Energy dependence of the fragmentation of some isomeric [C6H12]+˙ ions

The charge exchange mass spectra of 14 C₆H₁₂ isomers have been determined using [CS₂]^+˙, [COS]^+˙, [Xe]^+˙, [CO]^+˙, [N₂]^+˙ and [Ar]^+˙ as the major reactant ions covering the recombination energy range from ∼10.2 eV to ∼15.8 eV. From the charge exchange data breakdown graphs have been constructed expressing the energy dependence of the fragmentation of the isomeric [C₆H₁₂]^+˙ molecular ions. The electron impact mass spectra are discussed in relation to these breakdown graphs and approximate internal energy distribution functions derived from photoelectron spectra.     

Solid‐state architecture of saccharin salts of some diamines

Hydrazinium saccharinate, N₂H₅⁺·C₇H₄NO₃S⁻, crystallizes in a 1:1 ratio, while ethyl­ene­diaminium bis­(saccharinate), C₂H₁₀N₂²⁺·2C₇H₄NO₃S⁻, and butane‐1,4‐diaminium bis­(sac­charin­ate), C₄H₁₄N₂²⁺·2C₇H₄NO₃S⁻, form in a 1:2 cation–anion stoichiometry. The structures contain many strong hydrogen bonds of the N⁺—H⋯N⁻, N⁺—H⋯O, N—H⋯O and N—H⋯N types, with auxiliary C—H⋯O inter­actions.     

Three‐dimensional networks in 5‐methylimidazolium 3‐carboxy‐4‐hydroxybenzenesulfonate and bis(5‐methylimidazolium) 3‐carboxylato‐4‐hydroxybenzenesulfonate

The two title proton‐transfer compounds, 5‐methylimidazolium 3‐carboxy‐4‐hydroxybenzenesulfonate, C₄H₇N₂⁺·C₇H₅O₆S⁻, (I), and bis(5‐methylimidazolium) 3‐carboxylato‐4‐hydroxybenzenesulfonate, 2C₄H₇N₂⁺·C₇H₅O₆S²⁻, (II), are each organized into a three‐dimensional network by a combination of X—H...O (X = O, N or C) hydrogen bonds, and π–π and C—H...π interactions.     

Distinguishing two isomeric mephedrone substitutes with selective reagent ionisation mass spectrometry (SRI‐MS)

The isomers 4‐methylethcathinone and N‐ethylbuphedrone are substitutes for the recently banned drug mephedrone. We find that with conventional proton transfer reaction mass spectrometry (PTR‐MS), it is not possible to distinguish between these two isomers, because essentially for both substances, only the protonated molecules are observed at a mass‐to‐charge ratio of 192 (C₁₂H₁₈NO⁺). However, when utilising an advanced PTR‐MS instrument that allows us to switch the reagent ions (selective reagent ionisation) from H₃O⁺ (which is commonly used in PTR‐MS) to NO⁺, O₂⁺ and Kr⁺, characteristic product (fragment) ions are detected: C₄H₁₀N⁺ (72 Da) for 4‐methylethcathinone and C₅H₁₂N⁺ (86 Da) for N‐ethylbuphedrone; thus, selective reagent ionisation MS proves to be a powerful tool for fast detection and identification of these compounds. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Z and E isomers of butenedioic acid with 2‐amino‐1,3‐thiazole: 2‐amino‐1,3‐thiazolium hydrogen maleate and 2‐amino‐1,3‐thiazolium hydrogen fumarate

Maleic acid and fumaric acid, the Z and E isomers of butenedioic acid, form 1:1 adducts with 2‐amino‐1,3‐thiazole, namely 2‐amino‐1,3‐thiazolium hydrogen maleate (2ATHM), C₃H₅N₂S⁺·C₄H₃O₄⁻, and 2‐amino‐1,3‐thiazolium hydrogen fumarate (2ATHF), C₃H₅N₂S⁺·C₄H₃O₄⁻, respectively. In both compounds, protonation of the ring N atom of the 2‐amino‐1,3‐thiazole and deprotonation of one of the carboxyl groups are observed. The asymmetric unit of 2ATHF contains three independent ion pairs. The hydrogen maleate ion of 2ATHM shows a short intramolecular O—H...O hydrogen bond with an O...O distance of 2.4663 (19) Å. An extensive hydrogen‐bonded network is observed in both compounds, involving N—H...O and O—H...O hydrogen bonds. 2ATHM forms two‐dimensional sheets parallel to the ab plane, extending as independent parallel sheets along the c axis, whereas 2ATHF forms two‐dimensional zigzag layers parallel to the bc plane, extending as independent parallel layers along the a axis.     

