Collisional activation spectra of the adduct ions of 1,2,3-triarylpropenones under ammonia chemical ionization conditions

Under ammonia chemical ionization (CI) conditions triarylpropenones undergo hydrogen radical-induced olefinic bond reduction on metal surfaces, resulting in [M + 2H + NH₄]⁺ ions corresponding to the ammonium adduct of the saturated ketone. The decomposition of the adduct ions, [MNH₄]⁺ and [M + 2H + NH₄]⁺, was studied by collision-induced dissociation mass-analysed ion kinetic energy (CID-MIKE) spectroscopy in a reverse geometry instrument. From the CID-MIKE spectra of the [MNH₄]⁺, [M + 2H + NH₄]⁺, [MND₄]⁺ and [M + 2D + ND₄]⁺ ions it is clear that the fragmentation of the adduct ions involves loss of NH₃ followed by various cyclization reactions resulting in stable condensed ring systems. Elimination of ArH and ArCHO subsequent to the loss of NH₃ and formation of aroyl ion are characteristic decomposition pathways of the [MNH₄]⁺ ions, whereas elimination of ArCH₃ and formation of [ArCH₂]⁺ are characteristic of the [M + 2H + NH₄]⁺ ions of these propenones.     

Crystal structure and charge compensation mechanism of β″-alumina type R+-gallate (R = K+, NH+4)

Single crystals of gallium analogs of K⁺- and NH⁺₄-β″-alumina (K⁺- and NH⁺₄-β″-gallate) were synthesized by ion exchanging Na⁺-β″-gallate. Crystal structures of the two gallates were refined using a single-crystal X-ray diffraction method. The positive charges due to excess K⁺ ions over the stoichiometric β-alumina composition in K⁺-β″-gallate were compensated by substituting Na⁺ ions for Ga³⁺ ions at the middle of spinel block. These Na⁺ ions were expelled from the crystals by ion exchange for NH⁺₄ ions with considerable changes in crystal structure. The excess positive charges in NH⁺₄-β″-gallate were neutralized by O²⁻ ions at the mO site associating with a new type of Frenkel defects around the conduction plane. The charge-compensation mechanism of these gallates were discussed from the crystal chemical point of view.     

Ion–molecule reaction in the gas phase 3—nucleophilic substitution of 17ξ-R-5α,14β-androstane-14,17ξ-diols under [NH4]+ chemical ionization conditions1

Under Ammonia chemical Ionization conditions the source decompositions of [M + NH₄]⁺ ions formed from epimeric tertiary steroid alchols 14 OH_β, 17OH_α or 17 OH_β substituted at position 17 have been studied. They give rise to formation of [M + NH₄? H₂O]⁺ dentoed as [MH_sH]⁺, [M_sH? H₂O]⁺, [M_sH? NH₃]⁺ and [M_sH? NH₃? H₂O]⁺ ions. Stereochemical effects are observed in the ratios [M_sH? H₂O]⁺/[M_sH? NH₃]⁺. These effects are significant among metastable ions. In particular, only the [M_sH]⁺ ions produced from trans-diol isomers lose a water molecule. The favoured loss of water can be accounted for by an S_N2 mechanism in which the insertion of NH₃ gives [M_sH]⁺ with Walden inversion occurring during the ion-molecule reaction between [M + NH₄]⁺ + NH₃. The S_N1 and S_Ni pathways have been rejected.     

Chemical composition and crystal structure of β-alumina type R+-gallate (R+ = K+, NH+4)

The crystal structures of β-alumina type K⁺-gallate (K⁺-β-gallate), Mg²⁺-doped K⁺-β-gallate, and NH⁺₄-β-gallate were refined by the single crystal X-ray diffraction method. The positive charges of excess K⁺ ions in K⁺-β-gallate were compensated by O^2? ions in the mO site which coordinated with interstitial Ga³⁺ ions. The charge compensation mechanism mentioned above was changed by doping with Mg²⁺ ions. The excess charges in Mg²⁺-doped K⁺-β-gallate were compensated by the replacement of Mg²⁺ ions for Ga³⁺ ions at the middle of spinel block. No defects were found in NH⁺₄-β-gallate for the charge compensation, which was completely consistent with the result of thermal analysis that indicated a stoichiometric composition of NH⁺₄-β-gallate.     

