Mass spectrometry of thio analogues of pyrimidine bases: 2-alkoxycarbonylalkyl-thiouracils

The mass spectral fragmentation of twelve new 2-alkoxycarbonylalkylthio substituted derivatives of uracils is discussed and fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions are proposed. It has been found that the basic mass spectral fragmentation of these compounds is due to cleavage of S? C, O? C and C? C bonds of the alkoxycarbonylalkylthio group.     

The activation energy of the skeletal isomerization in the radical cations of toluene and cycloheptatriene by mass spectrometry of their 2-phenylethyl derivatives

The Unimolecular mass spectrometric fragmentations of the molecular ions of 1,3-diphenylpropane, 1-(7-cycloheptatrienyl)-2-phenylethane and the 1-phenyl-2-tolylethanes and their [d₅]phenyl analogues have been investigated by metastable ion techniques and measurements of ionization and appearance energies. By comparing the formation of [C₇H₇]⁺, [C₇H₈]⁺?, [C₈H₈]⁺? and [C₈H₉]⁺ it is shown that the molecular ions of the four diaryl isomers do not undergo ring expansion reactions of the aromatic nuclei prior to these fragmentations. Conversely, the molecular ions of the cycloheptatrienyl isomer suffer in part a contraction of the 7-membered ring. From these results and from the measured ionization and appearance energies lower limits to the activation energies of these skeletal isomerizations have been estimated yielding E > 33±5 kcal mol^?1 formonoalkylbenzene, E > 20 2±5 kc mol^?1 for 7-alkylcycloheptatriene and E > 40±5 kcal mol^?1 for dialkylvbenzene positive radical ions. Upper limits can be deduced from literature evidence yielding E < 45 kcal mol^?1 for monoalkylbenzene and E < 53 kcal 4mol^?1 for dialkylbenzene positive radical ions. The activation energy thus estimated for monoalkylbenzene is in excellent agreement with the recently calculated value(s) for the toluene ion.     

Formation and collision-induced dissociation behaviour of doubly charged gas-phase fullerene anions C,C and higher homologues. Collision-induced electron-stripping process

Doubly charged molecular anions M^2? of fullerenes are formed in the gas phase under chemical ionization conditions with isobutane as the reagent gas. The efficiency of double electron attachment increases with increasing size of the fullerenes: the C ion is the most abundant doubly charged anion in the negative-ion CI mass spectrum, although the concentration of C₇₀ was about 12% in the fullerene mixture examined. Under low-energy collision-induced dissociation conditions an electron is ejected from the doubly charged C ion resulting in the singly charged molecular anion C˙. This process appears to be the first report of the ejection of an electron (electron stripping) from a doubly charged anion in the gas phase: .     

Methylene radical cation transfer from ionized oxirane to CH3SCH3 and C6H5SCH3 in the gas phase: Formation of sulphur distonic ions and/or insertion in a carbon–sulphur bond

The α-distonic sulphur-containing ion $ {}^ \cdot {\rm CH}_2 \mathop {\rm S}\limits^ + \left({{\rm CH}_3 } \right)_2 $ has been generated by transfer of CH from ionized oxirane to dimethyl thioether and distinguished from the molecular ion of ethyl methyl thioether by collision induced dissociation (CID) experiments. In particular, the α-distonic ion expels CH₂ to a minor extent following collision, whereas the molecular ion of ethyl methyl thioether does not undergo this reaction. The metastable C₃H₈S^+˙ ions formed by CH transfer to dimethyl thioether and ionization of ethyl methyl thioether decompose by competing losses of CH₃R˙, CH₄ and C₂H₄. The elimination of ethene is taken as evidence for isomerization of the α-distonic ion to the molecular ion of ethyl methyl thioether prior to spontaneous dissociation. Evidence for the formation of stable α-distonic sulphur-containing ions by transfer of CH from ionized oxirane to methyl phenyl thioether has not been obtained. The collision-induced and spontaneous reactions of the ions formed by CH transfer to methyl phenyl thioether indicate that a mixture of the radical cations of CH₃C₆H₄SCH₃, C₆H₅SCH₂CH₃ and C₆H₅CH₂SCH₃ is generated implying that attack on the phenyl group occurs in addition to a formal insertion of a methylene entity in a C? S bond.     

Formation of· CH2CH2CO + and C2H6+· in the metastable decompositions of ionized ethyl formate

The products of the metastable decompositions of ionized ethyl formate (a) are characterized. The loss of water from a produces ^·CH₂CH₂CO⁺, a rarely reported product. Loss of H appears to produce CH₂=CHC(OH). The third decomposition is an unusual formation of C₂H. This work demonstrates that a previous supposition that isomerization to different intermediates is involved in the losses of ethene and of water from a is correct.     

