[C7H7] radicals studied by neutralization reionization mass spectrometry; the ortho-tolyl to benzyl radical rearrangement

The collision-induced dissociation characteristics of the benzyl, tropyl and tolyl cations which serve to identify these [C₇H₇]⁺ isomers (the m/z 74–77 relative abundances) were not preserved in their neutralization-reionization (NR) mass spectra. However, analyses of mixtures of the [C₇H₇]⁺ isomers made by comparison of NR mass spectra gave similar results to those obtained from collisional activation (CA) mass spectra. The radicals produced by electron transfer from Xe to tolyl cations were not observed to rearrange to benzyl radicals on the time-scale of the NR experiment, a result in conflict with other gas-phase studies.     

Chemical consequences of electron scavenging by SF6 in radiolysis experiments

Contrary to the usual assumption that it is unreactive, SF₆^? formed by electron attachment is found to undergo rapid bimolecular reactions with molecules (HX) possessing acidic hydrogen, including HCl, HBr, HCO₂H, CH₃CO₂H, H₂S, and HCN. It is clear for many systems that meaningful mechanistic inferences about radiolytic processes occurring in the presence of SF₆ should consider a wide variety of non-scavenging reactions. Appropriate caution should be exercised in any experiment in which SF₆ is used to scavenge and detect low energy electrons. The reaction sequences observed are interesting in that they provide convenient bimolecular pathways for the formation of a variety of anionic dimers of the type XHY^?.     

Neutralization-reionization study of C6H6O isomers

Neutralization-reionization (⁺NR⁺) mass spectrometry is employed to examine the behavior of C₆H₆O isomers in the gas phase. Phenol and cyclohexa-2,4-dienone are found not to interconvert following neutralization with mercury of their corresponding cation radicals at 9.9 keV kinetic energy. A very low extent of isomerization is observed following collisional activation of fast C₆H₆O neutrals with helium. The ⁺NR⁺ and collisionally activated dissociation spectra, the latter obtained at unit mass resolution, are used to identify these [C₆H₆O]^{+ ˙} isomers. Hexa-1,3,5-trienal is found to cyclize spontaneously to cyclohexa-2,4-dienone during attempted pyrolytic preparation. The thermochemistry of these C₆H₆O molecules and cation radicals is discussed on the basis of experimental data and MNDO calculations.     

Neutralization-reionization mass spectrometry (NRMS). Structural information from vertical neutralization and reionization efficiencies

The neutralization-reionization mass spectra of alkane radical ions indicate significant differences between the structures and geometries of alkane molecules and their molecular ions, confirming recent ab initio predictions. Ionic isomers that are indistinguishable by collisionally-activated dissociation because of easy interconversion can be characterized by neutralization-reionization if the corresponding neutrals show different reactivities, as is demonstrated for the [C₂H₅]⁺/C₂H₅˙ system and for [C₂H₄O₂]⁺˙ isomers. For identification of mixtures of more than one neutral species, the relative efficiency for reionizing each neutral must be determined; e.g. the O₂ reionization efficiency of ˙CH₂OH radicals is ～4 times greater than that of CH₃O˙. This information and reference reionization spectra of CH₃O˙ and ˙CH₂OH show that metastable or collisionally activated methyl acetate cations lose CH₃O˙, not ˙CH₂OH as previously reported; the newly-formed CH₃O˙ undergoes partial (～20%) isomerization to ˙CH₂OH in the ～10^?6s before reionization. Similar results are obtained for [B(OCH₃)₃]⁺˙.     

Neutralization–reionization efficiencies for gaseous [C3Hn]+ Ions

A neutralization-reionization study of [C₃H_n]⁺ ions, n = 6?0, shows that neutralization efficiencies are larger for hydrocarbon radical cations than they are for even-electron carbocations with one more H atom. Reionization efficiencies to positive ions do not depend appreciably on the electronic properties of the neutral species undergoing reionization. However, reionization efficiencies to negative ions increase dramatically with the degree of unsaturation, by nearly two orders of magnitude, from C₃H₆ to C₃. All C₃H_n neutrals studied survive intact neutralization to produce a considerable fraction of stable, non-dissociating [C₃H_n]⁺ upon cationization. All C₃H_n radicals (n = 5, 3, 1) can be transferred collisionally to stable even-electron anions. For the C₃H_n hydrocarbon molecules studied (n = 6, 4, 2, 0) the stability of the molecular radical anion increases substantially with the degree of unsaturation.     

