Temperature change of OD ESR and freon matrix ESR of the radical cations of 9,10-octalin and cyclohexene

The optical detection (OD) ESR and Freon matrix ESR spectra were observed for the radical cations of 9,10-octalin and cyclohexene from 77 to 300 K. The observed spectral change was attributed to ring inversion in both radical cations based on MO calculations and an analysis by the modified Bloch equation. The activation energy for the inversion of the radical cation of octalin was calculated as 18.8 kJ mol⁻¹.     

Pulse radiolysis of cyclohexane: The identity of the high-mobility positive ion

Previous experimental observations and new pulse radiolysis results concerning the high-mobility positive ion in cyclohexane are examined. Apparent disagreement among these observations concerning the existence of a high-mobility positive ion can be explained if there are two positive ions of major importance in cyclohexane radiolysis. The possibility is examined that the c-C₆H₁₂⁺ ion has a “normal” mobility and that hydride transfer or proton transfer, involving c-C₆H₁₁⁺ or c-C₆H₁₃⁺ respectively, is responsible for the observed high mobility.     

Isotopic effect in the radiolysis of water. Diffusion-kinetic modelling up to 300°C

Diffusion-kinetic calculations [1-3] have been analysed to determine the isotopic effect in the radiolysis of water with ionising radiation of linear energy transfer characteristics (LET) from 0.2 to 60 eV/nm and at temperatures up to 300°C. This analysis shows that, for low LET radiation, the spur decay of e^- _aq is slower in D₂O and results in a higher yield of e^- _aq, g(e^- _aq), at 10^-7 -10^-6s after the ionisation event. In low LET radiolysis, g(OD) ≈ g(OH) over the whole range of temperature but in high LET radiolysis g(OD) is clearly lower than g(OH). The isotopic effect on the yields of the radical products is enhanced by increasing LET but diminished by increasing temperature. The yields of the molecular products show the opposite isotopic effect to their radical precursors, namely g(D₂) is 10-20% lower than g(H₂) and g(D₂O₂) > g(H₂O₂). A particularly significant difference between g(D₂O₂) and g(H₂O₂) has been found at LET = 20 eV/nm. The isotopic dependence of the g-values estimated for fast neutron radiolysis is also presented.     

The reactions of some interstellar ions with benzene,cyclopropane and cyclohexane

The reactions of the cyclic molecules C₆H₆ (benzene), c-C₃H₆ (cyclopropane) and c-C₆H₁₂ (cyclohexane) with ArH⁺ (ArD⁺), H₃⁺, N₂H⁺, CH₅⁺, HCO⁺, OCSH⁺, C₂H₃⁺, CS₂H⁺ and H₃O⁺ have been studied at 300 K using a SIFT apparatus. All the reactions except those of C₂H₃⁺ proceed via proton transfer and all are fast except the H₃O⁺ and CS₂H⁺ reactions with c-C₆H₁₂ which are endothermic and which establish that the proton affinity of c-C₆H₁₂ is 160 ± 1 kcal mol⁻¹, which is considerably lower than the published value. In the c-C₃H₆ and the c-C₆H₁₂ reactions multiple products are observed and hence “breakdown curves” for the protonated molecules are constructed and the appearance energies of the various ion products are consistent with available thermochemical data. The reactions of C₂H₃⁺ with these cyclic molecules are atypical within this series of reactions in that they appear to proceed largely via hydride ion transfer. The implications of the results of this study to interstellar chemistry are alluded to.     