The haloacetyl ions; a thermochemical study

The haloacetyl ions [XCH₂CO⁺], X = Cl, Br, I, have been produced by the dissociative ionization of selected precursor molecules and identified via their fragmentation characteristics. Their heats of formation, Δ, were 708 ± 8, 750 ± 25 and 784 ± 10 kJ mol^?1, respectively, all appreciably above ΔH for [CH₃CO⁺], 653 kJ mol^?1. The effect of halogen substitution α to carbonyl is discussed for neutral molecules and their molecular ions.     

The mechanism of O(3P) atom reaction with ethylene and other simple olefins

Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature under discharge flow conditions by resonance fluorescence spectroscopy of O and H atoms at pressures of 0.08 to 12 torr. The measured total rate constants of these reactions are K = (7.8 ± 0.6)·10^?13cm³s^?1,K = (4.3 ± 0.4) ± 10^?12 cm³ s^?1, K = (1.4 ± 0.4) · 10^?11 cm³ s^?1. The branching ratios of H atom elimination channels were measured for reactions of O atoms with ethylene and propene. No H-atom elimination was found for the reaction of O-atoms with 2-butene. A redistribution of reaction O + C₂ channels with pressure was found. A mechanism of the O + C₂ reaction was proposed and the possibility of its application to other olefins is discussed. On the basis of mechanism the pressure dependence of the total rate constant for reaction O + C₂ was predicted and experimentally confirmed in the pressure range 0.08–1.46 torr.     

Thermisches Verhalten und Kristallstruktur von YAl3Cl12

Thermal Behaviour and Crystal Structure of YAl₃Cl₁₂ We determined the thermodynamic data of YAl₃Cl₁₂ ΔH = ?739.9 ± 3 kcal/mol and S = 136.1 ± 4 cal/K · mol by total pressure measurements and ΔH = ?739.1 ± 1.6 kcal/mol by solution calorimetry. Using DTA-investigations we established the phase diagram in the system AlCl₃–YCl₃. The crystal structure was refined on the basis of single crystal data (P3₁ 12; Z = 3; a = 1 046.8(2); c = 1 562.3(3) pm).     

Recommendations for measuring second-order rate constants and kinetic solvent isotope effects on acid-catalyzed reactions

Kinetic solvent isotope effects (KSIE) were measured for the hydrolyses of acetals of benzaldehydes in aqueous solutions covering the pH (pD) range of 1–6. For p-methoxybenzaldehyde diethyl acetal, k/k = 1.8–3.1, depending on the procedure used to calculate the KSIE and on the pH (pD) range used as the basis for k(k). It is shown that this variation is an experimental artifact, and is a characteristic of KSIE measurements in general. It is recommended that k be calculated from a least-squares fit of data to the equation k_obs = k[L⁺], and that the KSIE be reported as k/k. The limitation remains, however, that the KSIE measured for a variety of substances over quite different pH (pD) ranges may not be comparable to more than ?20%. The source of these observations is discussed in terms of small changes in the activity coefficient ratios (a specific salt effect), including the solvent isotope effect on the activity coefficient ratio [eq. (3)].     

On the loss of CH from o-methylbenzaldoxime. Evidence for an ortho assisted oxime→nitrone isomerization

Isomerization of oxime molecular ions into nitrone molecular ions upon electron impact does not generally occur, but it was established with the aid of deuterium labelling that it is essential for loss of CH from o-methylbenzaldoxime.     

Generalized statistical gelation theory

Gel points in random polymerizations of the general type Σ_iRA + Σ_jRB in which A-groups react with A- and B-groups, and B-groups react only with A-groups are considered. (The symbols Σ_i and Σ_i signify that the A- and B-bearing reactants RA and RB can be mixtures of monomers of different functionalities, denoted generally as f_ai and f_bj.) The usual case of A-groups reacting only with B-groups is a special case of the present theory. The effects of chemical kinetics, the competitive reaction of A- and B-groups, are separated from the generalized statistical condition for gelation. The former are used to define reaction curves and the latter, gelation curves. Both types of curve are represented as p_a as a function of p_b. For a given polymerization, gelation occurs when the reaction curve and the gelation curve intersect. When A-groups react only with B-groups, the gel points are those for the usual type of Σ_iRA + Σ_jRB polymerization, and, in the limit of A-groups only reacting with A-groups, the gel points are those for Σ_iRA self polymerizations.     

