Alkene Loss Research Articles

Synthesis and reactivity of (silox) 2R 2WO (R = Cl, Me, Et, nPr and nBu; silox = OSi tBu 3) and (silox) 2MO 2 (M = Mo and W)

Addition of Na(silox) (silox = OSi t Bu 3) to Cl 4WO afforded (silox) 2Cl 2WO ( 3), and subsequent alkylation with appropriate Grignard reagents yielded (silox) 2R 2WO ( 4-R; R = Me, Et, n Pr, n Bu). 4-R adopt distorted trigonal bipyramidal structures with axial silox groups, as implied by the X-ray crystal structure of 4- n Bu. New metathetical procedures were utilized in the preparation of (silox) 2M(O) 2 (M = Mo, 6; W, 7); the addition of Na(silox) to (DME)Cl 2M(O) 2 (M = Mo, W) in THF afforded the dioxo species. None of the oxo complexes exhibited oxygen atom transfer (OAT) to PMe 3. The thermolysis of 4-Et and 4- n Bu afforded olefin derivatives (silox) 2(ole)WO ( 5-ole; ole = C 2H 4, C 4H 8) as the primary products. Thermal degradation of (silox) 2(CD 3CH 2) 2WO ( 4-CH 2CD 3) revealed H/D-scrambling among α- and β-positions indicative of reversible β-H-elimination prior to alkane loss. A brief discussion of the lack of OAT is presented.

A dynamic dilution system-based evaluation of the procedure adopted for determining ozone precursor volatile compounds

A dynamic dilution system was created to evaluate the performance and the reliability of ozone precursor volatile organic compound (VOC) sampling ("TO-Can" canisters) and analysis (thermal desorption/gas chromatography/flame ionisation detection) techniques used by the "Laboratoire Interregional de Chimie du Grand Est (LIC)". Different atmospheres of VOCs were generated at concentrations between 0.8 and 25 ppb, with temperatures of 0, 10, 20 and 30 degrees C, and with relative humidities of 0, 30, 50, 70 and 90%. These conditions are generally representative of those commonly observed in ambient air in the eastern France. This dynamic dilution allows the simulation of a wide range of scenarios (concentrations, temperatures and relative humidities). After assessing the capacity and performance of the system, it was applied in order to evaluate the recoveries and stabilities of VOCs from canisters used for the collection and analysis of two mixtures of VOCs. The first mixture contained six alkanes (ethane, propane, butane, pentane, hexane and heptane), and the second contained five alkenes (ethene, propene, butene, 1-pentene and 1-hexene), five aromatics (benzene, toluene, ethylbenzene, m-xylene and o-xylene), acetylene, and 1,3-butadiene. No significant losses of alkanes from the canisters were observed after 21 days of storage, and good recoveries of alkanes from the canisters (>80%) were obtained regardless of the concentration, the temperature and the relative humidity. However, losses of certain aromatics were noted at low relative humidity.

In-Situ IR Spectroelectrochemistry Study of One-Electron Oxidations of Bis(cyclopentadienyl) Molybdenum(II)−Alkyne or −Alkene Compounds

Anodic oxidations of the bis-cyclopentadienyl alkyne compound MoCp2(η2-C2Ph2), 1, and three metal−alkene analogues MCp2(η2-C2H2 trans-R2) (M = Mo, R = CO2Me, 2; M = Mo, R = H, 3; M = W, R = H, 4) have been studied by a combination of electrochemistry and in-situ IR spectroelectrochemistry. The primary redox process for all compounds is a reversible one-electron oxidation at very facile potentials (from −0.30 V vs FeCp20/+ for 2 to −0.80 V for 4). The νCC alkyne stretch in the IR spectrum of 17-electron Mo−alkyne ion 1+ (1824 cm-1) was shifted 50 cm-1 to higher energy than the same band in 1, consistent with a decrease in the metal−alkyne interaction in the Mo(III) cation. Compounds 2−4 all gave Mo(III) cations that were stable on the cyclic voltammetry (CV) time scale. In bulk electrolyses monitored by a combination of voltammetric and in-situ IR spectroelectrochemical analyses, the Mo(III) cation 2+ was shown to undergo some loss of alkene. The fiber-optic in-situ IR technique is a powerful method for characterizing organometallic redox processes in which slow chemical reactions are coupled to the electron-transfer step.