ESR,XPS, UV-VIS and FT-IR investigations on the interaction of no and O2 with highly dispersed C60 supported on silica,titania and alkali cation-exchanged Y-zeolites

The characteristics of the radical sources in highly dispersed C₆₀ samples supported on silica, titania ad alkali cation-exchanged Y-zeolite were investigated in the presence and absence of NO and O₂by means of ESR, FT-IR and UV-diffuse reflectance spectroscopies, the results of which were compared with those of the bulk C₆₀ sample. In the presence of O₂, C₆₀ dispersed onto supports was found to easily generate ESR signals in ambient conditions or under UV-irradiation. The intensity of the ESR signal of the C₆₀ samples were found to strongly depend on the dispersibility of C₆₀, the kind of support and the degassing temperature. Based on these results, the nature of these ESR active species in C₆₀ was discussed in detail for the first time. The addition of NO led to a dramatic decrease in the intensity of the ESR signal, its extent also strongly depending on the kind of support, i.e., silica or Y-zeolite and the exchanged-alkali cations on zeolite, i.e., H⁺, Na⁺, Cs⁺, while such a decrease was not observed for the bulk C₆₀.     

Heat of formation for the SH radical by photoionization mass spectrometry

Photoionization mass spectrometry has been used to measure the appearance energies for [C₂H₅]⁺ from ethanethiol, [C₃H₇]⁺ from 2-propanethiol and [C₃H₅]⁺ from 2-methylthiirane. From the known thermochemistry of these cations and their precursor molecules, a 298 K heat of formation of 138.6±0.4 kJ mol^?1 for the SH radical has been derived.     

Unimolecular reactions of [C5H10O]+ ˙ radical cations derived from4-penten-1-ol

The reactions of metastable [C₅H₁₀O]^{+ ˙} radical cations produced by ionization of 4-penten-1-ol are reported and discussed. These [C₅H₁₀O]^{+ ˙} species undergo mainly ethyl radical loss, with smaller contributions of methyl radical and water expulsion. ²H-Labelling studies reveal different specificities of hydrogen selection in these three fragmentations. The behaviour of these [C₅H₁₀O]^{+ ˙} ions is compared to those reported previously for isomeric radical cations containing linear alkenyl chains and a terminal hydroxyl group.     

Structures of decomposing and non-decomposing gas-phase [C4H6O]+· radical cations,and their [C2H2O]+· and [C3H6]+· product ions

The structures of gas-phase [C₄H₆O]^+· radical cations and their daughter ions of composition [C₂H₂O]^+· and [C₃H₆]^+· were investigated by using collisionally activated dissociation, metastable ion measurement, kinetic energy release and collisional ionization tandem mass spectrometric techniques. Electron ionization (70 eV) of ethoxyacetylene, methyl vinyl ketone, crotonaldehyde and 1-methoxyallene yields stable [C₄H₆O]^+· ions, whereas the cyclic C₄H₆O compounds undergo ring opening to stable distonic ions. The structures of [C₂H₃O]^+· ions produced by 70-eV ionization of several C₄H₆O compounds are identical with that of the ketene radical cation. The [C₃H₆]^+· ions generated from crotonaldehyde, methacrylaldehyde, and cyclopropanecarboxaldehyde have structures similar to that of the propene radical cations, whereas those ions generated from the remainder of the [C₄H₆O]^+· ions studied here produced a mixed population of cyclopropane and propene radical cations.     

Od ESR spectra of cis-decalin radical cations in liquid and glassy solutions: Evidence of radical cation stabilization in glassy cis-decalin

The resolved optically detected electron spin resonance (OD ESR) spectrum for cis-decalin radical cations has been taken in dilute solutions of cis-decalin and naphthalene in liquid 3-methylpentane at 140 K. A similar spectrum has been observed in the glassy solution of 10⁻³ M naphthalene in cis-decalin. This spectrum is associated with the signals from stabilized radical cations of the solvent, cis-decalin.     