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)⁺.     

A solid‐state oxidation of 1,1,3,3‐tetramethylguanidinium 4‐methylbenzenesulfinate to 1,1,3,3‐tetramethylguanidinium 4‐methylbenzenesulfonate

The organic acid–base complex 1,1,3,3‐tetramethylguanidinium 4‐methylbenzenesulfonate, C₅H₁₄N₃⁺·C₇H₇O₃S⁻, was obtained from the corresponding 1,1,3,3‐tetramethylguanidinium 4‐methylbenzenesulfinate complex, C₅H₁₄N₃⁺·C₇H₇O₂S⁻, by solid‐state oxidation in air. Comparison of the two crystal structures reveals similar packing arrangements in the monoclinic space group P2₁/c, with centrosymmetric 2:2 tetramers being connected by four strong N—H...O=S hydrogen bonds between the imine N atoms of two 1,1,3,3‐tetramethylguanidinium bases and the O atoms of two acid molecules.     

Two‐component molecular crystals from N‐heteroaromatics and nitro­benzoic acids

Five two‐component molecular crystals, benzimidazolium 3‐nitro­benzoate, C₇H₇N₂⁺·C₇H₄NO₄^?, (I), benzimidazolium 4‐nitro­benzoate, C₇H₇N₂⁺·C₇H₄NO₄^?, (II), 1H‐benzotriazole–3‐nitro­benzoic acid (1/1), C₆H₅N₃·C₇H₅NO₄, (III), imidazol­ium 3‐nitro­benzoate, C₃H₅N₂⁺·C₇H₄NO₄^?, (IV), and imid­azolium 4‐nitro­benzoate, C₃H₅N₂⁺·C₇H₄NO₄^?, (V), were prepared with the aim of making chiral crystals. Only (I) crystallizes in a chiral space group. The mol­ecules of (I) and (II) are linked by hydrogen bonds to form 2₁ spiral chains. In (III), (IV) and (V), macrocyclic structures are formed from two acid and two base components, by an alternate arrangement of the acid and base moieties.     

Eight salt forms of sulfadiazine

Proton transfer to the sulfa drug sulfadiazine [systematic name: 4‐amino‐N‐(pyrimidin‐2‐yl)benzenesulfonamide] gave eight salt forms. These are the monohydrate and methanol hemisolvate forms of the chloride (2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium chloride monohydrate, C₁₀H₁₁N₄O₂S⁺·Cl⁻·H₂O, (I), and 2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium chloride methanol hemisolvate, C₁₀H₁₁N₄O₂S⁺·Cl⁻·0.5CH₃OH, (II)); a bromide monohydrate (2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium bromide monohydrate, C₁₀H₁₁N₄O₂S⁺·Br⁻·H₂O, (III)), which has a disordered water channel; a species containing the unusual tetraiodide dianion [bis(2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium) tetraiodide, 2C₁₀H₁₁N₄O₂S⁺·I₄²⁻, (IV)], where the [I₄]²⁻ ion is located at a crystallographic inversion centre; a tetrafluoroborate monohydrate (2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium tetrafluoroborate monohydrate, C₁₀H₁₁N₄O₂S⁺·BF₄⁻·H₂O, (V)); a nitrate (2‐{[(4‐azaniumylphenyl)sulfonyl]azanidyl}pyrimidin‐1‐ium nitrate, C₁₀H₁₁N₄O₂S⁺·NO₃⁻, (VI)); an ethanesulfonate {4‐[(pyrimidin‐2‐yl)sulfamoyl]anilinium ethanesulfonate, C₁₀H₁₁N₄O₂S⁺·C₂H₅SO₃⁻, (VII)}; and a dihydrate of the 4‐hydroxybenzenesulfonate {4‐[(pyrimidin‐2‐yl)sulfamoyl]anilinium 4‐hydroxybenzenesulfonate dihydrate, C₁₀H₁₁N₄O₂S⁺·HOC₆H₄SO₃⁻·2H₂O, (VIII)}. All these structures feature alternate layers of cations and of anions where any solvent is associated with the anion layers. The two sulfonate salts are protonated at the aniline N atom and the amide N atom of sulfadiazine, a tautomeric form of the sulfadiazine cation that has not been crystallographically described before. All the other salt forms are instead protonated at the aniline group and on one N atom of the pyrimidine ring. Whilst all eight species are based upon hydrogen‐bonded centrosymetric dimers with graph set R₂²(8), the two sulfonate structures also differ in that these dimers do not link into one‐dimensional chains of cations through NH₃‐to‐SO₂ hydrogen‐bonding interactions, whilst the other six species do. The chloride methanol hemisolvate and the tetraiodide are isostructural and a packing analysis of the cation positions shows that the chloride monohydrate structure is also closely related to these.     

