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Vibrational Spectrum of m-Benzyne:  A Matrix Isolation and Computational Study

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journal contribution
posted on 15.10.2002 by Wolfram Sander, Michael Exner, Michael Winkler, Andreas Balster, Angelica Hjerpe, Elfi Kraka, Dieter Cremer
m-Benzyne (2) was generated in low-temperature matrices and IR spectroscopically characterized from four different precursors. To assign the IR absorptions, the perdeuterated derivative 2-d4 was also investigated. By comparison with CCSD(T) calculations all vibrations between 200 and 2500 cm-1 with a predicted relative intensity >2% could be assigned. All experimental and theoretical results are in accordance with a biradicaloid structure for 2, while there is no evidence for a bicyclic closed-shell structure. While benzyne 2 is stable under the conditions of matrix isolation at low temperature, flash vacuum pyrolysis at high temperatures or UV irradiation results in the rearrangement to cis-enediyne. A mechanism involving ring opening accompanied by hydrogen migration is proposed.