Über Chalkogenolate,LVI. Untersuchungen über Thioameisensäuren 4. Verhalten von [HCO2]−, [HCOS]− und [HCS2]− in wäßriger Lösung

The behaviour of Na[HCO₂], Na[HCOS], and K[HCS₂] in aqueous solutions between 4 and 42°C was investigated by means of conductivity measurements. The equivalent conductivities Λ of [HCO₂]^?, [HCOS]^?, and [HCS₂]^? and the dissociation constants K_c of HCOSH and HCSSH were determined. The STOKES radii of the ions, the radii of the hydrated ions, and their diffusion coefficients were calculated.     

Reversible and Selective CO2 to HCO2− Electrocatalysis near the Thermodynamic Potential

Reversible catalysis is a hallmark of energy‐efficient chemical transformations, but can only be achieved if the changes in free energy of intermediate steps are minimized and the catalytic cycle is devoid of high transition‐state barriers. Using these criteria, we demonstrate reversible CO₂/HCO₂^? conversion catalyzed by [Pt(depe)₂]²⁺ (depe=1,2‐bis(diethylphosphino)ethane). Direct measurement of the free energies associated with each catalytic step correctly predicts a slight bias towards CO₂ reduction. We demonstrate how the experimentally measured free energy of each step directly contributes to the <50 mV overpotential. We also find that for CO₂ reduction, H₂ evolution is negligible and the Faradaic efficiency for HCO₂^? production is nearly quantitative. A free‐energy analysis reveals H₂ evolution is endergonic, providing a thermodynamic basis for highly selective CO₂ reduction.     

Sind die ‚Lehrbuch-Anionen’︁ O2−, [CO3]2− und [SO4]2− Fiktionen?

Are the ‘Textbook Anions’ O^2?, [CO₃]^2?, and [SO₄]^2? Fictitious? Experimental second electron affinities are still unknown for the title anions. It will be shown by means of quantum chemical ab initio calculations that these dianions are unstable with respect to spontaneous ionization. They all must be designated as non-existent.     

Solution Synthesis,Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}−

The first crystallographically characterizable complex of Sc²⁺, [Sc(NR₂)₃]⁻ (R=SiMe₃), has been obtained by LnA₃/M reactions (Ln=rare earth metal; A=anionic ligand; M=alkali metal) involving reduction of Sc(NR₂)₃ with K in the presence of 2.2.2‐cryptand (crypt) and 18‐crown‐6 (18‐c‐6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]⁺, [K(18‐c‐6)]⁺, and [Cs(crypt)]⁺ salts of the [Sc(NR₂)₃]⁻ anion are formed, respectively. The formation of this oxidation state of Sc is also indicated by the eight‐line EPR spectra arising from the I =7/2 ⁴⁵Sc nucleus. The Sc(NR₂)₃ reduction differs from Ln(NR₂)₃ reactions (Ln=Y and lanthanides) in that it occurs under N₂ without formation of isolable reduced dinitrogen species. [K(18‐c‐6)][Sc(NR₂)₃] reacts with CO₂ to produce an oxalate complex, {K₂(18‐c‐6)₃}{[(R₂N)₃Sc]₂(μ‐C₂O₄‐κ ¹O:κ ¹O′′)}, and a CO₂⁻ radical anion complex, [(R₂N)₃Sc(μ‐OCO‐κ ¹O:κ ¹O′)K(18‐c‐6)]_n .     

