Spectroscopic Identification of the Resonance-Stabilized cis- and trans-1-Vinylpropargyl Radicals

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• 作者：Neil J. Reilly ; Masakazu Nakajima ; Tyler P. Troy ; Nahid Chalyavi ; Kieran A. Duncan ; Klaas Nauta ; Scott H. Kable ; Timothy W. Schmidt
• 刊名：Journal of the American Chemical Society
• 出版年：2009
• 出版时间：September 23, 2009
• 年：2009
• 卷：131
• 期：37
• 页码：13423-13429
• 全文大小：238K
• 年卷期：v.131,no.37(September 23, 2009)
• ISSN：1520-5126

文摘

The cis-1-vinylpropargyl (cis-1VPR, cis-pent-4-en-1-yn-3-yl) and trans-1-vinylpropargyl (trans-1VPR, trans-pent-4-en-1-yn-3-yl) radicals, produced in a supersonically cooled hydrocarbon discharge, have been identified by a synergy of 2-dimensional fluorescence and ionization spectroscopies, revealing their electronic origin transitions at 21232 and 21645 cmp>−1p> respectively. These assignments are supported by an excellent agreement between calculated ground state frequencies of cis-1VPR and trans-1VPR with those obtained by dispersed fluorescence spectroscopy. In addition, high-resolution rotational contours of the two bands are well simulated using calculated - and -state trans-1VPR and cis-1VPR rotational constants. Finally, computed origin transition energies of these two isomers are within several hundred wavenumbers of the observed band positions. With the 1-phenylpropargyl radical, the 1VPR isomers are the second 1-substituted propargyl species to have been observed abundantly from a hydrocarbon discharge, while no 3-substituted analogue has been positively identified. This is likely due to the greater resonance stabilization energy of the 1-substituted species, arising from concerted delocalization of the unpaired electron over the vinyl and propargyl moieties.