The Aromaticity of Pyracylene: An Experimental and Computational Study of the Energetics of the Hydrogenation of Acenaphthylene and Pyracylene

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• 作者：Hermí ; nio P. Diogo ; Tetsu Kiyobayashi ; Manuel E. Minas da Piedade ; Natan Burlak ; Donald W. Rogers ; Daniel McMasters ; Gabriele Persy ; Jakob Wirz ; and Joel F. Liebman
• 刊名：Journal of the American Chemical Society
• 出版年：2002
• 出版时间：March 6, 2002
• 年：2002
• 卷：124
• 期：9
• 页码：2065 - 2072
• 全文大小：108K
• 年卷期：v.124,no.9(March 6, 2002)
• ISSN：1520-5126

文摘

In this work, the aromaticity of pyracylene (2) was investigated from an energetic point of view.The standard enthalpy of hydrogenation of acenaphthylene (1) to acenaphthene (3) at 298.15 K wasdetermined to be -(114.5 ± 4.2) kJ mol^-1 in toluene solution and -(107.9 ± 4.2) kJ mol^-1 in the gasphase, by combining results of combustion and reaction-solution calorimetry. A direct calorimetricmeasurement of the standard enthalpy of hydrogenation of pyracylene (2) to pyracene (4) in toluene at298.15 K gave -(249.9 ± 4.6) kJ mol^-1. The corresponding enthalpy of hydrogenation in the gas phase,computed from the _f(cr) and _sub values obtained in this work for 2 and 4, was -(236.0 ± 7.0) kJmol^-1. Molecular mechanics calculations (MM3) led to _hyd(1,g) = -110.9 kJ mol^-1 and _hyd(2,g) =-249.3 kJ mol^-1 at 298.15 K. Density functional theory calculations [B3LYP/6-311+G(3d,2p)//B3LYP/6-31G(d)] provided _hyd(2,g) = -(244.6 ± 8.9) kJ mol^-1 at 298.15 K. The results are put in perspectivewith discussions concerning the "aromaticity" of pyracylene. It is concluded that, on energetic grounds,pyracylene is a borderline case in terms of aromaticity/antiaromaticity character.