Die Kristallstruktur des SF5−-Anions

Crystal Structure of the SF₅^?-Anion The carbanion SF₅? C(CF₃)₂^? decomposes slowly forming SF₅^?, and (CF₃)₂C?C(CF₃)₂. The pentafluorosulfates(IV) grow in large crystals which are stable for prolonged times in presence of a SF₄ vapour pressure. Crystal structure analysis of Rb⁺SF₅^? (Pbnm, a = 776.1(14), b = 990.3(5), c = 614.1(3) pm, Z = 4) revealed the SF₅^? anion in the expected square pyramidal structure. The axial bond is 15.9 pm shorter than the average equatorial bonds. The sulfur atom is located below the equatorial fluorine atoms. Pure Cs⁺SF₅^?-crystals seem to be notoriously twinned. Accidentally we isolated a double salt (Cs⁺)₆(SF₅^?)₄ (HF₂^?)₂ (P4 b2, a = 1031.7(15), c = 627.6(9) pm, Z = 1). Herein the anion SF₅^? has the same structure as in Rb⁺SF₅^?.     

Structural identification of fatty acid methyl esters by collision spectra of their [M ? H]− species

Negative ion chemical ionization linked to collisionally activated decomposition (CAD) experiments has proved to be an efficient analytical tool in mass spectrometric characterization of fatty acids. The CAD mass-analysed ion kinetic energy spectra of [M ? H]^? species, obtained by OH^? reaction with a selection of six C₁₈ fatty acid methyl esters, reveal useful correlations with the original structure of the neutrals, giving evidence of both chain branching and double bond positions.     

Solution Synthesis,Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}−

The first crystallographically characterizable complex of Sc²⁺, [Sc(NR₂)₃]⁻ (R=SiMe₃), has been obtained by LnA₃/M reactions (Ln=rare earth metal; A=anionic ligand; M=alkali metal) involving reduction of Sc(NR₂)₃ with K in the presence of 2.2.2‐cryptand (crypt) and 18‐crown‐6 (18‐c‐6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]⁺, [K(18‐c‐6)]⁺, and [Cs(crypt)]⁺ salts of the [Sc(NR₂)₃]⁻ anion are formed, respectively. The formation of this oxidation state of Sc is also indicated by the eight‐line EPR spectra arising from the I =7/2 ⁴⁵Sc nucleus. The Sc(NR₂)₃ reduction differs from Ln(NR₂)₃ reactions (Ln=Y and lanthanides) in that it occurs under N₂ without formation of isolable reduced dinitrogen species. [K(18‐c‐6)][Sc(NR₂)₃] reacts with CO₂ to produce an oxalate complex, {K₂(18‐c‐6)₃}{[(R₂N)₃Sc]₂(μ‐C₂O₄‐κ ¹O:κ ¹O′′)}, and a CO₂⁻ radical anion complex, [(R₂N)₃Sc(μ‐OCO‐κ ¹O:κ ¹O′)K(18‐c‐6)]_n .     

High energy collisional spectroscopy of [RCOO]− anions from negative ion chemical ionization of fatty acid methyl esters

Saturated and mono-unsaturated fatty acid methyl esters as well as corresponding underivatized acids gave abundant carboxylate anions [RCOO]^? under negative ion chemical ionization (OH^? and NH₂ ^?) and electron attachment conditions. B/E or mass-analysed ion kinetic energy spectra of fragments arising from high energy collision activated dissociation (CAD) of these [RCOO]^? species contained decisive information on the original structure of the neutrals. From an analytical point of view, the method can utilize the gas chromatographic mass spectrometric combination and, in the B/E mode, can be used in practice on any double-focusing mass spectrometer.     

Salts of HCN‐Cyanide Aggregates: [CN(HCN)2]− and [CN(HCN)3]−

Although pure hydrogen cyanide can spontaneously polymerize or even explode, when initiated by small amounts of bases (e.g. CN^?), the reaction of liquid HCN with [WCC]CN (WCC=weakly coordinating cation=Ph₄P, Ph₃PNPPh₃=PNP) was investigated. Depending on the cation, it was possible to extract salts containing the formal dihydrogen tricyanide [CN(HCN)₂]^? and trihydrogen tetracyanide ions [CN(HCN)₃]^? from liquid HCN when a fast crystallization was carried out at low temperatures. X‐ray structure elucidation revealed hydrogen‐bridged linear [CN(HCN)₂]^? and Y‐shaped [CN(HCN)₃]^? molecular ions in the crystal. Both anions can be considered members of highly labile cyanide‐HCN solvates of the type [CN(HCN)_n]^? (n=1, 2, 3 …) as well as formal polypseudohalide ions.     