Distribution of Valence Electron Density in C n H m and BnHm Framework and Polyhedral Molecules and Orbital-Reduntant Bonds

In framework molecular cations and radical cations of adamantane C₁₀H _m ^q+ and also in polyhedral molecules and molecular ions C₅H₅ ⁺, C₆H₆ ^{2 +}, B₅H₉, and B₁₀H₁₀ ^{2 -}, the charge density of valence electrons in the central areas of C _n and B _n cavities and faces is significant. In the molecule of adamantane C₁₀H₁₆, the valence electron density in central areas of the cavity and faces of the C₁₀ framework is small as compared to the electron density along its edges C-C. These distinctions are due to the fact that, in the electronic structure of C _n H ^q _m cations and radical cations and also of B _n H _m molecules and molecular ions, there is an additional orbital interaction involving vacant valence orbitals of C⁺ or B (orbital-reduntant bonds); the absence of vacant valence orbitals of C atoms in neutral adamantane molecule excludes additional orbital interactions in excess of C-H and C-C.     

Monitoring the Light-induced Isomerisation of the Prototypical Polycyclic Aromatic Hydrocarbons C10H8+ through Ion-Molecule Reactions

Structural rearrangements in ions are essential for understanding the composition and evolution of energetic and chemically active environments. This study explores the interconversion routes for simple polycyclic aromatic hydrocarbons, namely naphthalene and azulene radical cations (C₁₀H₈⁺), by combining mass spectrometry and vacuum ultraviolet tunable synchrotron radiation through the chemical monitoring technique. Products of ion-molecule reactions are used to probe C₁₀H₈⁺ structures that are formed as a function of their internal energies. Isomerisation from azulene radical cation towards naphthalene radical cation in a timescale faster than 80 μs was monitored, whereas no reverse isomerisation was observed in the same time window. When energising C₁₀H₈⁺ with more than 6 eV, the reactivity of C₁₀H₈⁺ unveils the formation of a new isomeric group with a contrasted reactivity compared with naphthalene and azulene cations. We tentatively assigned these structures to phenylvinylacetylene cations.     

Thermal activation of methane and ethene by bare MO·+ (M=Ge, Sn, and Pb): a combined theoretical/experimental study

The thermal ion/molecule reactions (IMRs) of the Group 14 metal oxide radical cations MO ^{. +} (M=Ge, Sn, Pb) with methane and ethene were investigated. For the MO ^{. +}/CH₄ couples abstraction of a hydrogen atom to form MOH⁺ and a methyl radical constitutes the sole channel. The nearly barrier‐free process, combined with a large exothermicity as revealed by density functional theory (DFT) calculations, suggests a fast and efficient reaction in agreement with the experiment. For the IMR of MO ^{. +} with ethene, two competitive channels exist: hydrogen‐atom abstraction (HAA) from and oxygen‐atom transfer (OAT) to the organic substrate. The HAA channel, yielding C₂H₃ ^. and MOH⁺ predominates for the GeO ^{. +}/ethene system, while for SnO ^{. +} and PbO ^{. +} the major reaction observed corresponds to the OAT producing M⁺ and C₂H₄O. The DFT‐derived potential‐energy surfaces are consistent with the experimental findings. The behavior of the metal oxide cations towards ethene can be explained in terms of the bond dissociation energies (BDEs) of MO⁺? H and M⁺? O, which define the hydrogen‐atom affinity of MO⁺ and the oxophilicity of M⁺, respectively. Since the differences among the BDEs(MO⁺? H) are rather small and the hydrogen‐atom affinities of the three radical cations MO ^{. +} exceed the BDE(CH₃? H) and BDE(C₂H₃? H), hydrogen‐atom abstraction is possible thermochemically. In contrast, the BDEs(M⁺? O) vary quite substantially; consequently, the OAT channel becomes energetically less favorable for GeO ^{. +} which exhibits the highest oxophilicity among these three group 14 metal ions.     

