The formation of the anilinium ion from the ammonium ion in the ammonia chemical ionization of substituted benzenes

Compounds C₆H₅X(X ? F, Cl, Br, NO₂, CN, OCH₃) have been studied under chemical ionization conditions with ammonia as reagent gas. A pulsed electron beam and time resolved ion collection has allowed the determination of the reaction leading to the formation of [C₆H₅NH₃]⁺ (m/z 94). [NH₄]⁺ reacts with C₆H₅X(X ? F, Cl, Br) to yield m/z 94 but C₆H₅X (X ? CN, NO₂) forms this ion only by reactions involving either [NH₃]⁺ or [C₆H₅X]⁺. C₆H₅OCH₃ does not form m/z 94.     

Chemistry of HCNH+: mechanisms, structures, and relevance to Titan’s atmosphere

The chemistry of HCNH⁺ in Titan’s atmosphere is not completely understood despite previous experimental and theoretical studies. In response to recent suggestions in the literature, we have searched for specific products of the reactions of HCNH⁺ with H₂, CH₄, C₂H₂, and C₂H₄ using the flowing afterglow-selected ion flow tube technique. We have probed for an association mechanism for reaction with H₂, and associative-H₂ loss for the reactions involving CH₄, C₂H₂, and C₂H₄. In all cases, these reaction mechanisms were found to be inefficient pathways for the depletion of HCNH⁺. Our ab initio computational studies characterize the structures and energies for these mechanisms and indicate that the proposed pathways are endothermic or possess reaction barriers. We compare our studies to previous experimental and computational work, and we suggest other ion-neutral reactions with HCNH⁺ that have not been included in previous models of Titan’s ionosphere.     

Chemical ionization mass spectra of alkylphenol and linear alcohol polyethoxylates

The chemical ionization mass spectra of some tert-octylphenol ethoxylates and linear alcohol ethoxylates have been determined using methane and ammonia as reactant gases. Proton, [C₂H₅]⁺ and [C₃H₅]⁺ adducts were observed with attachment on the ring as well as on the oxyethylene chain for the tertiary octylphenol ethoxylates. Proton and [NH₄]⁺ addition reactions were also observed. Alkyl ion and olefin displacement reactions were also important fragmentations. Hydride abstraction and proton, [C₂H₅]⁺, [C₃H₅]⁺ and [NH₄]⁺ attachment were the most important reactions occurring for the linear alcohol ethoxylates.     

Rate coefficients at 297 K for proton transfer reactions with H2O. Comparisons with classical theories and exothermicity

Rate coefficients for proton transfer reactions of the type XH⁺ + H₂O → H₃O⁺ + X where X = H₂, CH₄, CO, N₂, CO₂ and N₂O and the type H₂O + X^? → XH + OH^? where X = H, NH₂ and C₂H₅NH have been measured at 297 K using the flowing afterglow technique. The results compare favourably with the predictions of the average-dipole-orientation theory. A trend is observed with exothermicity on a plot of (k_exp/k_ADO)_{298 K} versus ?ΔH_{298 K}⁰. The question is raised whether the relatively low probability observed for slightly exothermic proton transfer reactions is a consequence of reaction mechanism or results from the presence of a small activation energy barrier.     

A predictive model for unimolecular reactions: Reactions of unsaturated carbonium ions

The major slow unimolecular reactions undergone by C₄H₇⁺, C₅H₉⁺ and C₆H⁺₁₁ are discussed in terms of a potential surface approach and the organic chemist's concept of mechanism. It is shown that the observed decompositions which do not involve σ-bond formation in the dissociation step are precisely those expected from the model. Further use of the model correctly predicts the slow reactions of C₇H⁺₁₃ which have not previously been reported. The approach also permits useful limits to be set on the transition state energies for reactions involving σ-bond formation in the dissociation step (H₂,CH₄ loss). It is concluded that stepwise addition of ethylene to the allyl cation is preferred to a concerted 4-electron process which is symmetry forbidden.     

Mass spectra of benzenesulfonylhydrazides

The mass spectrometry of substituted benzenesulfonylhydrazides (X.C₆H₄.SO₂NHNH₂) has been studied, with X = p-CH₃, H, p-CH₃O and p-Br. The intensities of [X? C₆H₄SO₂]⁺ and [X? C₆H₄]⁺ follow the Hammett relationship [In(Z/Z₀) =ρδp⁺] with ρ of 0.375 and 2.37, respectively.     