Double collision experiments

A variety of double collision experiments, whereby fast species undergo collisional interactions in two distinct regions of a mass spectrometer, are described. These include two-stage charge reversal of negative ions, two-stage double electron transfer from targets to cations, neutralization-reionization experiments as well as delayed analysis of organic cations formed in a one-step charge reversal of anions. Experiments have been performed on a number of systems of current interest in gas-phase ion chemistry. It is concluded that autoelectron detachment of benzyl anions leads to benzyl radicals, whereas the collisionally induced electron detachment produces a mixture of benzyl and tropyl radicals. By contrast, electron detachment from [H₃CNH]^? is not a metastable process and occurs only after excitation to produce H₃CNH˙ radicals, which do not rearrange into the thermodynamically more stable H₂CNH₂˙. It is shown that in the double electron transfer reactions H⁺ + Xe→H˙ + Xe⁺˙ and H˙ + Xe→H^? + Xe⁺˙, excited states are produced. From double collision experiments on methyl formate ions, it is concluded that the non-decomposing ions have undergone rearrangement on the time-scale of 10 μs into the distonic isomer, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H} - \mathop {\rm C}\limits^ + ({\rm OH}){\rm O}\mathop {\rm C}\limits^. {\rm H}_2 $\end{document}. Finally, it is shown that short-lived (<0.2 μs) [H₂, C, N]⁺ ions generated by charge-reversal of [H₂CN]^? have the [H₂CN]⁺ structure, whereas most of the long-lived (10 μs) ions have the [HCNH]⁺ structure.     

Darstellung und spektroskopische Charakterisierung der Persulfoniumsalze (CH3)(CF3)SF3+SbF6− und (CH3)(CF3)2SF2+SbF6− und Kristallstruktur von CF3SF2+SbF6−

Preparation and Spectroscopic Characterization of the Persulfonium Salts (CH₃)(CF₃)SF₃⁺SbF₆^? and (CH₃)(CF₃)₂SF₂⁺SbF₆^? and Crystal Structure of CF₃SF₂⁺SbF₆^? [1] . The preparation of the persulfonium salts (CH₃)(CF₃)SF₃⁺SbF₆^? and (CH₃)(CF₃)₂SF₂⁺SbF₆^? by methylation of the sulfuranes CF₃SF₃ and (CF₃)₂SF₂ with CH₃OSO⁺SbF₆^? in liquid SO₂ is reported. The thermolabile compounds are characterized by IR, Raman, ¹H, ¹³C, and ¹⁹F NMR spectroscopy. CF₃SF₂⁺SbF₆^? crystallizes in the space group C2/c with a=16.889(8) Å, b=7.261(4) Å, c=13.416(7) Å, β=91.08° with 8 formula units per unit cell at 167 K. Cations and anions are connected via short SF contacts forming a Ψ-octahedral surrounding of the central S atom which is in close analogy to the already known CF₃SF₂⁺AsF₆^?.     

Spectroelectrochemical Investigation of TPPMn(III/II)‐Driven Liquid | Liquid | Electrode Triple Phase Boundary Anion Transfer into 4‐(3‐Phenylpropyl)‐Pyridine: ClO4−, CO3H−, Cl−, and F−

The triple phase boundary transfer of anions from the aqueous into an organic phase can be driven electrochemically here with the tetraphenylporphyrinato‐Mn(III/II) (or TPPMn) redox system in 4‐(3‐phenylpropyl)‐pyridine) (or PPP). Anions investigated are perchlorate, chloride, fluoride, and bicarbonate. The bicarbonate and fluoride transfer processes are shown to be chemically more complex compared to the perchlorate and chloride cases with UV‐vis‐spectroelectrochemical measurements indicating a combination of HCO₃^?/CO₃^2? transfer processes and association of fluoride with TPPMn(III)⁺, respectively. In situ spectroelectrochemistry is developed for ion‐transfer voltammetry into sub‐microliter organic phase regions on mesoporous ITO conducting film electrodes.     

