Structures and Stabilities of C5H2 Isomers: Quantum Chemical Studies

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• 作者：Randal A. Seburg ; Robert J. McMahon ; John F. Stanton ; and Jü ; rgen Gauss
• 刊名：Journal of the American Chemical Society
• 出版年：1997
• 出版时间：November 5, 1997
• 年：1997
• 卷：119
• 期：44
• 页码：10838 - 10845
• 全文大小：190K
• 年卷期：v.119,no.44(November 5, 1997)
• ISSN：1520-5126

文摘

Five isomers of the carbon-rich moleculeC₅H₂ are investigated computationally, usingmethods based onthe coupled-cluster approximation. All of these structures arerelated to isomers of C₃H₂ via substitution ofhydrogenby ethynyl or attachment of a C₂ fragment to a carbenecenter. The two most stable forms of C₅H₂are linear tripletpentadiynylidene (4) and singlet ethynylcyclopropenylidene(6). Both of these isomers have been observed inthelaboratory, as has a third-the cumulene carbene pentatetraenylidene(5)-which is predicted to lie about 15 kcal/mol above the linear triplet. Two other isomers are also studied:ethynylpropadienylidene (7) and 3-(didehydrovinylidene)cyclopropene (8). Both are found to lieless than 25 kcal/mol above the most stable form ofC₅H₂ andto possess rather large dipole moments. Predictions for theharmonic vibrational frequencies of ¹²C andmono-¹³Cisotopomers, infrared intensities, and rotational constants are alsopresented. These should assist efforts to identifythese molecules in the laboratory and in the interstellarmedium.