Isomerization reaction of [C₆H₆ C₄H] π complexes

Abstract

,J ionheutral complexes is demonstrated. Protonated t-butylbenzene reacts without hydrogen exchange to give t-C4HT, while protonated n-butylbenzene isomerizes to s-butylbenzene prior to dissociation. Protonated iso-butylbenzene isomerizes to protonated t-butylbenzene and to protonated s-butylbenzene. In the 2nd field-free region, the dissociation of this last form predominates.

Protonated 1,3,5-cycloheptatriene and 7-alkyl-1,3,5-cycloheptatrienes in the gas phase: ring contraction to the isomeric alkylbenzenium ions

“…Fragmentation of metastable n-propyl-and isopropyldihydrotropylium ions and their labelled analoguesa 34 However, and in agreement with the Ðndings of ethyldihydrotropylium ions (see above), the mobility of the tertiary hydrogen at the a position of the isopropyl group is clearly enhanced, as evident from the ratios of and (ca. 1 : 1) and also of and…”

Crucial Role of Elusive Isomeric η-Complexes in Gas-Phase Electrophilic Aromatic Alkylations

“…Since Dewar's proposal in 1946, the role of the electrostatically bound π-complex in electrophilic aromatic substitutions has been examined thoroughly in both the gaseous − and condensed phases. , In the nineties, first Audier's 19 and later Gross' group 19 (A&G) provided convincing mass spectrometric evidence that σ-intermediates from the gas-phase protonation of alkylarenes may coexist with the corresponding electrostatically bonded alkyl cation/arene π-complexes. These findings, coupled with the insight gained from other related work, led A&G to formulate a refined model for gas-phase electrophilic aromatic substitutions whose reaction coordinate may involve the formation of an early π-adduct which eventually collapses to a σ-complex.…”

Concomitant Hydride and Proton Transfer: An Essay on Competing and Consecutive Key Reactions Occurring in Gaseous Ion/Neutral Complexes

“…3 However, in spite of the fact that hydride transfer from the analyte molecule to a reactant ion of the CI plasma as the origin of the quasi-molecular ions [M − H] + had been discussed from the very beginning, 3 proton transfer generating the quasi-molecular ions [M + H] + and protoninduced fragmentation has always dominated the focus of research and general understanding of the CI process. [4][5][6][7][8][9][10][11][12][13][14][15][16][17] In this essay, we focus on the gas-phase ion chemistry of alkylbenzenes and related compounds, which has been subject of intense research in CI mass spectrometry. 4 Although a large number of reports discuss the fragmentation of longlived protonated species of this class of compounds, [12][13][14][15][16][17][18][19][20] the first report demonstrating the fragmentation of metastable ions by hydride abstraction appeared no earlier than 1990, as a communication by Audier and his associates.…”

“…[4][5][6][7][8][9][10][11][12][13][14][15][16][17] In this essay, we focus on the gas-phase ion chemistry of alkylbenzenes and related compounds, which has been subject of intense research in CI mass spectrometry. 4 Although a large number of reports discuss the fragmentation of longlived protonated species of this class of compounds, [12][13][14][15][16][17][18][19][20] the first report demonstrating the fragmentation of metastable ions by hydride abstraction appeared no earlier than 1990, as a communication by Audier and his associates. 21 Notably, the observation of hydride transfer provided much more convincing evidence for the intermediacy of ion/neutral complexes during the fragmentation of protonated alkylbenzenes than any of the known proton transfer processes did.…”