A mass spectrometry/mass spectrometry investigation of the nature of [C10H10]+˙, [C9H7]+ and [C10H8]+˙ gas phase ions

Additional evidence for the rearrangement of the 1- and 3-phenylcyclobutene radical cations, their corresponding ring-opened 1,3-butadiene ions and 1,2-dihydronaphthalene radical cations to methylindenetype ions has been obtained for the decomposing ions by mass analysed ion kinetic energy spectroscopy (MIKES). The nature of the [C₉H₇]⁺ and [C₁₀H₈]^+˙ daughter ions arising from the electron ionization induced fragmentation of these [C₁₀H₁₀]^+˙ precursors has been investigated by collisionally activated dissociation (CAD), collisional ionization and ion kinetic energy spectroscopy. The [C₉H₇]⁺ produced from the various C₁₀H₁₀ hydrocarbons are of identical structure or an identical mixture of interconverting structures. These ions are similar in nature to the [C₉H₇]⁺ generated from indene by low energy electron ionization. The [C₁₀H₈]^+˙ ions also possess a common structure, which is presumably that of the maphthalene radical cation.     

Electrochemical Generation of the 9,10-Antraquinone Radical Anions and Its Use in the Polystyrene Synthesis

The nature of active centers and anionic mechanism of the styrene polymerization during the 9,10-antraquinone electroreduction in the monomer-dimethylacetamide-alkali metal (or ammonium) perchlorate system is studied by voltammetry, ESR, IR- and UV-spectroscopy. It is shown that the potential of electrolysis depends on the supporting electrolyte composition; the association of the supporting electrolyte cation with the organic anion, in turn, affects the mechanism of the polymerization initiation and the macromolecule growth kinetics. The potential of generation of 9,10-antraquinone and the styrene conversion in catholyte increase with increasing radius of the supporting cation in the series Li⁺ <; Na⁺ <; K⁺ <; Rb⁺ <; Cs⁺ <; (C₂H₅)₄N⁺ <; (C₄H₉)₄N⁺.     

Transition-metal mediated heteroatom removal by reactions of FeL+ [L=O,C4H6, c-C5H6, c-C5H5, C6H6, C5H4(=CH2)] with furan,thiophene, and pyrrole in the gas phase

Reactions of Fe⁺ and FeL⁺ [L=O, C₄H₆, c-C₅H₆, C₅H₅, C₆H₆, C₅H₄(=CH₂)] with thiophene, furan, and pyrrole in the gas phase by using Fourier transform mass spectrometry are described. Fe⁺, Fe(C₅H₅)⁺, and FeC₆H ₆ ⁺ yield exclusive rapid adduct formation with thiophene, furan, and pyrrole. In addition, the iron-diene complexes [FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺], as well as FeC₅H₄(=CH₂)⁺ and FeO⁺, are quite reactive. The most intriguing reaction is the predominant direct extrusion of CO from furan by FeC₄H₆ ⁺, Fe(c-C₅H₆)⁺, and FeC₅H₄(=CH₂)⁺. In addition, FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺ cause minor amounts of HCN extrusion from pyrrole. Mechanisms are presented for these CO and HCN extrusion reactions. The absence of CS elimination from thiophene may be due to the higher energy requirements than those for CO extrusion from furan or HCN extrusion from pyrrole. The dominant reaction channel for reaction of Fe(c-C₅H₆)⁺ with pyrrole and thiophene is hydrogen-atom displacement, which implies D^O(Fa(N₅H₅)⁺-C₄H₄X)>D^O(Fe(C₅H₅)⁺-H)=46±5 kcal mol^?1. D^O(Fe⁺-C₄H₄S) and D^O(Fe⁺-C₄H₅N)=D^O(Fe⁺-C₄H₆)=48±5 kcal mol^?1. Finally, 55±5 kcal mol^?1=D^O(Fe⁺-C₆H₆)>D^O(Fe⁺-C₄H₄O)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mol^?1. FeO⁺ reacts rapidly with thiophene, furan, and pyrrole to yield initial loss of CO followed by additional neutral losses. D^O(Fe⁺-CS)>D^O(Fe⁺-C₄H₄S)≈48±5 kcal mol^?1 and D^O(Fe⁺-C₄H₅N)≈48±5 kcal mol^?1>D^O(Fe⁺-HCN)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mil^?1.     

