Electronic Structure of Oxyallyl Diradical: A Photoelectron ...

Electronic Structure of Oxyallyl Diradical: A Photoelectron ...

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 TMM diradical H H C H C C Oxyallyl diradical H C H O H H C H C C

H H TMM Diradical intermediate in thermal rearrangement of methylenecyclopropane (MCP) X X TMM diradical intermediate Hydrocarbon Thermal Isomerizations J.J. Gajewski, Academic Press, 1981 JACS 1982, 104, 967, Davidson and Borden Trimethylenemethane (TMM) diradical CH2 H2C C 4 electrons CH2 Triplet Singlet 4 4 4: 2a2" (3b1) 2 3: ey" (2b1) 2: ex" (a2) 1: 1a2" (1b1) 3

1 2 3 1 several ways to construct singlet wave functions TMM triplet, singlet wave functions HF energy A2 (3B2) 32 2 2h + J23 K23 Ex (1B2) 32 2 2h + J23 + K23 Ey (1A1) 33 2

2h + J22 K23 A1 (1A1) Triplet wave function 3 Singlet wave functions 1 1 1 2 2 2 2 3 3 2 2 33 2 2h + J22 + K23 where J22 J23 = K23 sizeable exchange interaction triplet ground state (ESR measurements by Dowd, 1960s)

Configuration interaction for 1Ex TMM 1 Ex 1 1 2 3 1132 mixed with 2 2 1 1 2 4 114 2 3 1 2 3 1332

3 CI 1 2 3 4 excitation 2 1 3 excitation 2 3 1 allyl + p reduction of electron repulsive interaction at the expense of bonding energy JACS 1976, 98, 2695, Borden Configuration interaction for 1Ey TMM 1 Ey 2 1 1 1 2 1 2

1 2 3 1 2 3 3 3 1 1 2 3 2 3 2 2 CI with 3 4 and 1 4 excitation 2+3)/21/2 2 2 3)/21/2 3 CI 1 1 double bond + p + p reduction of electron repulsive interaction

at the expense of bonding energy Three lowest electronic states of TMM 3 A2' (3B2) H 1 H C H C C H C B2 H H H 1 H C C C H H C H

H HH C H C H C C H H H C H 1 B1 A1 H C C H C H H Electron detachment from TMM anion CH2 H2C C

F CH2 SiMe3 SiMe3 - - FSiMe3 Me3Si H2C CH2 C CH2 F2 CH2 -F H2C C CH2 - FSiMe3 JACS 1994, 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 JACS 1996, 118, 475, Wenthold et al. Oxyallyl intermediates Thermal stereomutation of cyclopropanone O O

O t-Bu t-Bu H H t-Bu H H H t-Bu t-Bu t-Bu H JACS 1970, 92, 7488, Greene et al. Photochemistry of quadricyclanone O O h JOC 1991, 56, 1907, Ikegami et al. Oxygen substitution: Oxyallyl diradical degeneracy of a2 and 2b1 lifted in oxyallyl JCS,PT2 1998, 1037, Borden et al. Hartree-Fock for non-degenerate system energy B2 32 2

h2 + h3 + J23 K23 B2 32 2 h2 + h3 + J23 + K23 A1 33 2 A1 Triplet wave function 3 Singlet wave functions 1 1 1 2 2 2

2 3 3 2 2 3 3 2 h2 + h3 + (J22 + J33)/2 [K232 + {h2-h3+(J22-J23)}2]1/2 The ground state becomes 1A1 if J22 J23 + K23 < h3 h2 Oxyallyl anion : O + acetone reaction H3C O + C CH3 - H2O H2C O C CH2 O - H2O

HC C CH3 O MH2 ions oxyallyl radical anion carbene radical anion MH ion - OH H2C C O CH3 acetone enolate anion Photoelectron spectrum of MH ion OH + acetone reaction H2C 1200 Photoelectron counts 1000 radical radical C

CH3 O 800 MH 600 acetone enolate 400 JPC 1982, 86, 4873, Ellsion et al. 200 0 3.0 2.5 2.0 electron binding energy (eV) 1.5 Photoelectron spectrum of MH2 and MH ions O + acetone reaction H2C 1000 C O Photoelectron counts 800 HC 600 C

O 400 200 H2C 0 3.0 2.5 2.0 electron binding energy (eV) 1.5 C O CH2 MH2 CH3 MH2 CH3 MH Photoelectron spectrum of MH2 ion 1000 H2C photoelectron counts 800 600 400

C O detachment from O lone-pair orbitals HC 200 C O 0 3.0 2.5 2.0 electron binding energy (eV) 1.5 CH2 MH2 CH3 MH2 Photoelectron spectrum of MH2 ion oxyallyl 1200 1 X 1 A1 photoelectron counts 1000 a 3B2 A1

H 800 magic angle 0 degree 90 degree 600 C B2 H 2.4 2.2 2.0 1.8 electron binding energy (eV) EA = 1.945 0.010 eV 1.6 C H H O 200 0 C H 3

400 O C H Te (3B2) = 0.056 0.005 eV C C H H Franck-Condon simulation for the 3B2 oxyallyl diradical 350 photoelectron counts 300 CCC bending mode 400 20 cm-1 250 experiment (0 degree) Franck-Condon simulation 200 150 100 50 0 2.4 2.2 2.0 1.8 1.6

electron binding energy (eV) B3LYP/6-311++G(d,p) calculations on 2A2 anion and 3B2 neutral 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/6311++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 3B spectrum. This is assigned to the 1A ground state of oxyallyl. The 2 1 electron affinity of oxyallyl is 1.945 0.010 eV, and the term energy for the 3B state is 0.056 0.005 eV. 2 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

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