Zur Struktur der LiMIIMIIIF6-Verbindungen. Neue Verbindungen mit MIII=In und Ti

On the Structure of LiM^IIM^IIIF₆ Compounds. New Compounds with M^III=IN and Ti LiMn^IIInF₆ compounds with M^II = Mg, Mn, Co, Ni, Zn, Cd and Ca crystallize in the Na₂SiF₆ structure. The Ti(III) compound LiMgTiF₆ has trirutile structure, LiMnTiF₆ has Na₂SiF₆ and trirutile structure (H.-T. modification), LiCaTiF₆ and LiCdTiF₆ have Li₂ZrF₆ superstructure. With M^II = Co, Ni and Zn solid solutions trirutile — MF₂(rutile) could be only prepared. The lattice constants of all compounds are reported. For LiMnVF₆ and LiFeGaF₆ too dimorphism Na₂SiF₆ trirutile was observed. In the system LiNiCrF₆ (trirutile) — LiMnCrF₆ (Na₂SiF₆ structure) phase limits of both structures are determined in dependence on the ratio of ionic radii r/r. Magnetic data of the In compounds with M^II = Co and Ni and of the Ti(III) compounds with M^II = Mg, Zn, Mn, just as of α- and β-LiMnVF₆ are also given. The three structures only exist if r reaches from 0.6 to 1.2 Å and r from 0.5 to 0.8 Å. The stability-fields are determined by the ratio of ionic radii r/r_Li, r/r_Li and r/r: trirutile 0.9–1.2, Na₂SiF₆ type 1.2–～1.4 and Li₂ZrF₆ superstructure >1.4. The dependence of rate of ionic radii is explained by the different sharing of MF₆ octahedra.     

Chemical actinometry at 147.0 nm

Hexafluoroacetone (HFA) and O₂ were photolyzed at 147.0 nm to investigate their use in chemical actinometry. The products, CO for the former and O₃ in the latter case, were monitored. For accurate comparison, both of these substances were irradiated by a single light source with two identical reaction cells at 180° to each other. The light intensities I were measured under the same integrated as well as instantaneous photon flux based on ? and ?_CO (quantum yield) as 2 and 1, respectively. Optimum conditions for maximum product yield were 5.0 torr HFA pressure and an O₂ flow rate of 200 ml/min at 1 atm pressure for a 20-minute photolysis period. For light intensity variations between 1.09 × 10¹⁴ and 2.10 × 10¹⁵ photons absorbed/sec, the ratio I/I_HFA was found to be unity. Calibration with the commonly used N₂O actinometer for a ? value of 1.41 showed that I/I_HFA and I/I are unity. Both HFA and O₂ are suitable chemical actinometers at 147.0 nm with ?_CO and ? of 1 and 2, respectively. The light intensity determination in the first case involves the measurement of only one product which is noncondensible at 77°K, whereas wet analysis for O₃, the only product, in the second actinometer is necessary. Both of these determinations are quite simple and are preferable over product analysis in N₂O actiometry, wherein N₂ separation from other noncondensibles at 77°K is required.     

Fourier transform ion cyclotron resonance study of the dehydrogenative polymerization of allene and propyne induced by W+ in the gas phase

A Fourier transform ion cyclotron resonance study of the gas-phase reaction of W⁺ with allene is reported. W⁺ successively dehydrogenates at least nine allene molecules, leading to the formation of a series of WC_3nH ions, with WC₂₇H as the largest product observed after a reaction delay of 40 s. Starting from the third reaction, there is a competition between elimination of H₂ and C₂H₂ at each step. The activation of propyne was also investigated and found to lead to essentially the same sequence as with allene. The reaction of W⁺ with 1,1-d₂-allene and collision-induced dissociation spectra of product ions are used to discuss a plausible mechanism for the formation and structures of some of the species observed.     

The kinetics of the reaction F + H2 → HF + H. A critical review of literature data

Published experimental studies concerning the determination of rate constants for the reaction F + H₂ → HF + H are reviewed critically and conclusions are presented as to the most accurate results available. Based on these results, the recommended Arrhenius expression for the temperature range 190–376 K is k = (1.1 ± 0.1) × 10⁻¹⁰ exp |-(450 ± 50)/T| cm³ molecule⁻¹ s⁻¹, and the recommended value for the rate constant at 298 K is k = (2.43 ± 0.15) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The recommended Arrhenius expression for the reaction F + D₂ → DF + D, for the same temperature range, based on the recommended expression for k and accurate results for the kinetic isotope effect k/k is k = (1.06 ± 0.12) × 10^×10 exp |-(635 ± 55)/T|cm³ molecule⁻¹ s⁻¹, and the recommended value for 298 K is k = (1.25 ± 0.10) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 67–71, 1997.     

