Toluene Ions Research Articles

Photofragmentation of toluene in a fourier transform-mass spectrometer in the visible and infrared range

The photodecomposition of the toluene ion has been measured in the visible and IR range (10 μm). Three isomers of C 7H + 8 can be distinguished, only two of them fragmenting in the IR range by loss of a hydrogen atom. One of them, the toluene ion, has to pass over an excited state that we tentatively identify as an excited cycloheptatriene radical cation. The other decomposing isomer most probably has a cycloheptatriene structure. Part of the C 7H + 7 ions fragments with visible light (488 nm) in a two-photon process; it is identified as benzyl ion. Tropylium is stable in this wavelength range. The dependence of these processes on the ionizing conditions, their rate constants and, where feasible, their induction time are determined. It is shown that the ratio benzylium/tropylium may depend on the cell conditions such as the filament current.

Concerning the fragmentation of ortho,ortho‐dimethyl substituted alkylbenzenes induced by γ‐H migration

Two recent paper 1,2 describe the McLafferty reaction of n-alkylbenzenes 3 1 without taking notice of the well-established existence of distonic ions 1a +. [4] as crucial intermediates. From a PEPICO/RRKM investigation of n-butylbenzene, Baer et al. 1 invoked the formation of an intermediate species during the elimination of propene. Kingston et al. 2 reported on the occurrence of the McLafferty reaction of a number of ionized (iso-pentyl)-benzenes bearing two methyl groups in the ortho positions. The latter finding is highly remarkable because it contradicts a long-standing 'dogma', 2 according to which this fragmentation channel is sterically blocked by 2,6-dimethyl substitution. 5 The blocking effect provided a strong argument in favour of the migration of the γ-H atom to one of the ortho positions of the aromatic ring and the formation of C 7 H 8 +. ions having the structure of 5-methylene-1,3-cyclohexadiene (ortho-isotoluene, Scheme 1), instead of toluene or cycloheptatriene ions. 3,5

ChemInform Abstract: Aromatic Nitration in Aqueous Nitric Acid

The rates of nitration of benzene, toluene, p-xylene, and mesitylene have been determined in aqueous nitric acid at concentrations between 24–41 mol % HNO3 and at temperatures between 293–333 K. Plots of log10(k1/aHNO3)versus–H0, where k1 is the pseudo-first-order rate constant, aHNO3the activity of the nitric acid, and H0 the Hammett acidity function, are linear, and confirm that the mechanism of nitration in aqueous nitric acid is similar to that in aqueous sulphuric acid. The slopes of such plots for p-xylene and mesitylene have values of ∼2.0 whereas for benzene, toluene, and aromatic quaternary ammonium ions, the slopes have values closer to 3.0. The conclusion is drawn that with p-xylene and mesitylene the nitration is diffusion-controlled, but not so with the others.The nitration activation energy, E, varies with both substrate and acid composition. At a given acid composition Ebenzene > Etoluene > Ep-xylene > Emesitylene. As in aqueous sulphuric acid, E, for a given aromatic decreases as the acid concentration is increased. The relative rates of nitration (benzene:toluene: p-xylene: mesitylene) at ∼30 mol % HNO3 and 25 °C are found to be 1:22:256:485. The relative rates, however, are not constant. They narrow as the temperature or acid concentration is raised. Finally it has been shown that the similarity between nitration in aqueous nitric acid and that in aqueous sulphuric acid extends to the reaction between nitronium ion and water. In both media this appears to involve two water molecules and not just one.

Kinetics of the ionization of monoalkylbenzenes and nitroalkanes in polar solvents. 2. Calculation of the outer-sphere reorganization energy

The outer-sphere reorganization energies have been calculated for the ionization of toluene (167 kJ/mole) and cumene (146 kJ/mole) in solutions of potassium tert-butoxide in DMSO.

