Picosecond ultraviolet multiphoton laser photolysis studies of photoionization phenomena in neat liquids and nonpolar solutions

Mechanisms of photoionization and cation-anion or cation-electron recombination processes leading to the formation of excited states or chemical reactions have been discussed on the basis of the results of picosecond u.v. multiphoton laser photolysis and time resolved transient spectral studies of nonpolar, as well as slightly polar, neat liquids such as saturated hydrocarbons and benzenes, and have been compared with the case of pulse radiolysis studies. Moreover, similar problems have also been discussed on the basis of the results of picosecond u.v. multiphoton laser photolysis studies of some nonpolar solutions containing aromatic solutes.     

Hydroxylation of selected hydrocarbon ions on reaction with methanol in the gas phase

The ion-molecule reactions of selected hydrocarbon cations with methanol which lead to the production of hydroxylated odd-electron molecular ions in the high-pressure ion source of a mass spectrometer or in the central quadrupole of a tandem quadrupole mass spectrometer are described. A wide variety of hydrocarbon cations were investigated, including aliphatic and aromatic cations; of these, only those having a vacant site on an aromatic system appear to undergo the hydroxylation reaction in high yield. A mechanism is proposed for the formation of the molecular ion of phenol from the ion-molecule reaction involving the phenyl cation with methanol. In addition, thermochemical data are provided which support the formation of the postulated species.     

芳烃酰基化后还原制备芳香醇的工艺进展

芳烃制备高附加值精细化学品芳香醇(9-芴甲醇),一直以来存在产物选择性低以及合成成本高等问题。基于此,本文主要综述了芳烃酰基化后还原合成芳香醇的工艺,包括第一步采用Friedel-Crafts酰基化反应、Vilsmeier-Haack反应、Reimer-Tiemann反应、Duff反应等过程将芳烃酰基化合成芳香醛/酮;第二步通过金属氢化物还原、催化加氢还原、活泼金属还原、Cannizarro反应、Meerwein-Ponndorf-Verley还原反应等过程将芳香醛/酮还原合成芳香醇。在总结和归纳各种工艺过程优缺点的基础上,提出了合理的芳香醇制备工艺,为9-芴甲醇产业化制备技术的开发提供帮助。     

Carbon-carbon bond cleavage in the photoionization of ethanol and 1-propanol clusters

Tunable VUV laser was used to initiate the ion-molecule reactions in the clusters of ethanol and 1-propanol by photoionization in the region between 10.49 to 10.08 eV. Ionic products were detected by the time-of-flight mass spectrometer. In addition to the protonated clusters from proton transfer reactions, the products corresponding to beta carbon-carbon bond cleavage were found to be one of the major products for small sizes of clusters. A comparison with photoionization of methanol clusters and the results of ab initio calculation has been made.     

Solid state radiation chemistry—features important in basic research and applications

Solid state radiation chemistry is briefly reviewed with attention to some important features that distinguish it from liquid state radiation chemistry: (i) reactions of primary products of radiolysis in the solid state can proceed via a path different than that of the same material in liquid phase (example: very slow reaction of dry electron with N₂O); (ii) “molecular products” of radiolysis appear in any aqueous system, also in the solid state due to the always identical physical mechanism of heterogenous energy deposition; (iii) there are basic differences in transportation of products of radiolysis, transient and stable, in solid matrices (example: CH₃C√HCO⁻₂ decay in liquid and solid state); (iv) specific behaviour of systems of high macro- but low micro-viscosity (example: gels); (v), independence of radiolysis products formation in single and multi-ionization spurs, especially at higher LET values (example: crystalline alanine); (vi) quantitative determination of the yield of multi-ionization spurs in alanine during low LET irradiation shows similar participation of single- and multi-ionization spurs as in water.     

Two-Photon Photochemical Reactions of Aromatic Compounds in the Gas Phase

Studies on the gas-phase two-photon photochemistry of aromatic compounds performed in the past 25 years were summarized. Photophysical and photochemical unimolecular and bimolecular reactions occurring in the gas phase on the exposure of molecular systems (aliphatic aldehydes, ketones, and alcohols; aromatic hydrocarbons and their halogen derivatives; and heteroaromatic compounds with a conjugated -electron system) to pulsed laser UV radiation were considered. Data on the kinetics and mechanisms of primary two-photon photoexcitation, photodissociation, and photoionization of aromatic molecules were systematized, and the nature of electronically excited states responsible for these processes was determined. Data on the reactivity of transient species and on the kinetics of elementary steps of laser UV photolysis (bimolecular charge transfer and heavy particle transfer reactions and termolecular association and cluster ion formation reactions) were presented. General prerequisites to the stability of aromatic compounds under non-steady-state conditions of UV photolysis were found in accordance with the electronic structure of reactants and with the donor–acceptor properties of mixture components.     

