Synthesis, Crystal Structure, and Explosive Decomposition of 1,2:5,6:11,12:15,16-Tetrabenzo-3,7,9,13,17,19-hexadehydroannulene: Formation of Onion- and Tube-like Closed-Shell Carbon Particles.
Oxidative coupling of bis(2-ethynylphenyl)ethyne gives the title annulene (I, R = H), the corresponding trimer, hexabenzononadehydroannulene, and a pentamer, decabenzopentadehydroannulene. X-ray and NMR anal. of I (R = H) shows it to be a nonplanar, unstrained, and chiral, but rapidly enantiomerizing mol. The synthesis of I (R = Me2CH) allowed the detn. of the barrier to enantiomerization through a planar structure: 9.3 kcal/mol-1. All of these compds. explode violently on heating. A detailed examn. of this decompn. focused on I (R = H): 245 Deg dec.; DH = -95 kcal/mol-1 (DSC); 10% mass loss (TGA); evolved gases: CH4 and H2 (Raman spectroscopy, gas phase NMR); LD-FTMS indicates oligomerization with loss of H2 and CH4. TEM anal. of the essentially pure carbon residue revealed extensive formation of ordered carbon layers of tube- and onion-type, in addn. to graphite and amorphous carbon. This observation suggests exploration of this novel process in the designed construction of carbon allotropes.
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