Triarylmethyl cations eliminate substituted benzene in the gas phase, upon activation. The mechanism of this process has been studied using deuterium labeling, substituent effects, and density functional theory calculations. It is shown that this apparently simple dissociation is in fact a complicated stepwise process that involves several consecutive hydride shifts. . Trityl cations are generated from alcohols in acidic conditions, but they can also be generated from trityl halides in the presence of alkali metal, alkaline earth metal ions [6], or Lewis acids. A useful tool for the study of ionic species like trityl cations is gas-phase ion chemistry using mass spectrometry. Mass spectrometry has been used to understand dissociation kinetics and mechanisms of gas-phase molecular ions. Fragmentation pathways of molecular ions are determined using tandem mass spectrometry (MS/MS) isotopic labeling and molecular orbital calculations that provide valuable information. Owing to its general importance to synthetic organic chemistry, a large body of knowledge on the chemistry of cationic aromatic compounds, like alkylbenzenium ions and benzyl cations has been accumulated in the past four decades. For example, the production of C 7 H 7 ϩ from toluene molecular ion is one of the most extensively studied reactions in the field of gas-phase ion chemistry [7]. Other studies concentrate on protonation, ion-neutral complex formation, and H/D exchange processes in aromatic systems. See for example [8] and references cited therein.Electron ionization spectra of several trityl compounds were recorded by Shupe and Berlin [9]. The authors show several typical fragmentation pathways, the most abundant being the formation of a trityl cation. Another characteristic of these EI spectra is the presence of an ion at m/z165 that corresponds to the loss of 78 Da from the trityl cation of m/z 243. The authors suggest that the resulting ion of m/z 165 is a 9-fluorenyl cation. It is also known that benzhydryl cations can afford an analogous ion by the loss of H 2 [10]. The loss of molecular hydrogen is supported by the presence of a metastable ion.Triphenylmethane has also been studied with nega-Ϫ ion. Upon high-energy collisional activation, two major dissociation processes occur, involving the losses of C 2 H 4 and C 6 H 6 neutral fragments. The authors suggest that the loss of C 6 H 6 , a benzene ring, results in the formation of a 9-fluorenyl anion. Isotopic labeling experiments indicate extensive hydrogen-deuterium scrambling within this process [11].Modern desorption techniques enable the generation of stable trityl cations under relatively mild conditions. In the present work, we studied the characteristic loss of benzene or substituted benzene molecules from trityl cations. A detailed mechanism for the formation of 9-fluorenyl cation is proposed and supported by experimental work and theoretical calculations. Results and DiscussionProtonated trityl alcohols eliminate water readily affording trityl cations, under chemical ionization...