In 1949, Clar and Wright reported that 6-methypentacene exists as 6-methylene-6,13-dihydropentacene at room temperature due to a [1,5]-sigmatropic hydrogen shift. Thus, the aromaticity of the central ring and the planarity of the overall compound is destroyed by this shift.[1] Derivatives of the two parent isomers are investigated to determine if certain substituents can further stabilize the methylene isomer and if different substituents can stabilize the methyl isomer in which the overall planarity of the rings is maintained. The latter is especially important because synthesis of derivatives of alkyl-substituted pentacenes is rare.[2] Specifically, diamino, dinitro, tetraamino, and tetranitro derivatives are investigated. Optimum equilibrium geometries, harmonic vibrational frequencies, and the corresponding zero-point vibrational energies are computed for each set of isomers using density functional theory. The DFT functionals employed are ?B97XD and M06-2X. The basis set is Dunning and coworkers' correlation consistent basis set aug-cc-pVTZ. We gratefully acknowledge support from the NSF (EPS-0903787) and the W.M. Keck Foundation.References:1. E. Clar and J. Wright; Nature 163 (1949) 921.2. T. Takahashi, s. Li, W. Huang, F. Kong, K. Nakajima, B. Shen, T. Ohe, and K. Kanno; Journal of Organic Chemistry 71 (2006) 7967-7977.

Relative stabilities of derivatives of 6-methylpentacene and 6-methylene-6,13-dihydropentacene

247th National Meeting (2014)

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