Ion-molecule reactions of cyclopentadienyl- tricarbonylmanganese derivatives with 18-crown-6 in the gas phase

The ion-molecule reactions of 18-crown-6 (L) with ions produced from cymantrene and its derivatives under electron impact are studied. It is shown that RXC₅H₄MnL⁺ ions (RX = the substituent in the cyclopentadienyl ring) can be produced by two reaction pathways: (i) by the addition of RXC₅H₄Mn⁺ to crown ether; and (ii) by the exchange of carbonyl ligands in RXC₅H₄MnCO)_x⁺ ions (x = 1-2) for the macrocyclic molecule. The formation of RMnL⁺ ions, where R = H, Me, Ph, OH, NMe₂, proceeds via the substitution of C₅H₄X in the isomerized form of the decarbonylated ions (RMn⁺C₅H₄X) for L. The relative abundances of the RXC₅H₄MnL⁺ and RMnL⁺ ions provide information about the structure of the RXC₅H₄Mn⁺ ions. The probability of synthesizing stable “sandwich” species of the C₅H₄Mn⁺ type in the condensed phase is predicted.     

Ion/molecule reactions of ammonia and methylamine with chloro- and nitrobenzene. A comparison of chemical ionization and ion cyclotron resonance experiments

It is shown by ion cyclotron resonance measurements that ion/molecule reactions, leading to substitution or reduction product ions from chloro- and nitrobenzene with the title amines, are those between the molecular ions [RNH₂]⁺ or [C₆H₅X]⁺˙ and their respective counterparts C₆H₅X or RNH₂. The protonated reagent gas ions [RNH₃]⁺ are not involved in these reactions. In the case of nitrobenzene, adduct ions [C₆H₅NO₂·RNH₃]⁺ do not decompose within the time scale of the measurements. The results obtained are compared with those found under chemical ionization conditions.     

A theoretical study of the reaction of Ti+ with propane

Detailed quartet and doublet potential energy surfaces for the Ti⁺ + C₃H₈ → TiC₃H₆⁺ + H₂ and Ti⁺ + C₃H₈ → TiC₂H₄⁺ + CH₄ elimination reactions have been studied using density functional theory with B3LYP functional and ab initio coupled cluster CCSD(T) methods. Several H₂ elimination and CH₄ elimination reaction paths have been examined including the IRC following. In particular, the mechanisms involving, respectively, the H₂TiC₃H₆⁺ and CH₃TiHC₂H₄⁺ intermediates have been studied. Contribution to the Mark S. Gordon 65th Birthday Festschrift Issue.     

Structure and mechanism of fragmentation of [C2H5O]+

The decomposition reactions of [C₂H₅O]⁺ ions produced by dissociative electron-impact ionization of 2-propanol have been studied, using ¹³C and deuterium labeling coupled with metastable intensity studies. In addition, the fragmentation reactions following protonation of appropriately labeled acetaldehydes and ethylene oxides with [H₃]⁺ or [D₃]⁺ have been investigated. In both studies particular attention has been paid to the reactions leading to [CHO]⁺, [C₂H₃]⁺ and [H₃O]⁺. In both the electron-impact-induced reactions and the chemical ionization systems the fragmentation of [C₂H₅O]⁺ to both [H₃O]⁺ and [C₂H₃]⁺ proceeds by a single mechanism. For each case the reaction involves a mechanism in which the hydrogen originally bonded to oxygen is retained in the oxygen containing fragment while the four hydrogens originally bonded to carbon become indistinguishable. The fragmentation of [C₂H₅O]⁺ to produce [CHO]⁺ proceeds by a number of mechanisms. The lowest energy route involves complete retention of the α carbon and hydrogen while a higher energy route proceeds by a mechanism in which the carbons and the attached hydrogens become indistinguishable. A third distinct mechanism, observed in the electron-impact spectra only, proceeds with retention of the hydroxylic hydrogen in the product ion. Detailed fragmentation mechanisms are proposed to explain the results. It is suggested that the [C₂H₅O]⁺ ions formed by protonation of acetaldehyde or ionization of 2-propanol are produced initially with the structure [CH₃CH?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}H] (a), but isomerize to [CH₂?CH? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}H₂] (e) prior to decomposition to [C₂H₃]⁺ or [H₃O]⁺. The results indicate that the isomerization a → e does not proceed directly, possibly because it is symmetry forbidden, but by two consecutive [1,2] hydrogen shifts. A more general study of the electron-impact mass spectrum of 2-propanol has been made and the fragmentation reactions proceeding from the molecular ion have been identified.     

