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Upstream product

• 100-42-5 styrene 
• 17333-73-2 phenylium 
• 106-95-6 allyl bromide 
• 475503-68-5 Ethylidene-oxonium 
• 71-43-2 benzene 
• 463-49-0 1,2-propanediene 
• 1165952-92-0 cyclohexa-1,4-diene 
• 1165952-91-9 cyclohexa-1,3-diene 
• 71-43-2 benzene radical cation 

Downstream Products

• 53807-53-7 C₆H₆F⁽¹⁺⁾ 
• 71-43-2 benzene 
• 475503-68-5 Ethylidene-oxonium 
• 71-43-2 benzene radical cation 
• 74-86-2 acetylene 
• 17333-73-2 phenylium 
• 17836-08-7 methoxonium ion 

Relevant academic research and scientific papers

Elemental Compositions from Daughter Ion Spectra of m1+ and 1 + 1>+: Some Applications of the Method

The elemental compositions of ions can be determined in tandem mass spectrometry by comparing the daughter ion spectra of the m1+ and 1 + 1>+ ions.The method is demonstrated for mass-analyzed ion kinetic energy spectra but is applicable to all types of daughter ion spectra, including complex collisionally activated dissociation spectra.In this work, the method is applied to compounds that produce daughter ions of known elemental compositions, and the errors and limitations are evaluated.Following that test, the procedure is applied to a compound that may produce daughters of more than one possible elemental composition.The method is sometimes useful even if the formula of the parent is not known; that is, the formulae of unknown parent and daughter ions may be found.Locating a specific atom in an isotopically labeled molecule is another capability of the method.The basic equation of the method was generalized and incorporated into a computer program for performing the calculations.

Evaluation of Superacid Strength from the Protonation of Benzene. Comparison of HF-SbF5, HF-TaF5, and HBr-AlBr3 Systems

The degree of protonation of benzene in HF-SbF5, HF-TaF5, and HBr-AlBr3 solutions has been investigated by carbon-13 NMR spectroscopy.Both 30:1 HF-SbF5 and HBr-AlBr3 are much stronger acids than 30:1 HF-TaF5 (55percent protonation at a TaF5/benzene ratio of 3) or 4:1 HF-TaF5 (68percent protonation at a TaF5/benzene ratio of 2.5).HBr-AlBr3 protonates benzene completely down to a AlBr3/benzene ratio of 2.Under HBr pressure, 3.5-4 mol of HBr for each mole of AlBr3 are taken into the benzenium bromoaluminate solution.The "sludge" catalysts commonly encountered in hydrocarbon conversions are actually solutions of carbocations in the HBr-AlBr3 superacid.The high acidity revealed by the benzene protonation is representative for such sludges.The acidity measurement by benzene protonation can in principle be extended to other superacid systems.

H-D Exchange at Low Energy in a Collision Cell Between Protonated Aromatic Hydrocarbons and D2O, CD3OD and C6D6

H-D exchange reactions which occur between protonated molecules (mainly aromatic hydrocarbons) and deuterated neutrals (D2O, CD3OD and benzene-d6) were studied using a hexapole collision cell.The efficiency of exchange is dependent on the proton affinity difference between aromatic and target molecules but the pattern of deuteration in the exchanged ions does not change as might be expected with collision gas pressure.The incident ion energy also has only a small effect on the pattern up to a certain value, but above that value no exchange occurs.It is suggested that ions which show multiple exchange have the same distribution of transit times, independent of collision gas pressure and, within the above limits, of initial energy.The rate-determining step is then exchange in an ion-molecule complex rather than collision rate.

Electronic transitions of protonated benzene and fulvene, and of C 6H7 isomers in neon matrices

Electronic transitions of protonated benzene (A 1B 2X 1A1, origin at 325 nm) and ±-protonated fulvene (A 1A′X 1A′, at 335 nm) trapped in 6 K neon matrices have been detected. The cations were produced from several different precursors, mass-selected, and co-deposited with neon. After neutralization of the cations, the electronic transitions of cyclohexadienyl (onsets at 549 and 310 nm) and ±-hydrogenated fulvene (532 and 326 nm) radicals were identified. Upon excitation of cyclohexadienyl to the B 2B1 state, photoisomerization to an open-chain structure and ±-hydrogenated fulvene was observed.