Gas phase oxidation of alkoxo ligands in bis(peroxo)[MO(O2)2(OR)]? and trisoxo [MO3(OR)]? anions (M = Cr, Mo, W)

The anions [M(VI)O(O(2))(2)(OR)](-) and [M(VI)O(3)(OR)](-)(M = Cr, Mo, W; R = H, Me, Et, (n)Pr, (i)Pr) were transferred to the gas phase by the electrospray process. Their decomposition was examined by multistage mass spectrometry and collisional activation experiments. The molybdate and tungstate anions [M(VI)O(O(2))(2)(OR)](-) underwent parallel elimination of aldehyde (ketone) and dioxygen while the equivalent chromate underwent loss of dioxygen only. The peroxo ligands were the source of oxidising equivalents in both reactions. For each alkoxo ligand, the total yield of aldehyde for the tungstate system exceeded that for the molybdate system. Collisional activation of [M(VI)O(3)(OMe)](-) led to clean elimination of formaldehyde with the metal centre supplying the oxidising equivalents. For larger alkoxo ligands, only the chromate centre eliminated aldehyde, while the molybdate and tungstate centres underwent clean loss of alkene. Threshold activation voltages indicated that the peroxo ligands of [W(VI)O(O(2))(2)(OMe)](-) are more oxidising than the tungstate centre of [W(VI)O(3)(OMe)](-). (2)H and (18)O isotope tracing experiments were consistent with a formal hydride transfer mechanism operating for oxidation of alkoxo ligand in each system. In the solid state, anions [M(VI)O(O(2))(2)(OR)](-) are typically pentagonal pyramidal (oxo in apical site) while [M(VI)O(3)(OR)](-) are tetrahedral. The data indicate that an equatorial ligand position is the site of alkoxo oxidation in [M(VI)O(O(2))(2)(OR)](-) anions. Comparisons of the gas phase data with those for a solution phase system are made.

Density Functional Studies of Catalytic Alkane Dehydrogenation by an Iridium Pincer Complex with and without a Hydrogen Acceptor

AbstractFor Abstract see ChemInform Abstract in Full Text.

Kinetics of reactions of chlorine atoms with a series of alkenes at 1 atm and 298 K: structure and reactivity

Chlorine atoms are important oxidants at dawn in the marine boundary layer where a variety of organics are also present, including alkenes. Using the relative rate technique, the kinetics of the gas phase reactions of atomic chlorine with a series of alkenes, relative to n-heptane as a reference, have been investigated at (298 ± 3) K and 1 atmosphere in either synthetic air or nitrogen. The rate constant for n-heptane, relative to n-butane whose rate constant was taken to be 2.18 × 10−10 cm3 molecule−1 s−1, was also measured and found to be (3.97 ± 0.27) × 10−10 cm3 molecule−1 s−1 (2s). Based on this value for the n-heptane reaction, the following absolute values for the rate constants, k (in units of 10−10 cm3 molecule−1 s−1) for the chlorine atom reactions were determined: propene, 2.64 ± 0.21; isobutene, 3.40 ± 0.28; 1-butene, 3.38 ± 0.48; cis-2-butene, 3.76 ± 0.84; trans-2-butene, 3.31 ± 0.47; 2-methyl-1-butene, 3.58 ± 0.40; 2-methyl-2-butene, 3.95 ± 0.32; 3-methyl-1-butene, 3.29 ± 0.36; 2-ethyl-1-butene, 3.89 ± 0.41; 1-pentene, 3.97 ± 0.36; 3-methyl-1-pentene, 3.85 ± 0.35; and cis-4-methyl-2-pentene, 4.11 ± 0.55 (±2s). The errors reflect those in our relative rate measurements but do not include the 10% error in the absolute value of the n-butane rate constant upon which these rate constants are ultimately based. A structure–reactivity scheme is presented that assumes that rate constants for addition of chorine atoms to the double bond, as well as that for abstraction of an allylic hydrogen atom, depend upon the degree of alkyl substitution at the double bond and allylic carbons. The surprising result is that the allylic hydrogen atoms react less rapidly with chlorine atoms than the analogous alkyl hydrogens in alkanes. The atmospheric implications for loss of alkenes in the marine boundary layer are discussed.

