Oxidative and electrophilic chemistry (protonation, acetylation, trimethylsilylation) of octamethylbiphenylene and dodecamethylbinaphthylene; a mass spectral and superacid solution study

Abstract

A mass spectral study of the cations formed by oxidation, protonation, acetylation (MeCO⁺), trimethylsilylation (Me₃Si⁺), and trifluoroacetylation–trifluoromethylation (CF₃CO⁺–CF₃⁺) of octamethylbiphenylene 4(fully methylated [2]phenylene) and dodecamethylbinaphthylene 5(fully methylated dibenzo[b,h] biphenylene) is reported, and the decomposition pathways of the resulting ions are probed by tandem mass spectrometry.

Collisional decompositions of the acylation and trimethylsilylation monocations are selective towards charge retention at the aromatic moiety. A bis-silylated monocation was formed via5. Doubly charged ions were only observed in oxidation reactions (El/MS).

The greater solution stability of the arenium ion of ipso protonation of 5 as compared to 4 is borne out by its direct observation in FSO₃H–SO₂CIF at low temperature.