Über die Reaktion von Schwefel mit Aminen und Formaldehyd. Eine neue Methode zur Herstellung von Thioformamiden und Dithiocarbamaten

The reaction of sulfur with primary or secondary amines and formaldehyde has been studied. A simple one step process for the preparation of thioformamides (RR′NCHS; R ? H, R′ ? CH₃, C₂H₅; R ? R′ ? CH₃, C₂H₅; R+R′ ? ? (CH₂), ? (CH₂), ? C₂H₄OC₂H) and the amine salts of N, N-dialkyl-dithiocarbamic acids (R₂NCS₂ · H₂NR₂, R ? CH₃, C₂H₅, C₄H₉; R₂ ? ? (CH₂), ? (CH₂), ? C₂H₄OC₂H) is reported. In addition, the isolation of diethylamidosulfoxylic acid, (C₂H₅)₂NSOH · 1/2 H₂O, the first derivative of a new class of compounds, is described. The physical properties and the ¹H-NMR. spectra of the above mentioned compounds are given.     

Thermodynamic Studies on the Complexation Reactions of copper(II) Macrocyclic Tetramine Complexes with Monodentate Ligands: I. RAC-5, 7, 7, 12, 14, 14-Hexamethyl-l, 4, 8, 11-Tetraazacyclotetradecane-Copper(II) (Blue) with-Halide Ions

The possibility of a trigonal bipyramidal structure for [Cu(tet b)X]⁺ (blue) (where X=Cl, Br, I) is supported by the observation of two distinct d-d bands, which are assigned as and d, d_xy→d and d_xz, d_yz→d transitions respectively. The stability constants for the formation of [Cu(tet b)X]⁺ (blue) from [Cu(tet b)]^z+ (blue) and X^? were determined by spectrophotometric method at 25°, 35° and 45°C. The corresponding δH° and δS° values were obtained from the variations of the stability constants between 25° and 45°C     

Schwingungsspektren und Kraftkonstanten der Übergangsreihe O2PF—S2PF— S2P(CH3)

Vibration spectra and force constants of the series O₂PF — S₂PF — S₂P(CH₃). The vibrational spectra of OSPF, S₂PF, S₂PF(CH₃) and S₂P(CN) are reported and discussed with O₂PF and S₂P(CH₃). On the basis of a simplified valence-force-field the force constants are calculated and the bonding relations are discussed. In the ions, f PF is lower than in corresponding molecules. The ionic charge is distributed over nearly all atoms of the ions.     

19F-NMR-spektroskopischer Nachweis und Berechnung der statistischen Bildung der gemischten Clusteranionen [(Mo6BrCl)F]2−, n = 0 – 8

¹⁹F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo₆Br Cl )F ]^2?, n = 0 – 8 The complete system of the innersphere mixed clusters (Mo₆BrCl)⁴⁺ is formed by exchange of innersphere bound Clⁱ against outersphere bound Br^a on tempering the solid [(Mo₆Cl)Br] at 500°C for 16 h. After conversion with conc. HCl into (H₃O)₂[(Mo₆BrCl)Cl] and precipitation of the outer Cl^a with AgBF₄ in ethanol, treatment with tetrabutylammonium(TBA)fluoride yields (TBA)₂ [(Mo₆BrCl)F], a mixture of 22 different species. According to the sets of chemical equivalent fluorine atoms in total 55 ¹⁹F nmr signals are expected, which are really observed in the high resolution 1D-¹⁹F-nmr spectrum. Using increments of chemical shifts, peak intensities and multiplet structures as well as the 2D-¹⁹F/¹⁹F-COSY spectrum the complete and unambiguous assignment of all resonances is achieved. From the measured integral intensities the distribution of the different compounds is determined, revealing statistical formation of the geometrical isomers.     

19F-NMR-spektroskopischer Nachweis und statistische Untersuchung zur Bildung der gemischten Clusteranionen [(Mo6ICl)F]2−, n = 0–7, und Darstellung von (TBA)2[(Mo6I)F]

¹⁹F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo₆I Cl )F ]^2?, n = 0–7, and Preparation of (TBA)₂[(Mo₆I )F ] The octa-μ₃-iodo-hexafluoro-hexamolybdate(2?)ion [(Mo₆I)F]^2? is prepared for the first time. The system of the 21 innersphere mixed clusters (Mo₆ICl)⁴⁺, n = 0–7 is formed by exchange of innersphere bound Clⁱ against outersphere bound I^a on tempering solid [(Mo₆Cl)I] at 400°C. Prolonged tempering leads to increasing average n values of the mixture, which is converted into the tetrabutylammonium salt (TBA)₂[(Mo₆ICl)F]. Using increments of chemical shifts and integral peak intensities the 54 ¹⁹F-nmr signals of the 21 species (compound n = 8 is absent) are assigned and confirmed by the 2 D-¹⁹F/¹⁹F-COSY spectrum. From the measured intensities the distribution of the different compounds is determined and proves significant deviation from statistical occupation, revealing the preference of isomers with iodine atoms occupying edges of the innersphere cube and discrimination of those sharing diagonals of the faces. Moreover all compounds with n = 3 and 4 are present overaverage in comparison to the others.