Carbon-13 NMR and polarized IR spectra of vicinally labeled cyclobutadiene-13C2 in an argon matrix: interconversion of valence tautomers

Orendt, Anita M.; Arnold, Bradley; Radziszewski, Juliusz G.; Facelli, Julio C.; Malsch, K.-D.; Strub, Henri; Grant, David M.; Michl, Josef

doi:10.1021/ja00216a049

Cited by 74 publications

(59 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…18 The out-of-plane bending vibration is observed to have positive dichroism, while all in-plane vibrations are observed to have negative dichroism. This result confirms the assignment of the 576-cm-1 vibration in the unlabeled species to the out-of-plane polarized b3" transition.…”

Section: Resultsmentioning

confidence: 95%

“…Besides the known fundamentalsof 1 at 576,721,1245, and 1526 cm-1, two bands at 3124 and 3107 cm-1 are clearly observed. 18 These are assigned as the bl, C-H stretch and the bz, C-H stretch, respectively, on the basis of the calculated frequencies and intensities.25 These two stretches were also assigned at 3073 and 3 105 cm-l when a tricyclic precursor was used.& While the 3 107-and 3 105-cm-1 assignments appear identical, we have no explanation for the discrepancy between this report and our observation of the other stretch at 3124 cm-'.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

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

Arnold¹,

Michl²

1993

J. Phys. Chem.

Self Cite

View full text Add to dashboard Cite

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...

show abstract

Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

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

Arnold¹,

Michl²

1993

J. Phys. Chem.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Aber selbst wenn man von diesen Schwierigkeiten absieht, sind Reaktionen dünn gesät, bei denen Hinweise auf einen SchweratomTunneleffekt vorliegen, und die angeführten Beispiele sind zumindest umstritten (siehe Lit. [15][16][17][18][19] für eine Diskussion von Schweratom-Tunneleffekten in der Cyclobutadien-Automerisation (Lit. [20]) und die etwas skeptischere Sicht in Lit.…”

Section: Derkürzestewegzueinemtalaufderunclassified

Sehen schwere Kerne Licht am Ende des Tunnels?

Berger

2004

Angewandte Chemie

View full text Add to dashboard Cite

show abstract

“…However, the best high-level ab initio calculations predict the barrier to lie between 27 and 32 kJ mol À1 . [31,32] These two facts can only be reconciled if one invokes heavy-atom tunnelling. In 1983 Carpenter had in fact done exactly that to account for the negative entropy of activation which he had deduced from his experiments, [29] and he concluded that the tunnelling mechanism would actually dominate the automerization process at temperatures below 0 8C.…”

mentioning

confidence: 99%