Quantum chemical study of the reaction of NH4+ with alkylmercury halides in the gas phase

Calculations on the thermochemistry of reactions between NH₄⁺ ions and EtHgX molecules (X = Cl, Br, I) were performed by the MNDO method. The calculations showed the possible existence of two stable isomers of composition [EtHgX, NH₄]⁺ namely [EtHgX…?HNH₃]⁺ and [EtHg(NH₃)XH]⁺. Protonation of EtHgX and of CH₂?CHHgX by NH₄⁺ is characterized by high exothermicity.     

Study of selected ions in the ammonia desorption chemical ionization mass spectra of peracetylated gentiobiose and two isotopically labelled peracetylated gentiobioses

The ammonia desorption chemical ionization (NH₃-DCI) mass spectra of peracetylated gentiobiose (1) and two isotopically labelled gentiobioses (2 and 3) were examined. Compound 2 is labelled with trideuteroacetyl groups in the non-reducing moiety and 3 with trideuteroacetyl groups in the reducing moiety. It is shown that the [M + NH₄ – 42]⁺ ion is not formed direct from [M + NH₄]⁺ by loss of ketene but appears to be formed by way of a nucleophilic acyl substitution reaction resulting in a neutral species which complexes with NH₄⁺. The disaccharides undergo cleavage at either side of the glycosidic oxygen joining the two sugar residues, a process which is accompanied by addition of H or CH₃CO to afford neutral species which complex with NH₄⁺. The structures of the ions resulting from H transfer have been inferred by comparison of their mass-analysed ion kinetic energy (MIKE) spectra with MIKE spectra of the [M + NH₄]⁺ ions of compounds of established structure. A ring fragmentation reaction of 1, 2 and 3 is reported.     

Reaction of cyclohexanone with [NH4]+ under chemical ionization conditions. 1—formation of protonated unsubstituted imines

High resolution and metastable decomposition spectra of the ions [M + NH₄]⁺ (and [M + ND₄]⁺) formed by reaction of [NH₄]⁺ (and [ND₄]⁺) with cyclohexanone have been measured. The results provide evidence that the m/z 98 ion, which is abundant in the chemical ionization (NH₃) spectrum of cyclohexanone, is in fact composed of two isobaric ions: a protonated imine ion and the molecular ion of cyclohexanone. The former is formed by a mechanism analogous to that occurring in solution.     

A study of some cations formed in the ammonia chemical ionization of ketones using mass analysed ion kinetic energy spectrometry

The structures of the major adduct ions formed in ammonia chemical ionization of thirteen aliphatic and aromatic ketones have been studied by mass analysed ion kinetic energy spectrometry. The [M+NH₃+H]⁺ ion is shown to have a protonated carbinolamine structure, [M+2NH₃+H]⁺ to be a protonated carbinolamine with hydrogen-bonded ammonia and [2M+NH₃+H]⁺ to be, at least in part, a protonated carbinolamine with hydrogen-bonded ketone. These structures may imply a nucleophilic addition of ammonia at the carbonyl of the ketone-ammonium ion complex. An unusual hydroxy migration is seen in the internal rearrangement of the [2M+NH₃+H]⁺ ion leading to the formation of a protonated imine.     

Ammonia Chemical Ionization Mass Spectra of Sydnones

The mass spectra of twenty-nine sydnones were measured by using NII₃ as a reagent gas. The [M + H + NH₃]⁺ ions are the base peaks for the entire series. Very few fragment ions were observed except for the derivatives of 4-hydroxymethylenesydnones (XXI-XXIX). Only the relatively stable sydnonyl-methylene cations are formed. With consistent formation of [M + 18]⁺ ion as the base peaks with simple spectra, the NH₃ CI-MS can be an excellent method for the molecular weight determination.     

Multiphoton ionization mass spectroscopic detection of ammonia clusters

Ammonia cluster ions (NH₃)_n?2NH⁺₄ (n = 2?8), havevbeen detected by multiphoton ionization (MPI) mass spectroscopy, incorporating both a supersonic nozzle source and an ArB excimer laser. The MPI method reveals that the intensity ratio of NH⁺₄/NH⁺₃ is more than an order of magnitude greater than that in the electron impact mass spectrum.     

