3,4-Benzocyclodeca-3,7,9-triene-1,5-diyne (3) has been synthesized fro
m two different precursors and characterized by means of matrix-isolat
ion spectroscopy. Energies, structures and IR spectra of the product,
the intermediate 9,10-didehydroanthracene (4), and of the transition s
tate of the Bergman cyclization 3 --> 4 have been calculated at the B3
LYP/6-31G level of theory.