Aqueous vapor extraction: a previously unrecognized weathering process affecting oil spills in vigorously aerated water.

Simple evaporation of spilled oil is usually thought to be restricted to the smaller hydrocarbons (<15 carbons). We show that aeration of oil in water, at 22 degrees C, substantially extends this evaporation, leading to the loss of alkanes up to at least hexatricosane (nC36) and of polycyclic aromatic hydrocarbons with at least four rings (e.g., chrysene and its alkylated forms). This phenomenon is apparently related to steam distillation and should be considered as an important candidate pathway to explain the observed weathering of oil spilled from the OSSA II pipeline into the Río Desaguadero on the Bolivian Altiplano (approximately 3700 m), which occurred during a very turbulent flood.

Density functional studies of catalytic alkane dehydrogenation by an iridium pincer complex with and without a hydrogen acceptor

Density functional calculations have been applied to models of both transfer and acceptorless alkane dehydrogenation for the iridium(III) pincer complex, ( R PCP )IrH 2 ( R PCP η 3 -C 6H 3(CH 2PR 2) 2-1,3). The iridium pincer complex is the first efficient homogeneous catalyst that does not require photons or sacrificial hydrogen acceptors to drive the reaction, although with the latter the transfer reaction can accomplished under mild conditions. There are four essential steps for the catalytic cycle in both transfer and acceptorless reactions: oxidative addition of alkane, reductive elimination, β-hydrogen (β-H) transfer, and loss of olefin. The transfer reaction can utilize a hydrogen acceptor to produce a 14-electron intermediate, ( R PCP )Ir(I), and the acceptorless reaction can produce an 18-electron intermediate, ( R PCP )Ir(V)(H) 3(alkyl) species. Because the critical barriers are well-balanced in the Ir(V) catalytic cycle for acceptorless alkane dehydrogenation, no transition state (TS) is higher in energy than the products and no intermediate is lower in energy than the reactant. This balance could explain why pincer complexes are more efficient catalysts for alkane dehydrogenation than the corresponding Cp–Ir(III) complex. Entropy contributions, which play a larger role at high temperature, open new pathways for the acceptorless reaction. Free energies of activation suggest that the dynamics of the acceptorless reaction might be sampling the entire range of pathways and Ir oxidation states from Ir(I) to Ir(V).

Palladium(II) beta-agostic alkyl cations and alkyl ethylene complexes: investigation of polymer chain isomerization mechanisms.

A series of stable dialkyl complexes of Pd, (alpha-diimine)PdR2 (alpha-diimine = aryl-substituted diimine, R = n-Pr, n-Bu, i-Bu), have been prepared via Grignard alkylation of the corresponding (alpha-diimine)PdCl2 complexes. Protonation of these dialkyl species at low temperature results in loss of alkane and formation of cationic Pd beta-agostic alkyl complexes, which have been observed as intermediates in the polymerization of ethylene and propylene by these Pd catalysts. Studies of the structure and dynamic behavior of these alkyl complexes are presented, along with the results of trapping reactions of these species with ligands such as NCMe, CO, and C2H4. Trapping with ethylene results in formation of cationic alkyl ethylene complexes which model the catalyst resting state in these systems. These complexes have been used to obtain mechanistic details and kinetic parameters of several processes, including isomerization of the alkyl ethylene complexes, associative and dissociative exchange with free ethylene, and migratory insertion rates of both primary and secondary alkyl ethylene species. These studies indicate that the overall branching observed in polyethylenes produced by these Pd catalysts is governed both by the kinetics of migratory insertion and by the equilibria involving the alkyl ethylene complexes.