氯苯类污染物在高层大气环境中形成的可能性

简要地总结了大气离子与自由基反应的研究进展和以氯苯为目标产物的气相离子-分子反应的质谱研究。根据大气层状结构图、高层大气的特点以及相关的研究结果,提出了氯苯类污染物的形成不排除是大气化学反应尤其是离子反应产物的观点。对进一步研究大气中氯苯类污染物的生成机制和控制具有重要意义。     

APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds

The technique of atmospheric pressure photoionization (APPI) has several advantages over electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), including efficient ionization of nonpolar or low charge affinity compounds, reduced susceptibility to ion suppression, high sensitivity, and large linear dynamic range. These benefits are greatest at low flow rates (i.e., 相似文献   

Negative ions generated by reactions with oxygen in the chemical ionization source. I. Characterization of gas-phase and wall-catalyzed reactions of fluorene,anthracene and fluoranthene

The methane negative ion chemical ionization (NICI) mass spectra of polycyclic aromatic hydrocarbons are usually dominated by molecular, M^{? ˙} or M ? H^? ions; however, ions resulting from additions to M have also been reported. Some of these ions have been observed at [M + 14]^{? ˙}, [M + 15]^?, [M + 30]^? and [M + 32]^?˙ and have been attributed to reactions with either oxygen-containing impurities in the buffer gas or alkyl radical species generated by ionization of a hydrocarbon buffer gas. In this study, the NICI spectra of fluorene, anthracene and fluoranthene were studied in detail using quadrupole and Fourier transform mass spectrometers. Spectra were acquired when reactive species such as oxygen, water, nitrous oxide and carbon dioxide were added to the nitrogen buffer gas. Experiments with deuterated methane were also carried out. These studies indicated that buffer gas impurities affect the NICI spectra; however, gas-phase ion-molecule reactions were not responsible for all of the observed products. In addition to electron- and ion-molecule reactions, ions were observed that resulted from wall-catalyzed oxidation reactions followed by electron capture. These reactions were enhanced by the addition of oxygen and elevated ion source temperatures. Depending upon the parent PAH structure, oxidation products such as ketones, quinones and anhydrides were formed.     

Oxygen effect on the photoisomerization and photoionization of fumaronitrile through its exciplexes

The photoisomerization and photoionization reactions of fumaronitrile through its exciplexes with some aromatic electron donors has been studied with the aid of nanosecond laser photolysis and gas chromatography. The rate of the transcis isomerization reaction is found to be strongly enhanced by dissolved oxygen. The mechanism of the reaction is analysed quantitatively in terms of oxygen enhanced single—triplet intersystem crossing.     

Anion radicals and dianions as electron transfer reagents

The catalytic regeneration of depolarizers by certain substrates has been demonstrated by means of cyclic voltammetry. As depolarizers we have employed anion radicals of aromatic hydrocarbons, heteroaromatic compounds, ketones, esters, nitriles, and olefins, and dianions of aromatic hydrocarbons, heteroaromatic compounds, ketones, and esters. As substrates we have investigated simple aromatic and aliphatic halides, 1,2- and 1,3-dihalides, carbon dioxide, and activated olefins. A requirement for the observation of a catalytic wave is that the reduced substrate undergoes a practically irreversible reaction after the reaction with the reduced depolarizer; for simple halides it is a cleavage reaction, for 1,2- and 1,3-dihalides an elimination, for carbon dioxide an addition, and for activated olefins a coupling. Electrochemical investigations of these kinds of reactions may be of interest in connection with the mechanism of several types of reactions in organic chemistry.     

The study of state-selected ion-molecule reactions using the vacuum ultraviolet pulsed field ionization-photoion technique

This paper presents the methodology to generate beams of ions in single quantum states for bimolecular ion-molecule reaction dynamics studies using pulsed field ionization (PFI) of atoms or molecules in high-n Rydberg states produced by vacuum ultraviolet (VUV) synchrotron or laser photoexcitation. Employing the pseudocontinuum high-resolution VUV synchrotron radiation at the Advanced Light Source as the photoionization source, PFI photoions (PFI-PIs) in selected rovibrational states have been generated for ion-molecule reaction studies using a fast-ion gate to pass the PFI-PIs at a fixed delay with respect to the detection of the PFI photoelectrons (PFI-PEs). The fast ion gate provided by a novel interleaved comb wire gate lens is the key for achieving the optimal signal-to-noise ratio in state-selected ion-molecule collision studies using the VUV synchrotron based PFI-PE secondary ion coincidence (PFI-PESICO) method. The most recent development of the VUV laser PFI-PI scheme for state-selected ion-molecule collision studies is also described. Absolute integral cross sections for state-selected H2+ ions ranging from v+ = 0 to 17 in collisions with Ar, Ne, and He at controlled translational energies have been obtained by employing the VUV synchrotron based PFI-PESICO scheme. The comparison between PFI-PESICO cross sections for the H2+(HD+)+Ne and H2+(HD+)+He proton-transfer reactions and theoretical cross sections based on quasiclassical trajectory (QCT) calculations and three-dimensional quantum scattering calculations performed on the most recently available ab initio potential energy surfaces is highlighted. In both reaction systems, quantum scattering resonances enhance the integral cross sections significantly above QCT predictions at low translational and vibrational energies. At higher energies, the agreement between experiment and quasiclassical theory is very good. The profile and magnitude of the kinetic energy dependence of the absolute integral cross sections for the H2+(v+ = 0-2,N+ = 1)+He proton-transfer reaction unambiguously show that the inclusion of Coriolis coupling is important in quantum dynamics scattering calculations of ion-molecule collisions.     

