Benzyne (C6H4) adds across the 9,10 positions of anthracene (C14H10) in a [4+2] cycloaddition. The molecular formula of the adduct (triptycene) is

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Benzyne ( $C X_{6} H X_{4}$ ) adds across the 9,10 positions of anthracene ( $C X_{14} H X_{10}$ ) in a [4+2] cycloaddition. The molecular formula of the adduct (triptycene) is

A cycloaddition combines the two molecules without loss of atoms, so the formulas add:

C X_{6} H X_{4} + C X_{14} H X_{10}

gives

C X_{20} H X_{14}

. The benzyne ring ends up as the third blade of the triptycene skeleton.