Kinetics of the ionization of monoalkylbenzenes and nitroalkanes in polar solvents. 3. Calculation of the kinetic parameters of the ionization of toluene and cumene in a solution of potassium tert-butoxide in dimethyl sulfoxide

1. The energies for the reorganization of the structures of the anionic fragments of toluene (∼0) and cumene (∼ 102.5 kJ/mole) and the activation energies for the ionization of these CH acids (74.0 and 85.7 kJ/mole, respectively) in a solution of potassium tert-butoxide in dimethyl sulfoxide have been calculated on the basis of the model developed. 2. The effective distances for the transfer of a proton (0.37 A) and a triton (0.25 A) in the reactions indicated have been found. It has been shown that the values of the kinetic isotope effects in these reactions are mainly determined by the difference between the energies of the intermolecular interaction of the reactants for the transfer of a proton and a triton. 3. An interpretation of the anomalous values of the Bronsted coefficient α (α < 0) for the ionization reactions of monoalkylbenzenes has been given.

Aromatic nitration in aqueous nitric acid

The rates of nitration of benzene, toluene, p-xylene, and mesitylene have been determined in aqueous nitric acid at concentrations between 24–41 mol % HNO3 and at temperatures between 293–333 K. Plots of log10(k1/aHNO3)versus–H0, where k1 is the pseudo-first-order rate constant, aHNO3the activity of the nitric acid, and H0 the Hammett acidity function, are linear, and confirm that the mechanism of nitration in aqueous nitric acid is similar to that in aqueous sulphuric acid. The slopes of such plots for p-xylene and mesitylene have values of ∼2.0 whereas for benzene, toluene, and aromatic quaternary ammonium ions, the slopes have values closer to 3.0. The conclusion is drawn that with p-xylene and mesitylene the nitration is diffusion-controlled, but not so with the others.The nitration activation energy, E, varies with both substrate and acid composition. At a given acid composition Ebenzene > Etoluene > Ep-xylene > Emesitylene. As in aqueous sulphuric acid, E, for a given aromatic decreases as the acid concentration is increased. The relative rates of nitration (benzene:toluene: p-xylene: mesitylene) at ∼30 mol % HNO3 and 25 °C are found to be 1:22:256:485. The relative rates, however, are not constant. They narrow as the temperature or acid concentration is raised. Finally it has been shown that the similarity between nitration in aqueous nitric acid and that in aqueous sulphuric acid extends to the reaction between nitronium ion and water. In both media this appears to involve two water molecules and not just one.

Excited states and electronic spectra of monosubstituted benzenes. An AM1 study

Excited singlet and triplet states of fluorobenzene, aniline, nitrobenzene, toluene, phenol, and phenoxide ion have been calculated using the AM1 semi-empirical method. Electronic transitions have been predicted and compared with experimental values when available.

Multiphoton dissociative ionization of molecules and laser photolysis of molecular toluene ions

An investigation was made of collisionless multiphoton dissociative ionization of gaseous toluene molecules exposed to fourth-harmonic radiation (λ = 266 nm) from a pulsed YAG:Nd3+ laser. The degree of nonlinearity of the processes involving the formation of molecular and fragment ions with masses of 92,91,65, and 39 was found. Secondary photolysis was used to determine the cross sections for the photodissociation of molecular toluene ions at the 266 and 532 nm wavelengths. These were (5 ± 1)× 10−18 and (1.2 ± 0.3)×10−19 cm2, respectively.

Isomeric fluorobenzyl and fluorotropylium cations

The tendency for isomerization of toluene and cycloheptatriene molecular ions, and of benzyl and tropylium product ions, is substantially reduced by fluorine substitution, irrespective of position. This stabilization appears to be due to back-donation of electrons from fluorine, despite its high electronegativity.

