Fragmentation of arylated medium-ring compounds. The question of rearrangement of molecular-ion precursors to [C4Ar4]+˙

Rearrangement of the molecular ions of tetracyclone, tetraphenylquinone, tetraphenylthiophene dioxide and pentaphenylcyclopentadienol prior to decomposition, rather than formation of a symmetrical C₄Ar₄]⁺˙ ion, is considered as an alternative method for the production of C₂Ar₂]⁺˙. The p-fluoro substituent is used to elicit information about the positional origins of the C₂Ar₂]⁺˙ fragments. Operation of a double focusing mass spectrometer in the defocused mode reveals that the integrity of the molecular ion in different systems is affected to varying degrees, ranging from total lack of rearrangement to virtually complete scrambling.