The [CH5NO]+ ˙ potential energy surface: Distonic ions,lon-dipole complexes and hydrogen-bridged radical cations

By combining results from a variety of mass spectrometric techniques (metastable ion, collisional activation, collision-induced dissociative ionization, neutralization-reionization spectrometry, ²H, ¹³C and ¹⁸O isotopic labelling and appearance energy measurements) and high-level ab initio molecular orbital calculations, the potential energy surface of the [CH₅NO]^{+ ˙} system has been explored. The calculations show that at least nine stable isomers exist. These include the conventional species [CH₃ONH₂]^{+ ˙} and [HO? CH₂? NH₂]^{+ ˙}, the distonic ions [O? CH₂? NH₃]^{+ ˙}, [O? NH₂? CH₃]^{+ ˙}, [CH₂? O(H)? NH₂]^{+ ˙}, [HO? NH₂? CH₂]^{+ ˙}, and the ion-dipole complex CH₂?NH₂⁺ …? OH˙. Surprisingly the distonic ion [CH₂? O? NH₃]^{+ ˙} was found not to be a stable species but to dissociate spontaneously to CH₂?O + NH₃^{+ ˙}. The most stable isomer is the hydrogen-bridged radical cation [H? C?O …? H …? NH₃]^{+ ˙} which is best viewed as an immonium cation interacting with the formyl dipole. The related species [CH₂?O …? H …? NH₂]^{+ ˙}, in which an ammonium radical cation interacts with the formaldehyde dipole is also a very stable ion. It is generated by loss of CO from ionized methyl carbamate, H₂N? C(?O)? OCH₃ and the proposed mechanism involves a 1,4-H shift followed by intramolecular ‘dictation’ and CO extrusion. The [CH₂?O …? H …? NH₂]^{+ ˙} product ions fragment exothermically, but via a barrier, to NH₄^{+ ˙} HCO^…? and to H₃N? C(H)?O^{+ ˙} H˙. Metastable ions [CH₃ONH₂]^+…? dissociate, via a large barrier, to CH₂?O + NH₃⁺ + and to [CH₂NH₂]⁺ + OH˙ but not to CH₂?O^{+ ˙} + NH₃. The former reaction proceeds via a 1,3-H shift after which dissociation takes place immediately. Loss of OH˙ proceeds formally via a 1,2-CH₃ shift to produce excited [O? NH₂? CH₃]^{+ ˙}, which rearranges to excited [HO? NH₂? CH₂]^{+ ˙} via a 1,3-H shift after which dissociation follows.     

A flowing afterglow study of [C3H3]− ions generated from the reactions of [OH]− with allene and propyne

Flowing afterglow studies are reported for the rates and modes of reaction of [C₃H₃]^? ions produced from allene and propyne by reaction with [OH]^? or by electron impact. Studies with methyl formate provide further evidence for the formation from propyne of two distinct stable species.     

Darstellung und Konfiguration von Tricarbonylchromat-Anionen mit SnCl3− und GeCl3− als Liganden

B₃N₃Me₆Cr(CO)₃ reacts with [AsPh₄] [SnCl₃] and [AsPh₄] [GeCl₃] in tetrahydrofuran to give [AsPh₄]₃[Cr(CO)₃(SnCl₃)₃] and [AsPh₄]₃[Cr(CO)₃(GeCl₃)₃], respectively. According to IR. and ¹³C-NMR.-data, the tricarbonylate anions possess a meridional configuration. The donor-acceptor properties of SnCl₃^? and GeCl₃^? in the anions [Cr(CO)₃(ECl₃)₃]^3? (E = Sn, Ge) are very similar. A similar synthesis of [AsPh₄]₃[Cr(CO)₃(SnF₃)₃] was not successful.