Gas-Phase Reactivity of Copper Cations with Ketones

Gas-phase ion–molecule reactions between copper ions and ketones were investigated. Organometallic adducts were prepared using a chemical ionisation/fast-atom bombardment source. Abundant pseudo-molecular ion adducts were observed in the Cu+-chemical ionisation mass spectra and their unimolecular decompositions were studied by tandem mass spectrometry. Mass-analysed ion kinetic energy spectroscopy revealed diagnostic fragmentation patterns. Losses of alkenes, losses of alkanes and dehydrogenation and dehydration reactions were observed, as well as eliminations of CuR (R = C nH2 n + 1). The rich reaction chemistry of the cationised ketones enabled differentiation of the majority of the linear and branched ketone isomers studied. Isotope-labelled derivatives were employed to elucidate fragmentation mechanisms.

Investigation of the Mechanism of Alkane Reductive Elimination and Skeletal Isomerization in Tp‘Rh(CNneopentyl)(R)H Complexes: The Role of Alkane Complexes

Experiments are described that provide indirect evidence for the involvement of alkane sigma-complexes in oxidative addition/reductive elimination reactions of Tp'Rh(L)(R)H complexes (Tp' = tris-3,5-dimethylpyrazolylborate, L = CNCH(2)CMe(3)). Reductive elimination rates in benzene-d(6) were determined for loss of alkane from Tp'Rh(L)(R)H, where R = methyl, ethyl, propyl, butyl, pentyl, and hexyl, to generate RH and Tp'Rh(L)(C(6)D(5))D. The isopropyl hydride complex Tp'Rh(L)(CHMe(2))H was found to rearrange to the n-propyl hydride complex Tp'Rh(L)(CH(2)CH(2)CH(3))H in an intramolecular reaction. The sec-butyl complex behaves similarly. These same reactions were studied by preparing the corresponding metal deuteride complexes, Tp'Rh(L)(R)D, and the scrambling of the deuterium label into the alpha- and omega-positions of the alkyl group monitored by (2)H NMR spectroscopy. Inverse isotope effects observed in reductive elimination are shown to be the result of an inverse equilibrium isotope effect between the alkyl hydride(deuteride) complex and the sigma-alkane complex. A kinetic model has been proposed using alkane complexes as intermediates and the selectivities available to these alkane complexes have been determined by kinetic modeling of the deuterium scrambling reactions.

Field desorption mass spectrometry of large multiply branched saturated hydrocarbons.

Large multiply branched saturated hydrocarbons containing 67-103 carbon atoms (molecular masses 941.8-1446.8 Da) were analyzed by field desorption mass spectrometry (FD-MS) with a double-focusing mass spectrometer. FD-MS was found to have detection limits in the 100 fmol range. The FD mass spectra exhibited molecular ions of astonishingly low abundance. However, the fragment ions formed were closely related to the proposed molecular structure, allowing us to set up rules for straightforward structure elucidation of unknowns. In detail, (i) dehydrogenation, (ii) alkyl losses from molecular ions and (iii) subsequent alkene losses were observed. The influence of the electric field strength on dehydrogenation and C-C cleavages was examined by variation of the emitter potential. Additionally, ion dissociations in the ion source and in the first and second field-free regions, respectively, were compared to study the relative importance of field-induced and thermally induced processes.