N—H...S and C—H...S hydrogen bonds in two tetraalkylammonium dithiobiurea(1–) inclusion compounds

Two inclusion compounds of dithiobiurea and tetrapropylammonium and tetrabutylammonium are characterized and reported, namely tetrapropylammonium carbamothioyl(carbamothioylamino)azanide, C₁₂H₂₈N⁺·C₂H₅N₄S₂⁻, (1), and tetrabutylammonium carbamothioyl(carbamothioylamino)azanide, C₁₆H₃₆N⁺·C₂H₅N₄S₂⁻, (2). The results show that in (1), the dithiobiurea anion forms a dimer via N—H...N hydrogen bonds and the dimers are connected into wide hydrogen‐bonded ribbons. The guest tetrapropylammonium cation changes its character to become the host molecule, generating pseudo‐channels containing the aforementioned ribbons by C—H...S contacts, yielding the three‐dimensional network structure. In comparison, in (2), the dithiobiurea anions are linked via N—H...S interactions, producing one‐dimensional chains which pack to generate two‐dimensional hydrogen‐bonded layers. These layers accommodate the guest tetrabutylammonium cations, resulting in a sandwich‐like layer structure with host–guest C—H...S contacts.     

One barbiturate and two solvated thiobarbiturates containing the triply hydrogen‐bonded ADA/DAD synthon,plus one ansolvate and three solvates of their coformer 2,4‐diaminopyrimidine

A path to new synthons for application in crystal engineering is the replacement of a strong hydrogen‐bond acceptor, like a C=O group, with a weaker acceptor, like a C=S group, in doubly or triply hydrogen‐bonded synthons. For instance, if the C=O group at the 2‐position of barbituric acid is changed into a C=S group, 2‐thiobarbituric acid is obtained. Each of the compounds comprises two ADA hydrogen‐bonding sites (D = donor and A = acceptor). We report the results of cocrystallization experiments of barbituric acid and 2‐thiobarbituric acid, respectively, with 2,4‐diaminopyrimidine, which contains a complementary DAD hydrogen‐bonding site and is therefore capable of forming an ADA/DAD synthon with barbituric acid and 2‐thiobarbituric acid. In addition, pure 2,4‐diaminopyrimidine was crystallized in order to study its preferred hydrogen‐bonding motifs. The experiments yielded one ansolvate of 2,4‐diaminopyrimidine (pyrimidine‐2,4‐diamine, DAPY), C₄H₆N₄, (I), three solvates of DAPY, namely 2,4‐diaminopyrimidine–1,4‐dioxane (2/1), 2C₄H₆N₄·C₄H₈O₂, (II), 2,4‐diaminopyrimidine–N,N‐dimethylacetamide (1/1), C₄H₆N₄·C₄H₉NO, (III), and 2,4‐diaminopyrimidine–1‐methylpyrrolidin‐2‐one (1/1), C₄H₆N₄·C₅H₉NO, (IV), one salt of barbituric acid, viz. 2,4‐diaminopyrimidinium barbiturate (barbiturate is 2,4,6‐trioxopyrimidin‐5‐ide), C₄H₇N₄⁺·C₄H₃N₂O₃⁻, (V), and two solvated salts of 2‐thiobarbituric acid, viz. 2,4‐diaminopyrimidinium 2‐thiobarbiturate–N,N‐dimethylformamide (1/2) (2‐thiobarbiturate is 4,6‐dioxo‐2‐sulfanylidenepyrimidin‐5‐ide), C₄H₇N₄⁺·C₄H₃N₂O₂S⁻·2C₃H₇NO, (VI), and 2,4‐diaminopyrimidinium 2‐thiobarbiturate–N,N‐dimethylacetamide (1/2), C₄H₇N₄⁺·C₄H₃N₂O₂S⁻·2C₄H₉NO, (VII). The ADA/DAD synthon was succesfully formed in the salt of barbituric acid, i.e. (V), as well as in the salts of 2‐thiobarbituric acid, i.e. (VI) and (VII). In the crystal structures of 2,4‐diaminopyrimidine, i.e. (I)–(IV), R₂²(8) N—H…N hydrogen‐bond motifs are preferred and, in two structures, additional R₃²(8) patterns were observed.     