Spectral properties of the C60 complex with dibenzenechromium

The product of the interaction of fullerene C₆₀ with dibenzenechromium (DBC) was studied by ESR and IR spectroscopy. The ESR spectrum contains a signal of the radical cation DBC⁺. A signal of the C₆₀ ^? anion is virtually absent, which is most likely related to its broadening. The IR spectrum contains bands characteristic of the DBC⁺ cation in the (DBC)I molecule and four bands characteristic of C₆₀ ^?. The data obtained indicate the interaction of C₆₀ molecules with the environment in the crystal structure of the complex.     

10‐Methyl‐ and 9,10‐dimethyl­acridinium methyl sulfate

The title compounds, C₁₄H₁₂N⁺·CH₃O₄S^?, (I), and C₁₅H₁₄N⁺·CH₃O₄S^?, (II), respectively, crystallize with the planar 10‐methylacridinium or 9,10‐di­methyl­acridinium cations arranged in layers, parallel to the twofold axis in (I) and perpendicular to the 2₁ axis in (II). Adjacent cations in both compounds are packed in a `head‐to‐tail' manner. The methyl sulfate anion only exhibits planar symmetry in (II). The cations and anions are linked through C—H?O interactions involving three O atoms of the anion, six acridine H atoms and the CH₃ group on the N atom in (I), and the four O atoms of the anion, three acridine H atoms and the carbon‐bound CH₃ group in (II). The methyl sulfate anions are oriented differently in the two compounds relative to the cations, being nearly perpendicular in (I) but parallel in (II). Electrostatic interaction between the ions and the network of C—H?O interactions leads to relatively compact crystal lattices in both structures.     

Radiolysis of aqueous solutions of poly(vinyl alcohol) at 77 K

Paramagnetic products of low-temperature X-ray radiolysis of aqueous poly(vinyl alcohol) solutions (2.5 and 5% by weight) were studied by ESR spectroscopy. Experimental spectra were ascribed to a superposition of signals from hydroxyl radicals and –CH₂?^?C(OH)–CH₂? macroradicals (C_α-macroradicals), respectively. No ESR signals corresponding to trapped electrons were observed that was attributed to the peculiarities of microheterogenous structure of the frozen aqueous polymer solutions. Annealing at 115 K resulted in partial conversion of OH radicals to C_α-macroradicals. It was suggested that main part of hydroxyl radicals was stabilized in phase of polycrystalline ice while macroradicals were formed in “mixed” water–polymer phase. The radiation–chemical yields of paramagnetic species stabilized in the systems under study were determined.     

Synthese und reaktivität von dienylmetall-verbindungen: XXI. Cyclopentadienylnickel-komplexemit sterisch anspruchsvollen phosphan-liganden

Bulky phosphanes PR₃ (R = C₆H₁₁, iC₃H₇, t-C₄H₉, C₆H₄CH₃-o) stabilize complexes of type [C₅H₅Ni(PR₃)L]BF₄ (L=S(CH₃)₂, (CH₃)₃PS), from which [C₅H₅Ni(PR₃)₂]⁺ cations are obtained. Iodide replaces the sulfur ligands to yield neutral C₅H₅Ni(PR₃)I compounds. No stable [C₅H₅Ni(PR₃)]⁺ cations could be obtained by iodide abstraction, but [C₅H₅Ni(PR₃)CO]⁺ cations were formed in the presence of carbon monoxide.     

Electron spin relaxation of new organic conductors: fluroranthenyl radical cation salts

Crystals of conducting fluoranthenyl (FA) radical cation salts (FA₂)⁺X^? with X^? = PF^?₆, AsF^?₆ show ESR linewidths (ΔH_pp) of ≈15 mOe at T = 293 K at microwave(9.5 GHz) and radio frequencies (230-60 MHz). ΔH_pp is independent of orientation. We analysed longitudinal and transverse relaxation and their dependence on temperature. These salts are suitable as magnetic field probes.