Anthropogenic Sources of Chlorine and Ozone Formation in Urban Atmospheres

In this paper, we present ambient monitoring data from Houston, TX along with results from environmental chamber studies to suggest that molecular chlorine (Cl2), a photolytic source of chlorine atoms (Cl•), may contribute significantly to ozone (O3) formation in some urban environments. The ambient data were collected during an ozone episode in August 1993 that involved an alkane-rich hydrocarbon plume passing over anthropogenic sources of Cl2. Two unusual observations were made about the plume a few hours after it had passed over the Cl2 sources: (1) a rapid loss of alkanes and (2) a large increase in ozone concentration. Neither of these observations could be explained with models employing hydroxyl radical (OH•) chemistry (OH• are generally accepted to control oxidative chemistry in the daytime troposphere). Environmental chamber experiments were performed to determine whether the addition of Cl2 to a mixture of air, hydrocarbons, and nitrogen oxides (NOx) representative of conditions in the Houston ...

A density functional study on the formation of stereoerrors in the stereoselective propene polymerization with zirconocene catalysts

Abstract Recent labeling experiments have detected stereoerrors in the isotactic polymerization of propene with zirconocenium catalysts, which are characterized by a deuterium transfer from the polymer chain to a methyl group. Using Cp 2 Zr- iso -butyl + as a model system, two alternative mechanisms leading to the observed products are investigated using fully nonlocal levels of density functional theory (DFT). The direct hydrogen transfer starting from a γ-agostic intermediate requires an overall activation relative to the β-agostic resting state in excess of 200 kJ mol −1 and can be excluded. The sequential mechanism involves a (i) β-elimination to yield an initial iso -butene π-complex; (ii) a subsequent internal rotation of this π-complex; and (iii) reinsertion of the olefin into the ZrH bond via two consecutive formations of β-agostic interactions, with maximum relative energies along this path between 35 and 54 kJ mol −1 (depending on functionals and basis sets employed). The subsequent steps are the reverse of the first three steps and can lead to an inverted iso -butyl complex with migrated deuterium. Although certain barrier heights are somewhat sensitive to the density functional employed (BP86 vs. B3LYP), the sequential mechanism is much more favorable energetically. Loss of olefin from the intermediate π-complex is endothermic by 104–114 kJ mol −1 and should therefore not occur.

Cobaloxime π-Cation Steric and Stereoelectronic Effects: The Amazing Effect of a Single Methyl Group Adjacent to the Site of Reaction

Typically, β-hydroxylalkylcobaloximes are very sensitive to acid, readily forming transient cobaloxime π-cations which can either be trapped with nucleophiles or undergo irreversible alkene loss. Surprisingly, 2,3-dihydroxy-3,7-dimethyl-6-octenyl cobaloxime (1) was found to be stable to acid treatment, including that by the strong acid camphorsulfonic acid. A comparative study of the acid stability of 2,3-dihydroxypropyl cobaloxime (8), 2,3-dihydroxylbutyl cobaloxime (9), and 2,3-dihydroxy-3-methylbutyl cobaloxime (10) was done, showing that 8 and 9 exhibit normal acid sensitivity whereas 10 is stable to acid. The inclusion of an additional methyl group in going from 9 to 10 completely turns off an otherwise very facile reaction, presumably due to severe steric effects of the py(dmgH)2Co moiety of the cobaloxime which forces the acyclic chain of 10 to adopt a conformation which is stereoelectronically nonproductive for cobaloxime π-cation formation.