The activation energy of the skeletal isomerization in the radical cations of toluene and cycloheptatriene by mass spectrometry of their 2‐phenylethyl derivatives

AbstractThe Unimolecular mass spectrometric fragmentations of the molecular ions of 1,3‐diphenylpropane, 1‐(7‐cycloheptatrienyl)‐2‐phenylethane and the 1‐phenyl‐2‐tolylethanes and their [d5]phenyl analogues have been investigated by metastable ion techniques and measurements of ionization and appearance energies. By comparing the formation of [C7H7]+, [C7H8]+⋅, [C8H8]+⋅ and [C8H9]+ it is shown that the molecular ions of the four diaryl isomers do not undergo ring expansion reactions of the aromatic nuclei prior to these fragmentations. Conversely, the molecular ions of the cycloheptatrienyl isomer suffer in part a contraction of the 7‐membered ring. From these results and from the measured ionization and appearance energies lower limits to the activation energies of these skeletal isomerizations have been estimated yielding E &gt; 33±5 kcal mol−1 formonoalkylbenzene, E &gt; 20 2±5 kc mol−1 for 7‐alkylcycloheptatriene and E &gt; 40±5 kcal mol−1 for dialkylvbenzene positive radical ions. Upper limits can be deduced from literature evidence yielding E &lt; 45 kcal mol−1 for monoalkylbenzene and E &lt; 53 kcal 4mol−1 for dialkylbenzene positive radical ions. The activation energy thus estimated for monoalkylbenzene is in excellent agreement with the recently calculated value(s) for the toluene ion.

Characteristics of a volcano field ion quadrupole mass spectrometer

A field ionization source shaped in the form of a microscopic volcano is coupled with a quadrupole mass spectrometer, and the performance characteristics of the system are measured. The volcano source structure, consisting of a 20-μm diameter rim where field ionization occurs and a 10-μm diameter throat for the passage of sample material, permits the use of high pressure sample gases and yields high efficiency ionization with excellent ion beam optics. Both water and toluene are used as sample gases at source pressures ranging up to the room temperature vapor pressures of these materials (20 torr and 30 torr for water and toluene respectively), and 1-butene has been used up to pressures of 140 torr. The characteristic large background signal produced at low masses when the field ion source is positioned at the entrance of the quadrupole is shown to be due to high energy electrons produced by positive ions colliding with the field ion source structure. This background is effectively eliminated, without offsetting the field ion source from the quadrupole center line, by the use of magnetic and ion optical techniques. Energy analyses are performed on H 3O +, C 4H 5 + (1-butene) and C 6H 5CH 3 + (toluene) ion species by the retarding potential method. The energy full-width at half-height of these species is measured at about 1.9, 1.8 and 1.9 eV respectively.

Comments concerning the structures and reactions of C7H+8 ions

Toluene ions do not abstract NO2 from alkyl nitrates, as has been reported. Rather, solvated NO+2 ions formed in alkyl nitrates transfer NO+2 to aromatic compounds, accounting for the formation of the C7H8NO+2 product ions in toluene-alkyl nitrate mixtures. Information about the structures of fragment C7H+8 ions in butyl benzenes has been derived from the rates of their charge transfer reactions.

Gaseous ions. 2. MINDO/3 study of the rearrangements of toluene and cycloheptatriene molecular ions and the formation of tropylium

Gaseous ions. 2. MINDO/3 study of the rearrangements of toluene and cycloheptatriene molecular ions and the formation of tropylium

Formation of excited singlet toluene in the radiolysis of alkane containing toluene in the solid phase at 77 K

When alkane containing a small amount of toluene is irradiated by γ-ray or X-ray in the solid state at 77 K, luminescence from excited toluene is observed. The formation of the excited toluene is not due to direct excitation of toluene by γ-ray or Čerenkov light, but to the rapid energy transfer from the irradiated alkane to toluene. The intensity of luminescence from the excited toluene in the cyclopentane matrix does not correspond at all to the amounts of toluene ions, which are formed by pre-irradiation. The energy transfer is not caused by a free hole and an electron, but by an exciton. Furthermore, the effect of additives on the fluorescence suggests that the Wannier exciton or mobile ion-pair is responsible for the energy transfer in cyclopentane containing toluene in the solid phase at 77 K.