Photoionization and Dissociation Study of 2-Methyl-2-propen-1-ol: Experimental and Theoretical Insights

The photoionization and dissociation of 2-methyl-2-propen-1-ol (MPO) have been investigated by using molecular beam experimental apparatus with tunable vacuum ultravioletsynchrotron radiation in the photon energy region of 8.0-15.5 eV. The photoionization efficiency (PIE) curves for molecule ion and fragment ions: C₄H₈O⁺、C₄H₇O⁺、C₃H₅O⁺、C₄H₇⁺、C₄H₆⁺、C₄H₅⁺、C₂H₄O⁺、C₂H₃O⁺、C₃H₆⁺、C₃H₅⁺、C₃H₃⁺、CH₃O⁺、CHO⁺ have been measured, and the ionization energy (IE) and the appearance energies (AEs) of the fragment ions have been obtained. The stable species and the first order saddle points have been calculated on the CCSD(T)/cc-pvTZ//B3LYP/6-31+G(d,p) level. With combination of theoretical and experimental results, the dissociative photoionization pathways of 2-methyl-2-propen-1-ol are proposed. Hydrogen migrations within the molecule are the dominant processes in most of the fragmentation pathways of MPO.     

Kationen mit Xenon—Kohlenstoff-Bindung. 4. Salze mit monosubstituiertem Phenylxenon-Kation: Darstellung,Stabilität und Reaktivität

Cations with Xenon-Carbon Bonds. 4 Salts with Monosubstituted Phenyl Xenon Cation: Preparation, Stability and Reactivity . Nucleophilic fluorine aryl substitution reactions with monosubstituted phenylboranes (X? C₆H₄)₃B and fluorophenylboranes (X? C₆H₄)_nBF_3?n (n = 1 and 2; X = m-F, p-F, m-CF₃ and p-CF₃) on XeF₂ lead to the formation of [X? C₆H₄Xe]⁺ salts with arylfluoroborate anions [(X? C₆H₄)_nBF_4?n]^? (n = 2, 1 and 0). Their thermal behaviour, their spectroscopic properties and first investigations concerning their reactivity are reported.     

Reactions of hydrocarbon ions with hydrogen and methane at 300 K

The rate coefficients and ionised product distributions have been determined for reactions of the ions CH⁺_n and C₂H⁺_n with H₂ and CH₄, for n = 0 to 4, in a SIFT apparatus at 300 K. The reactions are fast and multiple products result from the CH₄ reactions.     

A Theoretical Investigation on the Reaction Mechanism of the C8H10+· Side‐Chain Decomposition Processes

The dissociation of ethylbenzene cation C₈H₁₀^+· served as a prototype to investigate the decompasition mechanisms of alkylbenzene cations. The reactions of C₈H₁₀^+· decomposition reaction system have been studied extensively at the B3LYP/6‐311++G?? ?? level with Gaussion 98 package. The chain reaction of C₈H₁₀^+· dissociation is initiated by C–H bond rupture. All reaction channels were fully investigated with the vibrational mode analysis to confirm the transition states and reveal the reaction mechanism. The energetically most favorable pathway is C₈H₁₀^+·→TS4→P2+H· and the channel leading to C₈H₁₀^+· and C₂H₄ is also competitive.     

Molecular fragmentations: Part VII. Structures and energies of mass spectral fragments derived from benzene

Molecular structures and energies have been calculated, using MINDO/3, of the mass spectral ions arising from benzene: (C₆H₆)⁺ (three non-valence isomers); (C₆H₅⁺); (C₅H₃⁺) (four isomers); (C₄H₄)⁺ (three isomers); (C₄H₃)⁺ (two isomers); (C₄H₂)⁺ (four isomers); (C₃H₃)⁺; and (C₂H₂)⁺. Calculations have been made for the conjugate neutral fragments, allowing calculation of appearance potentials, and also for the ion (C₆H₇)⁺.     