Reactions of trialkylgalliums with substituted hydrazines leading to the formation of rings and cages: X-ray structures of ( iPr 2GaNHNMe 2) 2 and (MeGaNHN tBu) 4

The reaction of trialkylgalliums with substituted hydrazines forms simple Lewis acid–base adducts at room temperature. Subsequent thermolysis of these adducts leads to step by step alkane loss forming first dimeric rings, then tetrameric cages. Thus the dimeric compounds [Me 2GaNHNMe 2] 2, [Et 2GaNHNMe 2] 2, [Me 2GaNHNPh 2] 2, [Et 2GaNHNPh 2] 2, [ i Pr 2GaNHNMe 2] 2, and [Me 2GaNHNH t Bu] 2, have been synthesized. In addition, [ i Pr 2GaNHNMe 2] 2 has been characterized crystallographically. Although exclusively in the anti conformation in the solid state, the dimers are fluxional in solution at room temperature. The fluxionality is examined in detail by NMR spectroscopy. The tetrameric [MeGaNHN t Bu] 4 has been isolated and crystallographically characterized. It is shown to have a cage structure consisting of two hexagonal and four pentagonal rings.

Ring versus oxygen protonation in metastable ion decompositions of protonated isopropyl phenyl ether

Protonated alkyl phenyl ethers possess more than one stable tautomer. A debate has arisen over whether only one of them gives rise to the principal dissociation pathway observed in their mass-analyzed ion kinetic energy (MIKE) spectra. Alkene loss constitutes the major (often the exclusive) metastable ion decomposition, yielding protonated phenol ions. A hydron deposited by chemical ionization exchanges with some of the alkyl hydrogens (but none of the ring hydrogens) prior to fragmentation. Previously published MIKE spectra have shown that [(CD 3) 2CHOPh]D + gives only m/ z 97 (C 6H 5D 2O +), but that [(CD 3) 2CHOPh]H + gives a mixture of m/ z 96 (C 6H 6DO +) and m/ z 97. Exchange must arise via ion-neutral complexes that result from O-protonated ions, (CD 3) 2CHO(H)Ph +. Current controversy centers around the contribution of ring-protonated ions to the production of unexchanged fragment ions. Here we determine the mole fractions of ring-protonated ( X) and O-protonated (1 − X) parent ions using m/ z 95: m/ z 96: m/ z 97 MIKE ion abundance ratios from H 2O and D 2O CI of (CH 3) 2CHOPh, CH 3(CD 3)CHOPh, and (CD 3) 2CHOPh. Data from the first two compounds give unbiased assessments of X and four other relative rate constants that are obtained using a steady-state kinetic model that gives a set of five equations in five unknowns. The values calculated from the data predict an m/ z 96: m/ z 97 ratio of 4.7 for [(CD 3) 2CHOPh]H + that turns out to be the same ratio as is measured experimentally. This validation of the data analysis corroborates the value of X ≤ 0.01 extracted from the experimental results. The contribution of ring-protonated parent ions to the MIKE spectra of chemically ionized isopropyl phenyl ether is therefore negligible.

Energetics of Homogeneous Intermolecular Vinyl and Allyl Carbon−Hydrogen Bond Activation by the 16-Electron Coordinatively Unsaturated Organometallic Fragment [Tp‘Rh(CNCH2CMe3)

Reaction of the complex Tp‘Rh(CNneo)(CHCH2)Cl (neo = CH2CMe3, Tp‘ = hydridotris(3,5-dimethylpyrazolyl)borate) with Cp2ZrH2 leads to the formation of Tp‘Rh(CNneo)(CHCH2)H. This complex is also formed upon photolysis of a solution of Tp‘Rh(CNneo)(PhNCNneo) containing ethylene or by thermal reaction of Tp‘Rh(CNneo)(c-hexyl)H with ethylene. The vinyl hydride complex rearranges to the more stable η2-ethylene complex with a half-life of 8 h at 22 °C. Photolysis of a solution of Tp‘Rh(CNneo)(PhNCNneo) in liquid propylene produces the allylic activation product Tp‘Rh(CNneo)(CH2CHCH2)H, which rearranges (t1/2 = 3 days at 22 °C) to the η2-propylene complex. Allylic activation is also seen with isobutylene, but loss of olefin is observed at 22 °C in benzene solution to generate Tp‘Rh(CNneo)(Ph)H (t1/2 = 16.6 h). Photolysis of a tert-butylethylene solution of Tp‘Rh(CNneo)(PhNCNneo) produces the trans vinyl hydride complex, which loses tert-butylethylene to generate Tp‘Rh(CNneo)(Ph)H (t1/2 = 113 days at 22 °C). A comb...

