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. The same does not occur in anthracene. While the 9-methylene derivative of anthracene is a local minimum, the planar 9-methyl derivative is the more stable. In the current study we investigate if certain derivatives of these anthracene systems stabilize the methylene system relative to the methyl, and if certain derivatives of these pentacene systems stabilize the methyl derivative relative to the methylene. Specifically, nitro and trifluoromethyl derivatives of anthracene are considered, and amino and methoxy derivatives of pentacene are examined. 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 the M06-2X high nonlocality hybrid functional from Thular and Zhao and the ωB97XD functional from Head-Gordan and coworkers which includes empirical dispersion. The basis sets employed are Dunning and coworkers’ correlation consistent basis sets cc-pVDZ and cc-pVTZ.

Relative stabilities of derivatives of 9-methylanthracene and 9-methylene-9,10-dihydroanthracene and derivatives of 6-methylpentacene and 6-methylene-6,13-dihydropentacene

ACS Spring Meeting 2021

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