Ion formation mechanisms in UV-MALDI

Matrix Assisted Laser Desorption/Ionization (MALDI) is a very widely used analytical method, but has been developed in a highly empirical manner. Deeper understanding of ionization mechanisms could help to design better methods and improve interpretation of mass spectra. This review summarizes current mechanistic thinking, with emphasis on the most common MALDI variant using ultraviolet laser excitation. A two-step framework is gaining acceptance as a useful model for many MALDI experiments. The steps are primary ionization during or shortly after the laser pulse, followed by secondary reactions in the expanding plume of desorbed material. Primary ionization in UV-MALDI remains somewhat controversial, the two main approaches are the cluster and pooling/photoionization models. Secondary events are less contentious, ion-molecule reaction thermodynamics and kinetics are often invoked, but details differ. To the extent that local thermal equilibrium is approached in the plume, the mass spectra may be straightforwardly interpreted in terms of charge transfer thermodynamics.     

Solid state chemical ionization for characterization of organic compounds by laser mass spectrometry

A new technique involving the addition of a compound to the analyte to serve as a source of "reagent" ions has been developed for negative-ion laser mass spectrometry. This "solid state chemical ionization" leads to ions characteristic of the analyte, owing to ion-molecule reactions between the "reagent" ion and the neutral analyte in the laser-generated plume. Polycyclic aromatic hydrocarbons show formation of an ion corresponding to (M + O - H)(-) in their negative-ion laser mass spectra when mixed with compounds such as sym-trinitrobenzene, sodium nitrate and sodium peroxide. NO(-)(2), O(-), and O(-)(2) serve as "reagent" ions in these compounds. Formation of (M + Cl)(-) is seen in the laser mass spectra of glycosides mixed with hexachlorobenzene. Chloride serves as the "reagent" ion in this case.     

Fullerene-like chemistry at the interior carbon atoms of an alkene-centered C26H12 geodesic polyarene

The title compound (1) undergoes 1,2-addition reactions of both electrophilic and nucleophilic reagents preferentially at the "interior" carbon atoms of the central 6:6-bond to give fullerene-type adducts 2, 3, 4, and 5. Such fullerene-like chemistry is unprecedented for a topologically 2-dimensional polycyclic aromatic hydrocarbon and qualifies this geodesic polyarene as a "bridge" between the old flat world of polycyclic aromatic hydrocarbons (PAHs) and the new round world of fullerenes. The relief of pyramidalization strain, as in the addition reactions of fullerenes, presumably contributes to the atypical mode of reactivity seen in 1. Molecular orbital calculations, however, reveal features of the nonalternant pi system in 1 that may also play an important role. Thus, the fullerene-like chemistry of 1 may be driven by two or more factors, the relative importances of which are difficult to discern.     

Evidence of neutral radical induced analyte ion transformations in APPI and Near-VUV APLI

We report on the reactions of neutral radical species [OH, Cl, O(³P), H], generated in a typical atmospheric pressure ionization (API) source upon irradiation of the sample gases with either 193 nm laser radiation or 124 nm VUV light, the latter commonly used in atmospheric pressure photoionization (APPI). The present investigations focus on the polycyclic aromatic hydrocarbon pyrene as representative of the aromatic compound class. Experimental results are supported by computational methods: simple kinetic models are used to estimate the temporal evolution of the concentrations of reactants, intermediates, and final products, whereas density functional theory (DFT) energy calculations are carried out to further elucidate the proposed reaction pathways. The neutral radicals are generated upon photolysis of background water and oxygen always present in appreciable mixing ratios in typical API sources. Substantial amounts of oxygenated analyte product ions are observed using both techniques. In contrast, upon atmospheric pressure laser ionization (APLI) with 248 nm radiation, oxygenated products are virtually absent. In addition, kinetic data evaluation yielded a bimolecular rate constant of k=(1.9±0.9)×10⁻⁹ cm³ molecule⁻¹ s⁻¹ for the reaction of the pyrene radical cation with OH radicals.     