Gas-Phase Reactions of Fe(CH2O)+ and Fe(CH2S)+ with Small Alkanes: An Experimental and Theoretical Study

The gas-phase reactions of Fe(CH2O)+ and Fe(CH2S)+ with a series of aliphatic alkanes were studied by Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Like bare Fe+, C−C insertion, particularly terminal C−C insertion, is predominant for the reactions of Fe(CH2O)+, while C−H insertion is preferred for Fe(CH2S)+. About 90% of the Fe(CH2O)+ reaction products are formed by C−C insertion with small alkane loss. For Fe(CH2S)+, after initial C−H insertion, the proposed mechanism includes hydrogen transfer to sulfur, followed by migratory insertion of methylene into the metal−alkyl bond and formation of an activated H2S−Fe+−olefin complex, which dissociates by H2S elimination. The structures of the reaction products were probed by collision-induced dissociation, ion−molecule reactions, and use of labeled compounds, yielding information about the reaction mechanism. Collision-induced dissociation and ligand displacement reactions yield the brackets D0(Fe+−C3H6) = 37 ± 2 kcal/mol < D0(Fe+−CH2S) < D0(Fe+−C6H6) = 49.6 ± 2.3 kcal/mol and D0(Fe+−CH2O) < D0(Fe+−C2H4) = 34 ± 2 kcal/mol. The optimized geometry of Fe(CH2O)+, obtained by density functional calculations, has C2v symmetry with a nearly undisturbed formaldehyde unit. The Fe+−CH2O bonding is found to be predominantly electrostatic with a calculated bond energy of 32.2 kcal/mol. However, the optimized Fe(CH2S)+ structure has Cs symmetry with dative bonding between Fe+ and CH2S. D0(Fe+−CH2S) is calculated at 41.5 kcal/mol. The differences in geometry and chemical bonding between Fe(CH2O)+ and Fe(CH2S)+ are correlated with the different reaction pathways observed.

Ion-Neutral Complexes of Protonated Alkylbenzenes: Experimental and Theoretical Studies

In the gas phase, the unimolecular reactions of metastable protonated alkyl arenes lead to alkyl cation formation with arene loss, protonated arene formation with alkene loss, and benzylic cation formation with alkane elimination. The dissociations are often preceded by an exchange between the hydrogen atoms of the chain and those of the ring, which can be rationalized by an interconversion between [arene alkyl cation] and [protonated arene alkene] ion-neutral complexes. By comparing the reactions of the metastable protonated alkyl arenes and those of their isomeric adducts (arene/alkyl cation) generated in the ion source by ionmolecule reaction, we show that n-complexes [arene alkyl cation] have a significant lifetime. By ab initio calculations, [C6H6 iso-C3H7+] and [C6H7+ C3H61 ion-neutral complexes are shown to be energy minima on the potential energy surface. They correspond therefore to stable structures. Two methods, namely, ab initio and semiempirical calculations, are used to calculate the interaction energies of [arene alkyl cation] complexes. The smallest stabilization energy (49 kJ/mol) corresponds to [C6H6 tert-CJ-b+] and the largest (65 kJ/mol) corresponds to [P-CH3Cd-I&H3 iso-C3H7+]. The [protonated arene alkene] complexes are less stabilized (ca. 25 kJ/mol). The calculations also indicate that [arene alkyl cation] complexes have n-structures, but do not correspond to electron donor-acceptor (EDA) systems since, among the components of their interaction energy, the charge exchange term is negligible. Finally, these results are used to propose energy diagrams and fragmentation pathways.