Structural Elucidation of Isomeric Bianthryls Generated from Anthracene Pyrolysis

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Abstract
Among the primary products of anthracene pyrolysis at 1213 K are the six isomeric bianthryls, which we have analyzed by high performance liquid chromatography with diode-array detection (HPLC/DAD), ultraviolet spectroscopy, and gas chromatography-mass spectrometry (GC-MS). When separated by reverse-phase HPLC or GC, the isomers elute in the order A,B,C,D,E,F, and only the elution orders of isomers C and D are reversed in normal-phase HPLC. Analysis of our product mixture after spiking with a 9,9″-bianthryl reference standard shows that A is 9,9″-bianthryl. The distinctive ultraviolet spectrum of 2,2″-bianthryl, the only isomer whose anthracene moieties are coplanar, confirms the identity of F as this bianthryl. Theoretical and experimental information in the literature on the effect of substituents on anthracene's ultraviolet absorption spectrum provides valuable guidance in interpreting the ultraviolet spectra of the bianthryls. Certain features of these spectra, combined with the principles governing chromatographic elution order, lead to the identification of the remaining bianthryls as: B, 1,9″-bianthryl; C, 2,9″-bianthryl; D, 1,1″-bianthryl; and E, 1,2″-bianthryl.

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