The effect of K+ ion exchange on the structure and thermal reduction of hexagonal ammonium tungsten bronze

This paper discusses the changes in the structure and thermal reduction of nanosize hexagonal ammonium tungsten bronze (HATB), (NH₄)_0.33−xWO_3−y, which were caused by K⁺ ion exchange (doping) and studied by XRD, XPS, ¹H-MAS NMR, FTIR, SEM and TG/DTA-MS. Comparison of the cell parameters of undoped and doped HATB revealed that both a and c cell parameters decreased after the ion exchange reaction, which showed that smaller K⁺ ions partly replaced the larger NH₄⁺ ions in the hexagonal channels of HATB. After the reaction, from the hexagonal channels less NH₃ evolved, which also supported the incorporation of K⁺ ions into the hexagonal channels.     

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.     

Energy disposal in thermal-energy charge-transfer reactions: Ar+,Kr+ and Xe+ with NH3

Thermal-energy charge-transfer reactions from the ²P_3/2 state of Ar⁺, Kr⁺ and Xe⁺ with NH₃ are shown to be non-energy resonant: the kinetic energy released in each case has been measured, and the internal energy of the NH⁺₃ product ions deduced. Possible quenching of ²P_1/2 state of rare-gas ions in ICR cells is discussed.     

Oxidation reactions in triterpenes under chemical ionization conditions

From a collisional activation spectral study it has been found that certain triterpene alcohols with an ursane or oleanane skeleton undergo oxidation to the corresponding ketones under chemical ionization (NH₃) conditions giving rise to abundant [M + NH₄ ? 2]⁺ ions. Mass-analysed ion kinetic energy and B²/E scan results indicate that both [M + NH₄]⁺ and [M + N₂H₇ ? 2]⁺ ions contribute to the formation of the [M + NH₄ ? 2]⁺ ion.     

Ion–molecule reaction in the gas phase 4—Stereospecific nucleophilic substitution under ammonia chemical ionization conditions from diastereomeric methyl and benzyl ethers of 3-hydroxy steroids

The ammonia chemical ionization (CI/[NH₄⁺]) mass spectra of a series of diastereomeric methyl and benzyl ethers derived from 3-hydroxy steroids (unsaturated in position 5 and saturated) have been studied. The adduct ions [M+NH₄]⁺ and [MH]⁺ and the substitution product ions [M+NH₄? ROH]⁺ (thereafter called [M_sH]⁺) are characterized by an inversion in their relative stabilites in relation to their initial configuration. [M+NH₄]_α⁺ and [MH]_α⁺ formed from the α-Δ⁵-steroid isomers are stabilized by the presence of a hydrogen bond which is not possible for the β-isomers. This stereochemical effect has also been observed in the mass analysed ion kinetic energy (MIKE) spectra of [M+NH₄]⁺ and [MH]⁺. The MIKE spectra of [M_sH]⁺ indicate that those issued from the β-isomers are more stable than the one originating from the α-isomers. This behavior is also observed in the first field free region (HV scan spectra) for [MH]⁺, [M_sH]⁺ and [M+NH₄]⁺ which are precursors of the ethylenic carbocations (base peak in the conventional CI/[NH₄]⁺ spectra). Mechanisms, such as S_N1 and S_Ni, have been ruled out for the formation of [M_sH]⁺, but instead the data support an S_N2 mechanism during the ion-molecule reaction between [M+NH₄]⁺ and NH₃.     

Reactive collisions in quadrupole cells. Part I. Reaction of [CH3NH2]+˙ with the isomeric butenes and pentenes

The reactions of mass-selected [CH₃NH₂]⁺˙ ions with the isomeric butenes and pentenes were studied at low collision energies in the radiofrequency-only quadrupole collision cell of a hybrid BEqQ tandem mass spectrometer. Characteristic iminium ions arising by addition of the methylamine to the olefin followed by fragmentation are observed for but-1-ene pent-1-ene and 3-methylbut-1-ene. However, for but-2-ene pent-2-ene 2-methylpropene 2-methylbut-1-ene and 2-methylbut-2-ene the major reaction channel of [CH₃NH₂]⁺˙ is charge exchange to form the olefinic molecular ion. The isomeric olefins are characterized to a considerable extent by the characteristic ion–molecule reactions that these molecular ions undergo with the neutral olefin.     

