EVIDENCE FOR FAST AUTOMERIZATION BY 1,3-CYCLOBUTADIENE
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Date
1998
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Ohio State University
Abstract
MO computations of vibrational spectra for 1,3-cyclobutadiene (CB) isotopomers at the MP2/6-311++G (2d, 2p) level of MO theory are analyzed together with the Ar/CB matrix-isolation spectra of the Michl group, the low 4.8 kcal/mol MC-computed energy of the square-planar saddle-point for CB reported by Nakamura et al., and one-dimensional analyses of the automerization energy levels. The composite interpretation results in the assignment of the Raman transitions of Ar/CB observed at 723 and $1678 cm^{-1}$ to the $E_{1} - E_{0}$ and $E_{2} - E_{0}$ transitions, respectively, in the automerization coordinate. The PEF along the automerization coordinate crosses the $D_{4h}$ square-planar configuration at a dilated geometry with an energy about 1 - 2 kcal/mol higher than that of the saddle-points. The analysis of C3 vibrational behavior incorporates comparative behavior by the $CB:CO_{2}$ van der Waals molecule.
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Author Institution: Department of Chemistry and Biochemistry, Texas Tech University