Charge neutralization of ions from benzene

Cross-sections have been measured for the charge neutrilization if ions from benzene in kiloelectron-volt collisions with benezene target molecules. Measured values range from 65 Ų for the symmetric [C₆H₆]⁺? C₆H₆ resonant reactions to 8 Ų for [C₃H₃]⁺? C₆H₆ reactions. Cross-sections computed using a simple resonance charge transfer model compare favourably with experimental data for the symmetric reactions. The cross-sections for asymmetric reactions are smaller that those for they symmetric system and magnitudes of the asymmetric cross-sections are correlated with recombination energies of the respective ions.     

SiH+5 and the proton affinity of monosilane

Tandem mass spectrometric studies show that SiH⁺₅ is formed in bimolecular reactions of SiH₄ and NH⁺₂, C₂H⁺₃, C₂H⁺₆ and C₃H⁺₈ ions. The dependence of the reaction cross sections on ion energy indicates the formation of SiH⁺₅ from NH⁺₂, C₂H⁺₃, and C₂H⁺₆ to be exothermic reactions, while formation from C₃H⁺₈ is endothermic. Using known thermochemical data, these facts permit the assignment of 150 and 156 kcal/mole to the lower and upper limits of the proton affinity of monosilane.     

Nitrosyl Rhenium Complexes Syntheses,Properties, and Structures of Oxalato Derivatives

The free acid, H[Re(NO)(C₂O₄)(OH)₂(H₂O)] has been prepared from the reaction of Re(NO)(OH)₃ ? H₂O with oxalic acid in aqueous medium. The K⁺, NH₄⁺ and Pb²⁺ salts of the acid have been isolated. Nonelectrolytic diimino derivatives, Re(NO)(C₂O₄)X · L (X = 1, 10-phenanthroline, 2,2′-dipyridyl; L ? OH^?, Cl^?) have been synthesized. The complexes have been characterised through elemental analyses, spectral (u.v., vis., i.r.) properties, magnetic and conductance data and their structures are proposed.     

C-C and C-H bond activation in the fragmentation of the [M + Ni]+ adducts of aliphatic amino acids

The major metal-containing species formed upon fast atom bombardment of amino acid/Ni⁺² mixtures is the [M + Ni]⁺ adduct, involving reduction of the Ni⁺² to the +1 oxidation state. By contrast, electrospray ionization of amino acid/Ni⁺² mixtures produces predominantly [Ni(M ? H)M]⁺; this species, on collisional activation, produces predominantly [M + Ni]⁺ by elimination of [M - H], presumably a carboxylate radical. The unimolecular fragmentation reactions occurring on the metastable ion time scale for the [M + Ni]⁺ adducts of a variety of α-amino acids have been recorded. The adducts with phenylalanine, α-aminoisobutyric acid and α-aminobutyric acid fragment by elimination of H₂O, H₂O + CO and, to a minor extent, by elimination of CO₂. These reactions are similar to those observed for the [M + Cu]⁺ adducts of α-amino acids. A reaction distinctive for the [M + Ni]⁺ adducts involves formation of the immonium ion RCH=NH ₂ ⁺ . By contrast, the [M + Ni]⁺ adducts with leucine, isoleucine, and norleucine show extensive metastable ion fragmentation by elimination of H₂, CH₄, C₂H₄, C₃H₆, and C₄H₈, with the relative importance of the different fragmentation channels depending on the configuration of the C₄H₉ side chain. These results are interpreted in terms of C-C and C-H bond activation of the C₄H₉ side chain by the Ni⁺. The adducts with valine and norvaline fragment in a fashion similar to the adduct with phenylalanine, except that minor elimination of C₃H₆ is observed.     

Structure and fragmentation of [C6H13O]+ ions formed by chemical ionization

The structure and fragmentation of eight [C₆H₁₃O] ⁺ ions formed by protonation of C₆H₁₂O carbonyl compounds in the gas phase have been investigated using isotopic labeling and metastable ion studies to investigate the fragmentation reactions and collisional dissociation studies to probe ion structures. Protonated 3-methyl-2-pentanone and protonated 2-methyl-3-pentanone readily-interconvert by pinacolic-retro-pinacolic rearrangements; the remaining six ions represent stable ion structures, although in many cases fragmentation is preceded by pinacolic-type rearrangements. Unimolecular (metastable ion) fragmentation of the [C₆H₁₃O] ⁺ species occurs by elimination of H₂O, C₃H₆, C₄H₈ and C₂H₄O. The last three elimination reactions appear to occur through the intermediacy of a proton-bound complex of a carbonyl compound and an olefin, with the proton residing with the species of higher proton affinity on decomposition of the complex.