Characterization of Cu species on SiO2 and ZSM-5 by temperature-programmed reduction by ammonia

We studied the temperature-programmed reduction by NH₃ (NH₃-TPR) as a supplement to the temperature-programmed reduction by H₂ (H₂-TPR) for the characterization of supported Cu species. The NH₃-TPR profile of Cu/SiO₂, which contained only bulk CuO, exhibited two peaks for N₂ formation in equal amounts, suggesting stepwise reduction of the bulk CuO. In contrast, the H₂-TPR profile exhibited only one H₂ consumption peak. We also studied Cu-NaZSM-5 samples with various Cu and Na loadings. The Cu ions on ZSM-5 were reduced to Cu⁺ but no further. Kinetic analysis revealed that the NH₃-TPR profile exhibited peaks for separate reductions of isolated and binuclear Cu²⁺ ions. Thus, we found NH₃-TPR to be useful for detailed analysis of the reducibility of Cu²⁺ to Cu⁺ in zeolite pores.     

Ammonia in the ion source. II. Clustering with aromatic nitro compounds

Under positive ion chemical ionization conditions with ammonla at relatively low pressure, aromatic nitro compounds do not form [M + H]⁺ ions but often form ionic clusters [M + NH₄]⁺ and [M + N₂H₇]⁺. Nitrobenzene forms a cluster [2M + NH₄]⁺ and aniline, formed by nucleophilic substitution, leads to a cluster [anilinium ion + nitrobenzene]⁺. The dinitrobenzenes form [M + NH₄]⁺ clusters and show evidence of nitroaniline formation and clustering. 1,3,5-Trinitrobenzene gives little indication of clustering or of substitution. The six isomers of trinitrotoluene appear to be stabilized by the methyl group and form clusters up to [M + N₃H₁₀]⁺. Nucleophilic substitution leads to dinitrotoluidines, which also form clusters with ammonium ions.     

Reaction from isomeric parent ions in the dissociation of dimethylpyrroles

The major dissociation pathways of the [M-H]⁺ (loss of NH₃ or CH₄) and the [M+H]⁺ (loss of NH₃ or CH₃) ions from dimethylpyrroles have been determined to occur from isomeric parent ions. For the [M-H]⁺ ion (formed by loss of a methyl hydrogen), loss of NH₃ leads to the formation of the phenylium ion and is preceded by consecutive carbon ring expansions followed by a ring contraction to form protonated aniline. Loss of CH₄ occurs after the first carbon ring expansion, which forms protonated picoline. The relative partitioning between the two dissociation paths depends upon the internal energy content of the parent ion; the highest point on the potential energy surface is the second ring expansion step. The [M+H]⁺ ion reacts through a similar pathway via dihydro analogs of picoline and aniline. The proposed reaction pathways are supported by results of semiempirical molecular orbital calculations.     

Factors affecting reactivity in ammonia chemical ionization mass spectrometry

Several factors affecting reactivity in ammonia chemical ionization mass spectrometry (NH₃ CI) have been examined. These include the sample proton affinity, the preferred site of protonation and [NH₄]⁺ attachment, and substituent effects. In general, compounds having proton affinities ?787 kJ mol^?1 do not yield analytically useful intensities of the [M·NH₄]⁺ adduct ion. Substituted aromatic compounds in which the ring is the most basic site yield little (if any) [M·NH₄]⁺ ion even if the proton affinity of the compound is greater than 787 kJ mol^?1. On the other hand, some aromatic compounds in which the substituent is the most basic site yield relatively abundant adduct ions. The spectra of compounds possessing a good leaving group (X) exhibit only weak [M·NH₄]⁺ ions, but intense [M·NH₄ ? HX]⁺ and [M ? X]⁺ ions formed by substitution and elimination reactions. Electronic effects strongly influence these processes. Several examples are presented in which isomers are readily differentiated because of different reactivities under ammonia chemical ionization conditions.