Dissociative proton transfer reactions of H3+, N2H+, and H3O+ with acyclic, cyclic, and aromatic hydrocarbons and nitrogen compounds, and astrochemical implications

A flowing afterglow-selected ion flow drift tube has been used to measure the rate coefficients and product ion distributions for reactions of H3O+, N2H+, and H3+ with a series of 16 alkanes, alkenes, alkynes, and aromatic hydrocarbons as well as acrylonitrile, pyrrole, and pyridine. Exothermic proton transfer generally occurs close to the collision rate. The reactions of H3O+ are mostly nondissociative and those of H3+ are mostly dissociative, but many reactions, especially those of N2H+, have both dissociative and nondissociative channels. The dissociative channels result mostly in H2 and/or CH4 loss in the small hydrocarbons and in toluene, loss of C2H2 from acrylonitrile, and loss of HCN from pyrrole. Only nondissociative proton transfer is observed with benzene, pyridine, and larger aromatics. Drift tube studies of N2H+ reactions with propene and propyne showed that increased energy in the reactant ion enhances fragmentation. Some D3+ reactions were also investigated and the results suggest that reactions of H3+ with unsaturated hydrocarbons B proceed through proton transfer that forms excited (BH+)* intermediates. Pressure effects suggest that a fraction of the (BH+)* intermediates decomposes too rapidly to allow collisional stabilization in the flow tube (t -8 s). The other low-energy (BH+)* intermediates are formed by the removal of up to 40% of the reaction exothermicity as translational energy, and these intermediates result in stable BH+ products. The results suggest that, in hydrogen-dominated planetary and interstellar environments, the reactions of H3+ can convert C2-C6 hydrocarbons to smaller and less saturated molecules, but polycyclic aromatics are stable against decomposition by this mechanism. The dissociative reactions of H3+ can therefore favor the accumulation of small unsaturated hydrocarbons and aromatics in astrochemical environments.

Combined experimental and theoretical study of the protonation of polyfluorobenzenes [C6H(6-n)F(n)] (n = 0-6)

In a recent high-pressure mass spectrometric revision to the gas-phase basicity scale (J. E. Szulejko and T. B. McMahon, J. Am. Chem. Sec. 115, 7839 (1993)), it was observed that the proton affinity for hexafluorobenzene was 24 kcal mol-1 (1 kcal = 4.184 kJ) lower than the accepted National Institute of Science and Technology (NIST) database value of 177.7 kcal mol-1 (S. G. Lias et al., J. Phys. Chem. Ref. Data 17, Suppl. 1 (1988)). Furthermore, the proton affinities for most other polyfluorobenzenes were also found to differ substantially from the NIST values. For many of the polyfluorobenzenes large protonation entropy changes were noted, which were substantially greater than then those expected from rotational symmetry number changes alone. In view of these observations, MP2/6-31G**/HF/6-31G** ab initio calculations were undertaken to investigate further the proton affinity and entropy changes with respect to the degree of fluorine substitution. The present proton affinity variations found for the polyfluorobenzenes (hexaflorobenzene excepted) can be interpreted with the aid of the ab initio results in terms of a simple additivity scheme. Each fluorine substituent para, meta, ortho or ipso to the ring protonation site will induce an incremental proton affinity change with respect to benzene of 1.5, -7.0, -1.5 and -19.0 kcal mol-1, respectively. This additivity scheme can also be used to rationalize the re-evaluated proton affinities for the polymethylbenzenes and m- and o-fluorotoluenes. The corresponding methyl increments are 7.5, 5.5, 2.5 and 1.0 kcal mol-l for para, meta, ortho and ipso protonation respectively. From the present ab initio statistical thermodynamic analysis of the various protonation entropy components, it was concluded that the low frequency vibrations are almost exclusively responsible for the large excess entropy changes observed experimentally. Ab initio calculated barriers for 1,2 proton shifts in arenium species available in the literature are concluded to be too large to allow the existence of a so-called dynamic proton. Large excess protonation entropies are noted from the literature for polymethylbenzenes, naphthalene and 1-methylnaphthalene.