Ion-Molekül-Reaktionen und Hammett-Gleichung

In order to determine the relationship between elementary ion-molecule reactions in the gas phase and certain steps of chemical reactions in the liquid phase, we have tried to model the formation of σ-complexes as part of the electrophilic aromatic substitution reaction by means of a proton transfer reaction to aromatic molecules. The Hammett equation should provide the necessary criteria for such a relationship. The comparison of the Hammett σ-constants with the cross section ratios for the proton transfer reaction of unsubstituted and substituted aromatics—the latter being representative of the corresponding reaction rate constants—does not yield a linear relationship and therefore suggests that the Hammett equation is not valid in the domain of gas phase reactions. If, on the other hand, the σ-constants are set in relation with the proton affinity PA, i.e. with the energy released during the formation of a σ-complex, a linear or otherwise well-defined relationship results. This observation was taken to be an indication of the fact that the Hammett equation is also valid in the case of ion-molecule reactions.     

Gas-phase reactions of aryl radicals with 2-butyne: experimental and theoretical investigation employing the N-methyl-pyridinium-4-yl radical cation

Aromatic radicals form in a variety of reacting gas-phase systems, where their molecular weight growth reactions with unsaturated hydrocarbons are of considerable importance. We have investigated the ion-molecule reaction of the aromatic distonic N-methyl-pyridinium-4-yl (NMP) radical cation with 2-butyne (CH(3)C≡CCH(3)) using ion trap mass spectrometry. Comparison is made to high-level ab initio energy surfaces for the reaction of NMP and for the neutral phenyl radical system. The NMP radical cation reacts rapidly with 2-butyne at ambient temperature, due to the apparent absence of any barrier. The activated vinyl radical adduct predominantly dissociates via loss of a H atom, with lesser amounts of CH(3) loss. High-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry allows us to identify small quantities of the collisionally deactivated reaction adduct. Statistical reaction rate theory calculations (master equation/RRKM theory) on the NMP+2-butyne system support our experimental findings, and indicate a mechanism that predominantly involves an allylic resonance-stabilized radical formed via H atom shuttling between the aromatic ring and the C(4) side-chain, followed by cyclization and/or low-energy H atom β-scission reactions. A similar mechanism is demonstrated for the neutral phenyl radical (Ph˙)+2-butyne reaction, forming products that include 3-methylindene. The collisionally deactivated reaction adduct is predicted to be quenched in the form of a resonance-stabilized methylphenylallyl radical. Experiments using a 2,5-dichloro substituted methyl-pyridiniumyl radical cation revealed that in this case CH(3) loss from the 2-butyne adduct is favoured over H atom loss, verifying the key role of ortho H atoms, and the shuttling mechanism, in the reactions of aromatic radicals with alkynes. As well as being useful phenyl radical analogues, pyridiniumyl radical cations may form in the ionosphere of Titan, where they could undergo rapid molecular weight growth reactions to yield polycyclic aromatic nitrogen hydrocarbons (PANHs).     

高中生“芳香烃”心智模型的测评及其教学启示*

采用二阶式纸笔测验以及半结构化访谈法对高中生持有的“芳香烃”心智模型进行测评,并重点分析了学生建构的与“芳香烃和苯的同系物的概念”“芳香烃的结构”“苯及其同系物的化学性质”等概念群相关的缺陷模型。研究发现学生建构的有关“芳香烃”缺陷模型包括3大类共计11种;学生对有机物空间结构的想象力和建构能力较为薄弱;学生对“有机化合物结构内基团之间相互作用对其化学性质的影响”认识不足,“性质结构”模型不完善;学生建构的有机化学的心智模型尚不具备整体性。     

Kinetic regularities of the heat release during the reactions of aliphatic hydrocarbons with aqueous HNO3

The kinetics of the heat release during the reactions of aqueous HNO₃ withn-heptane andn-octadecane was studied. The kinetic regularities of the reactions of hydrocarbons C₇H₁₆−C₁₈H₃₈ with HNO₃ and the heats of the reactions were described. At all stages, except initial, the hydrocarbon reacts with NO₂ and nitric acid reproduces NO₂ in the reaction with NO. The accumulation of NO₂ results in the acceleration of the process. When the pressure of the hydrocarbon vapor is equilibrium, its reaction with NO₂ can also proceed in the gas phase. The contribution of this reaction to the total heat release was estimated. The additives of aromatic and unsaturated hydrocarbons to aliphatic hydrocarbons increase strongly the initial rate of the heat release and changes slightly the subsequent stages of the process. Naphthenic hydrocarbons have almost no effect on the kinetic parameters of the process. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–40, January, 1998.