + J23 + K23 1Ey′ (1A1) 2h + J22 – K23 1A1′ (1A1) 2h + J22 + K23 where J22− J23 = K23 sizeable exchange interaction triplet ground state (ESR measurements by Dowd, 1960’s)

6. Configuration interaction for 1Ex′ TMM 1Ex′ mixed with Y3→Y4excitation Y1→Y3excitation CI “allyl + p” reduction of electron repulsive interaction at the expense of p bonding energy JACS1976, 98, 2695, Borden

7. Configuration interaction for 1Ey′ TMM 1Ey′ CI with Y3→Y4 and Y1→ Y4 excitation CI “double bond + p + p” reduction of electron repulsive interaction at the expense of p bonding energy

8. Three lowest electronic states of TMM

9. Electron detachment from TMM anion JACS1994, 116, 6961, Wenthold et al. 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 JACS1996, 118, 475, Wenthold et al.

10. Oxyallyl intermediates Thermal stereomutation of cyclopropanone JACS1970, 92, 7488, Greene et al. Photochemistry of quadricyclanone JOC1991, 56, 1907, Ikegami et al.

11. Oxygen substitution: Oxyallyl diradical degeneracy of a2 and 2b1 lifted in oxyallyl JCS,PT21998, 1037, Borden et al.

12. Hartree-Fock for non-degenerate system energy Triplet wave function 3B2 h2 + h3 + J23 – K23 Singlet wave functions 1B2 h2 + h3 + J23 + K23 1A1 h2 + h3 + (J22 + J33)/2 ± [K232 + {h2-h3+(J22-J23)}2]1/2 1A1 The ground state becomes 1A1 if J22− J23 + K23 < h3 – h2

13. Oxyallyl anion : O‾ + acetone reaction “M−H2” ions oxyallyl radical anion carbene radical anion “M−H” ion acetone enolate anion

14. Photoelectron spectrum of M−H ion OH‾ + acetone reaction s radical p radical “M−H” acetone enolate JPC1982, 86, 4873, Ellsion et al.

15. Photoelectron spectrum of M−H2 and M−H ions O‾ + acetone reaction “M−H2” “M−H2” “M−H”

16. Photoelectron spectrum of M−H2 ion “M−H2” detachment from O lone-pair orbitals “M−H2”

17. Photoelectron spectrum of M−H2 ion oxyallyl X1A1 a3B2 EA = 1.945 ± 0.010 eV Te (3B2) = 0.056 ± 0.005 eV

18. Franck-Condon simulation for the 3B2 oxyallyl diradical CCC bending mode 400 ± 20 cm-1 B3LYP/6-311++G(d,p) calculations on 2A2 anion and 3B2 neutral

19. 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.

20. 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