Reactions of Hydrated Hydronium Ions and Hydrated Hydroxide Ions with Some Hydrocarbons and Oxygen-Bearing Organic Molecules

The rate coefficients and ion products have been determined at 300 K for the reactions of H3O(1+)*(H2O)0,1,2,3 positive ions and OH(1-)*(H2O)0,1,2 negative ions with six hydrocarbons and six oxygen-containing organic species using a selected ion flow tube (SIFT) for the positive ions and a flowing afterglow (FA) for the negative ions.This study was initiated in support of a major development program of the SIFT and FA as chemical ionization devices for the analysis of trace gases in air and especially of human breath and the vapors emitted by fruits and food products.The H3O(1+) and OH(1-) ions mostly react with the molecules, MH, via proton transfer, producing respectively MH2(1+) and M(1-) ions, which is ideal for gas analysis.The hydrated hydronium ions and the hydrated hydroxide ions are largely unreactive with the hydrocarbons included in this study, but they are very reactive with the oxygen-containing organic molecules undergoing ligand switching reactions producing mostly MH2(1+) and M(1-) hydrates.The details of the reactions (e.g. the number of H2O molecules either ejected from the intermediate complexes or remaining associated with the MH2(1+) and MH(1-) "core ions") are controlled largely by the reaction energy as far as this can be determined.The utility of the reactions of these hydrated ions as chemical ionization agents in atmospheric trace gas analysis is alluded to.Additionally, new FA data on the three-body association reactions of OH(1-) and OH(1-)*H2O with CO2 are presented.

Structures of Product Ions C6H7(+) and C6H9(+) of Ion-Molecule Reactions with Allyl Bromide

The ion-molecule reactions of allyl bromide with the molecular ion of allyl bromide and with its major fragment, the allyl ion, yield the C6H7(+) and C6H9(+) ions.The structure of these product ions was explored by means of photofragmentation with laser light in the 10 μm region and by proton transfer reaction to selected reagents.These product ions were also formed by other reactions and their reactivities compared.In both cases the presence of at least two populations is demonstrated.For C6H9(+) these two populations are initially present, whereas for C6H7(+) an isomer is formed by the infrared light before the loss of H2.When this ion is produced by photofragmentation of C6H9(+), at least one third, stable isomer is formed.Two isomers of C6H5(+) are formed in the photofragmentation of C6H7(+), but only one form photofragments further by loss of C2H2.The use of non-linear least-squares fitting does not allow definite conclusions to be drawn concerning the kinetics of the consecutive photofragmentations.

Thermodynamic Studies of Gas-phase Proton Transfer Equilibria involving Benzene: A Reassessment of Earlier Data

Temperature-variable equilibrium constant measurements have been performed for a number of proton-transfer equilibria in which benzene was a partner, using a newly built high-pressure pulsed source mass spectometer.Entropy values obtained showed that the protons in protonated benzene are not as mobile as previously thought.Systems involving ethanol are found to give anomalous, though self-consistent results owing to the onset of thermal decomposition.In the light of this, previous data involving halotoluenes and xylenes which appear to show unusually large increases in entropy on protonation, have been reassessed.There is evidence of proton-induced isomerisation.In the reaction H(1+) -> H(1+) the free energy of activation is derived to be ca. 90 kJ mol-1 from a computer model fit to the results, consistent with the energy calculated to be needed for a proton shift from the 3 to the 4 position in the precursor.The equivalent reaction for protonated 4-fluorotoluene has a barrier which is ca. 10 kJ mol-1 higher.A kinetic scheme is presented which shows how this could account for the observed 'thermodymanimc' behaviour, and also give rise to the 'isokinetic effects' previously noted.There has therefore been some readjustment of the recommended proton affinity values for some of these compounds.

Gas-phase measurements of the kinetics of BF2(+)-induced polymerization of olefinic monomers

The initial steps in the BF2(+)-induced polymerization of the monomers of ethylene, propylene, cis-2-butene, isobutene, and styrene have been observed in the gas phase at room temperature using the Selected-Ion Flow Tube (SIFT) technique.Rate constants and product distributions have been determined for the initiation of the polymerization in each case.All five initiation reactions were found to be rapid (k >/= 5.0*10-10 cm3 molecule-1 s-1).The primary product ions that propagate polymerization have been identified and sequential addition reactions have been followed in all five systems.For ethylene the energetics of the initial steps have been followed using ab initio molecular orbital theory.Reaction of BF2+ with the vapours of water and benzene have also been characterized. Key words: ion-induced polymerization; alkenes; kinetics; gas phase ion chemistry