Unimolecular fragmentation of toluene ions near threshold

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Time-resolved photoionization mass spectrometry. Unimolecular fragmentation of toluene ions near threshold.

A new technique, time resolved photoionization mass spectrometry, allows direct observation of the fragmentation of excited ions. The loss of a hydrogen atom from toluene ions is studied using photoionization wavelengths from 1053 to 1026 Å. Nonlinear least-squares fitting of the decay curves of the molecular ion show that only three discrete states are involved in the fragmentation. One state has a fragmentation rate which is fast (k≫2×104 s−1) on the time scale of the experiment while the other two have rates of 1.3±0.4 and 1.9±0.4 s−1. The present results are consistent with earlier electron impact studies. A careful analysis of previous metastable ion lifetime measurements shows that they do not constitute evidence for a continuous distribution of lifetimes as had earlier been claimed. Evidence presently available indicates that the internal energy distribution of ions formed by electron or photon impact is best described in terms of a relatively small number of discrete states rather than a continuous distribution.

Hidden Rearrangements in the Mass Spectral Decomposition of Cycloheptatriene

Observations concerning the mass spectral decompositions of the toluene and cycloheptatriene molecular ions are reviewed. A mechanism is proposed which explains in a unified manner the apparently conflicting and unresolved isotopic scrambling results. QET calculations supporting this mechanism are presented.

Oxidation of Toluene by Cobalt(III)-Ligand Effects

Cobaltic carboxylates oxidize toluene via a reversible one electron transfer process in acetic acid solution in the absence of oxygen. Lingands of cobaltic ion were found to have a very important role in the oxidation reaction. So we investigated the effect of ligands of cobaltic io n. NeutraI Iigands affectedonIy the activity Co(III)but anion ligands affected both reaction rates and reaction products. Strongly coordinated neutral ligands such as bipyridyl, pyridine or acetonitrile reduced the reduction rate of Co(III)(Table 1, Fig.6). Large anion ligands such as iso-butyric or pelargonic anion suppressed the oxidation by the reversible one electron transfer and were favourable to decarboxylation (Table 4).Accordingly, the effect of ligands on the aromatic oxydation by Co(III)can be attributed to the steric factor rather than to the redox factor, and the rate determing step may be inner sphere complex fermation between toluene and cobaltic ion in one electron transfer process,

Metastable ion characteristics. XVII. Unimolecular decomposition of toluene and cycloheptatriene molecular ions. Variation of the degree of scrambling and isotope effect with internal energy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMetastable ion characteristics. XVII. Unimolecular decomposition of toluene and cycloheptatriene molecular ions. Variation of the degree of scrambling and isotope effect with internal energyFred W. McLafferty and Ian HoweCite this: J. Am. Chem. Soc. 1971, 93, 1, 99–105Publication Date (Print):January 1, 1971Publication History Published online1 May 2002Published inissue 1 January 1971https://doi.org/10.1021/ja00730a019RIGHTS & PERMISSIONSArticle Views92Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (791 KB) Get e-Alerts Get e-Alerts

The ‘preference factor’ and isotope effect in the loss of hydrogen or deuterium from labeled toluenes

AbstractMetastable ion decompositions involving the loss of hydrogen and deuterium from partially deuterated toluene ions were studied using a double focusing mass spectrometer. The electric sector voltage was adjusted so that the only ions transmitted were those which lost a particular fraction of their kinetic energy in decompositions taking place in front of the electric sector. Transitions involving loss of mass 1 or mass 2 from the molecular ions of toluene‐α‐d3 and toluene‐2,3,4,5,6‐d5 were studied. The results showed that in these slow reactions, the ‘preference factor’ defined as the ratio of the probability of loss of a hydrogen atom from a side‐chain position to loss of a hydrogen atom from a ring position was 1.00. The ‘isotope factor,’ defined as the ratio of the probability of loss of a hydrogen atom from any position to that for the loss of a deuterium atom from the same position was found to be 3·50.