Collisional activation study of cyclic polysulfides

Cyclic polysulfides isolated from higher plants, model compounds and their electron impact induced fragment ions have been investigated by various mass spectrometric methods. These species represent three sets of sulfur compounds: C₃H₆S_x (x=1?6), C₂H₄S_x (x=1?5) and CH₂S_x (x=1?4). Three general fragmentation mechanisms are discussed using metastable transitions: (1) the unimolecular loss of structural parts (CH₂S, CH₂ and S_x); (2) fragmentations which involve ring opening reactions, hydrogen migrations and recyclizations of the product ions ([M? CH₃]⁺, [M? CH₃S]⁺, [M? SH]⁺ and [M? CS₂]^+˙); and (3) complete rearrangements preceding the fragmentations ([M? S₂H]⁺ and [M? C₂H₄]^+˙). The cyclic structures of [M]^+˙ and of specific fragment ions have been investigated by comparing the collisional activation spectra of model ions. On the basis of these results the cyclic ions decompose via linear intermediates and then recyclizations of the product ions occur. The stabilities of the fragment ions have been determined by electron efficiency vs electron energy curves.     

Two salts of 5‐sulfosalicylic acid and 3‐aminopyridine

5‐Sulfosalicylic acid (5‐SSA) and 3‐aminopyridine (3‐APy) crystallize in the same solvent system, resulting in two kinds of 1:1 proton‐transfer organic adduct, namely 3‐aminopyridinium 3‐carboxy‐4‐hydroxybenzenesulfonate monohydrate, C₅H₇N₂⁺·C₇H₅O₆S⁻·H₂O or 3‐APy·5‐SSA·H₂O, (I), and the anhydrous adduct, C₅H₇N₂⁺·C₇H₅O₆S⁻ or 3‐APy·5‐SSA, (II). Both compounds have extensively hydrogen‐bonded three‐dimensional layered polymer structures, with interlayer homo‐ and heterogeneous π–π interactions in (I) and (II), respectively.     

Mass spectral behavior of n-alkynes

The 70 e V-electron impact mass spectra of the C₇–C₁₀ n-alkynes have been determined as well as the metastable ion spectra of the molecular ions and the [CS₂]⁺ and [N₂O]⁺ charge exchange mass spectra of the C₇-C₉ n-alkynes. The metastable ion mass spectra provide only a limited opportunity to distinguish between isomers; however, the 70-eV EI mass spectra of isomeric compounds permit a ready distinction between isomers. The [CS₂]⁺ charge exchange mass spectra of isomeric compounds also show substantial differences. The [N₂O]⁺ charge exchange mass spectra do not show the enhancement of β-fission fragments observed in field ionization experiments, despite representing ions of similar internal energy, and it is concluded that field dissociation is responsible for the β-fission fragments in the field ionization experiments.     

Chemical ionization mass spectra of selected C3H6O compounds

The chemical ionization mass spectra of five isomers of C₃H₆O (acetone, propionaldehyde, oxetane, propylene oxide and allyl alcohol) have been determined using a variety of reagent gases (H₂, D₂, N₂/H₂, CO₂/H₂ and CO/H₂). The [C₃H₇O]⁺ ions produced by protonation of these isomers undergo very similar reactions to those reported for analogous [C₃H₇O]⁺ metastable ions; however, decomposing ions generated by chemical ionization appear to have somewhat higher internal energies. The results of ²H labelling studies (D₂ reagent gas or labelled analogues of C₃H₆O) indicate that protonation occurs mainly on oxygen and are consistent with previous investigations of metastable oxonium ions. The protonated acetone ion is particularly stable, in agreement with the higher activation energies for fragmentation of this isomer than for other [C₃H₇O]⁺ structures. As the calculated heat of protonation of C₃H₆O is reduced by changing the reagent gas, so the extent to which fragmentation occurs decreases. This is discussed in the context of competition between fragmentation and collisional stabilization of the excited [C₃H₇O]⁺* ion. It is concluded that on average a large fraction (approaching 1) of the exothermicity of the protonation reaction resides in the [C₃H₇O]⁺* ions produced initially.     

Different supramolecular assemblies in two 1:1 proton‐transfer compounds of sulfobenzoic acids with aromatic amines

Two 1:1 proton‐transfer complexes of sulfobenzoic acids with aromatic amines, namely 4‐[2‐(4‐pyridyl)ethenyl]pyridinium 2‐carboxybenzenesulfonate, C₁₂H₁₁N₂⁺·C₇H₅O₅S⁻, (I), and 1,10‐phenanthrolin‐1‐ium 4‐carboxybenzenesulfonate dihydrate, C₁₂H₉N₂⁺·C₇H₅O₅S⁻·2H₂O, (II), have very different hydrogen‐bonding patterns compared with reported organic sulfobenzoic acid complexes. In (I), two cations and two anions form a four‐molecule loop, in which π–π interactions occur. In (II), the anions and water molecules form a three‐dimensional hydrogen‐bonding network, while the cations only act as pendant components. The water molecules play a central role in the formation of the abundant hydrogen‐bonding architecture in (II). The relative poorness and richness of hydrogen bonds in (I) and (II), respectively, give rise to novel hydrogen‐bonding patterns.     

