CYCLOPOLYMERIZATION OF ACETYLENE TO BENZYNE AND NAPHTHALENE
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Date
2012
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
Reactions of acetylene (C$_2$H$_2$) with laser-vaporized La atoms produced La(C$_6$H$_4$) and La (C$_{10}$H$_8$) in supersonic molecular beams. The organic fragments in these complexes were benzyne and naphthalene. The benzyne species was produced by the La-mediated cyclotrimerization of three acetylene molecules, whereas naphthalene was formed likely by the cyclization of the transient benzyne with two additional acetylene molecules. These cyclized products were identified by mass-analyzed threshold ionization mass spectroscopy, which measured adiabatic ionization energies and several vibrational frequencies. The measured ionization energies were 40875 (5) cm$^{-1}$ for La(C$_6$H$_4$) and 36767 (5) cm$^{-1}$ for La(C$_{10}$H$_8$). The most active vibrational transitions of both complexes were metal-ligand stretching with 326 cm$^{-1}$ for La(C$_6$H$_4$) and 286 cm$^{-1}$ for La (C$_{10}$H$_8$). By combining the spectra with theoretical calculations, the ground electronic states of the neutral complexes were determined to be $^2$A$_1$ (C$_{2v}$) and $^2$A$^\prime$ (C$_s$) and those of the corresponding ions were $^1$A$_1$ (C$_{2v}$) and $^1$A$^\prime$ (C$_s$) for La (C$_6$H$_4$) and La(C$_{10}$H$_8$), respectively.
Description
Author Institution: Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055