[4]Annulene. Comments on its infrared spectrum

Masamune, Satoru; Sugihara, Yoshikazu; Morio, Kazuhiko; Bertie, John E.

doi:10.1139/v76-379

Cited by 16 publications

(6 citation statements)

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“…A report6 of a different broad and weak absorption band at 405 nm was later disproved. 10 We find that after the irradiation of 2 at 248 nm and subsequent bleaching with 254-and 313-nm light to destroy 3-5, the matrix contains CO, CO2, acetylene, and appreciable quantities of 1 as evidenced by its IR spectrum (vide infra). UV-visible and infrared spectra obtained on the same sample, deposited on a sapphire deposition window, show no observable UV-visible band maximum above 230 nm, even though bands known to belong to 1 are observable in the infrared ( Figure 1).…”

Section: Resultsmentioning

confidence: 81%

Ultraviolet and polarized infrared spectroscopy of matrix-isolated cyclobutadiene and its isotopomers

Arnold¹,

Michl²

1993

J. Phys. Chem.

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The UV and polarized IR spectra of argon matrix isolated cyclobutadiene and its I-d-, 1,2-d2-, 1,4-d2-, I%", l,2-W2-, and I,I-W2-1abeled derivatives are reported. Above 250 nm, the UV spectrum contains no peaks with an extinction coefficient larger than 10 L M-l cm-l, but a weak absorption tail extends throughout the UV region. The absorption rises abruptly below 250 nm. The IR peak positions mostly agree with previous reports where these are available. Photoalignment studies support the symmetry assignment of fundamental vibrations and prove that the twoKekuld forms interconvert rapidly even at 10 K. Thespectral and photochemical effects of the presence of an adjacent C02 molecule in the cyclobutadiene matrix site are elucidated. Its presence causes a substantial retardation of the photofragmentation of cyclobutadiene into two acetylenes. This is attributed to accelerated vibrational energy loss from the cyclobutadiene absorber.Few molecules have sustained the interest of experimental and theoretical chemists as has cyclobutadiene (1). Since it was first P 1 2 3 4 s postulated,2 reports of the properties of this molecule have been shrouded in controversy, which has yet to be fully r e s~l v e d .~~~ There have been numerous spectroscopic studies that have revealed much about its properties,3--1° although it was only observed at low temperature in glasses or inert gas matrices until recently.11-13 In spite of this considerable effort, too few of the fundamental vibrations of 1 and its isotopomers are known presently to establish its force field. Its UV-visible spectrum has yet to be unambiguously let alone assigned. The rate of valence tautomerism, a process that is believed to occur mainly through heavy atom tunneling,1c19 has yet to be measured.Matrix effects have complicated the assignments of both the IR and UV spectra. In particular, side products, produced along with 1 and trapped within the same matrix cavity, have interfered with the identification of fundamental vibrations. The nature of the interactions between 1 and these companion molecules is unknown.We now report UV and IR spectra of 1 and its isotopically labeled derivatives, permitting us to settle some of these disputes. Polarized IR spectroscopy on samples partially oriented by photoselection has allowed an unambiguous symmetry assignment of the observed vibrations as in-plane or out-of-plane polarized and contributed to the identification of others. This approach has also confirmed the occurrence of rapid interconversion between the two valence tautomeric rectangular forms in low-temperature matrix environment and has yielded information concerning many of the puzzling aspects of the cyclobutadienematrix partner interactions.A brief communication of some of the present results has appeared. 8 ~ *Abstract published in Advance ACS Abstracts, November 1, 1993. Experimental SectionThe anhydride precursor (2) was synthesized using a modified version of a previously reported synthetic method.20J1 A lowtemperature Pyrex immersion photolysis vessel (Ac...

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Section: Resultsmentioning

confidence: 81%

Ultraviolet and polarized infrared spectroscopy of matrix-isolated cyclobutadiene and its isotopomers

Arnold¹,

Michl²

1993

J. Phys. Chem.

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“…It is Scheme 18. Photochemical Formation of Cyclobutadiene Using Various Precursors Such as Compounds 106, 127,320−323 108, 326 109, 318 110, 327 111, 319,324,325 112, 328 113, 326,327 114, 332 115, 331 116, 330 117, 334 and 118 329 particularly noteworthy that one of the new π-bonds formed is part of the CBD ring. Precursor 114, on the other hand, is interesting as the Fe(CO) 3 fragment formed upon decomposition is not a stable molecule, and both the CBD and Fe(CO) 3 products were only detected as short-lived intermediates by kinetic mass spectrometry.…”

Section: Photochemical Routes To 4π-electron (Hetero)annulenic Speciesmentioning

confidence: 99%

“…Scheme 18. Photochemical Formation of Cyclobutadiene Using Various Precursors Such as Compounds 106, 127,320−323 108,326 109, 318 110,327 111,319,324,325 112,328 113,326,327 114,332 115,331 116,330 117,334 and 118329 and the Weakly Bound T-Shaped Acetylene Dimer Complex 119333 Chemical Reviews…”

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confidence: 99%

Excited State Aromaticity and Antiaromaticity: Opportunities for Photophysical and Photochemical Rationalizations

et al. 2014

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“…[89][90][91][92][93] The most recent measurement of the UV absorption spectrum of argon-matrix isolated cyclobutadiene was reported by Michl's group. 93 It shows only one intense peak around 200 nm ͑6.2 eV͒; however, a weak absorption tail extends up to about 500 nm ͑2.5 eV͒.…”

Section: B Vertical and Adiabatic Excitation Energies Of Cyclobutadienementioning

confidence: 99%

Equation-of-motion spin-flip coupled-cluster model with single and double substitutions: Theory and application to cyclobutadiene

Levchenko

Krylov

2004

The Journal of Chemical Physics

331

352

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While the equation-of-motion coupled-cluster (EOM-CC) method is capable of describing certain multiconfigurational wave functions within a single-reference framework (e.g., open-shell type excited states, doublet radicals, etc.), it may fail in cases of more extensive degeneracy, e.g., bond breaking and polyradicals. This work presents an extension of the EOM-CC approach to these chemically important situations. In our approach, target multiconfigurational wave functions are described as spin-flipping excitations from the high-spin reference state. This enables a balanced treatment of nearly degenerate electronic configurations present in the target low-spin wave functions. The relations between the traditional spin-conserving EOM models and the EOM spin-flip method is discussed. The presentation of the formalism emphasizes the variational properties of the theory and shows that the killer condition is rigorously satisfied in single-reference EOM-CC theories. The capabilities and advantages of the new approach are demonstrated by its application to cyclobutadiene.

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[4]Annulene. Comments on its infrared spectrum

Cited by 16 publications

References 0 publications

Ultraviolet and polarized infrared spectroscopy of matrix-isolated cyclobutadiene and its isotopomers

Ultraviolet and polarized infrared spectroscopy of matrix-isolated cyclobutadiene and its isotopomers

Excited State Aromaticity and Antiaromaticity: Opportunities for Photophysical and Photochemical Rationalizations

Equation-of-motion spin-flip coupled-cluster model with single and double substitutions: Theory and application to cyclobutadiene

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