Three rotational isomers of se-methyl N,N-di-isopropyldiselenocarbamate and the sulphur analogue found in low temperature 1H NMR spectra

Variable temperature ¹H NMR spectra of Se-methyl N,N-di-isopropyldiselenocarbamate, CH₃SeC(Se)N (C₃H₇-i)₂, in CS₂ have indicated that internal rotations around both the carbamate C? N and isopropyl–nitrogen bonds are restricted below ?40°C; the compound exists as three rotational isomers with respect to the isopropyl-nitrogen bond with mol ratios of approximately 0·54:0·31 :0·15. The corresponding dithiocarbamate, CH₃SC(S)N(C₃H₇-i)₂, has also been found to exist as three isomers with ratios of about 0·71:0·27:0·02 under similar conditions. Possible conformations of both carbamate esters are proposed, together with the assignments of each proton signal.     

Dihydrogen Catalysis of the Reversible Formation and Cleavage of CH and NH Bonds of Aminopyridinate Ligands Bound to (η5‐C5Me5)IrIII

This study focuses on a series of cationic complexes of iridium that contain aminopyridinate (Ap) ligands bound to an (η⁵‐C₅Me₅)Ir^III fragment. The new complexes have the chemical composition [Ir(Ap)(η⁵‐C₅Me₅)]⁺, exist in the form of two isomers ( 1⁺ and 2⁺ ) and were isolated as salts of the BAr_F^? anion (BAr_F=B[3,5‐(CF₃)₂C₆H₃]₄). Four Ap ligands that differ in the nature of their bulky aryl substituents at the amido nitrogen atom and pyridinic ring were employed. In the presence of H₂, the electrophilicity of the Ir^III centre of these complexes allows for a reversible prototropic rearrangement that changes the nature and coordination mode of the aminopyridinate ligand between the well‐known κ²‐N,N′‐bidentate binding in 1⁺ and the unprecedented κ‐N,η³‐pseudo‐allyl‐coordination mode in isomers 2⁺ through activation of a benzylic C?H bond and formal proton transfer to the amido nitrogen atom. Experimental and computational studies evidence that the overall rearrangement, which entails reversible formation and cleavage of H?H, C?H and N?H bonds, is catalysed by dihydrogen under homogeneous conditions.     

Supramolecular association in proton‐transfer adducts containing benzamidinium cations. I. Four molecular salts with uracil derivatives

Four organic salts, namely benzamidinidium orotate (2,6‐dioxo‐1,2,3,6‐tetrahydropyrimidine‐4‐carboxylate) hemihydrate, C₇H₉N₂⁺·C₅H₃N₂O₄⁻·0.5H₂O (BenzamH⁺·Or⁻), (I), benzamidinium isoorotate (2,4‐dioxo‐1,2,3,4‐tetrahydropyrimidine‐5‐carboxylate) trihydrate, C₇H₉N₂⁺·C₅H₃N₂O₄⁻·3H₂O (BenzamH⁺·Isor⁻), (II), benzamidinium diliturate (5‐nitro‐2,6‐dioxo‐1,2,3,6‐tetrahydropyrimidin‐4‐olate) dihydrate, C₇H₉N₂⁺·C₄H₂N₃O₅⁻·2H₂O (BenzamH⁺·Dil⁻), (III), and benzamidinium 5‐nitrouracilate (5‐nitro‐2,4‐dioxo‐1,2,3,4‐tetrahydropyrimidin‐1‐ide), C₇H₉N₂⁺·C₄H₂N₃O₄⁻ (BenzamH⁺·Nit⁻), (IV), have been synthesized by a reaction between benzamidine (benzenecarboximidamide or Benzam) and the appropriate carboxylic acid. Proton transfer occurs to the benzamidine imino N atom. In all four acid–base adducts, the asymmetric unit consists of one tautomeric aminooxo anion (Or⁻, Isor⁻, Dil⁻ and Nit⁻) and one monoprotonated benzamidinium cation (BenzamH⁺), plus one‐half (which lies across a twofold axis), three and two solvent water molecules in (I), (II) and (III), respectively. Due to the presence of protonated benzamidine, these acid–base complexes form supramolecular synthons characterized by N⁺—H...O⁻ and N⁺—H...N⁻ (±)‐charge‐assisted hydrogen bonds (CAHB).