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1.
《Journal of mass spectrometry : JMS》2017,52(4):230-238
Upon activation in the gas phase, protonated benzoic acid (m/z 123) undergoes fragmentation by several mechanisms. In addition to the predictable water loss followed by a CO loss, the m/z 123 ion more intriguingly eliminates a molecule of benzene to generate protonated carbon dioxide (H ‐ O+ ═ C ≡ O , m/z 45), or a molecule of carbon dioxide to yield protonated benzene (m/z 79). Experimental evidence shows that the incipient proton ambulates during the fragmentation processes. For the CO2 or benzene loss, protonated benzoic acid transfers the charge‐imparting proton initially to the ortho position and then to the ipso position to generate a transient species which dissociates to form an ion‐neutral complex between benzene and protonated CO2. The formation of the m/z 45 ion is not a phenomenon unique to benzoic acid: spectra from protonated isophthalic acid, terephthalic acid, trans‐cinnamic acid and some aliphatic acids also displayed a peak for m/z 45. However, the m/z 45 peak is structurally diagnostic only for certain benzene polycarboxylic acids because the spectra of compounds with two carboxyl groups on adjacent ring carbons do not produce a peak at m/z 45. For the m/z 79 ion to be formed, an intramolecular reaction should take place in which protonated CO2 within the ion‐neutral complex acts as the attacking electrophile to transfer a proton to benzene. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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《Journal of Photochemistry》1980,12(2):133-138
The liquid phase photolysis of 1,4-dibromo-2,3-butanedione ((CH2-BrCO)2) was investigated at different wavelengths and in various solvents. In ethanol the major products are CH3COCOCH2Br, CH3CH(OC2H5)2, CH3-COOC2H5 and CH2BrCOOC2H5. Of these compounds only CH3COCOCH2Br is a primary photolysis product originating via hydrogen atom abstraction from CH3CH2OH by the excited (CH2BrCO)2 molecule. The CH3CHOH radical thus formed is the probable precursor of CH3CH(OC2H5)2. It is suggested that the observed esters, which are formed in a 1:1 ratio, are produced by the photolysis of the α-oxo-hemiacetal which is formed by the reaction of (CH2BrCO)2 with ethanol. 相似文献
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Thomas H. Hester Kendra K. McCraney Daniel E. Castillo Daniel J. Goebbert 《Journal of mass spectrometry : JMS》2013,48(4):459-464
Early investigations of protonated polyethylene glycol fragmentation suggested the dissociation mechanism includes both direct and sequential processes. Experiments designed to study the proposed mechanisms of sequential dissociation are absent from the literature. In order to obtain additional experimental details about the fragmentation reactions, the dissociation of protonated polyethylene glycol was studied by energy‐dependent collision‐induced dissociation (CID). Key fragment ions were separated by mass differences corresponding to the loss of single monomer units. Several fragment ions were also generated by in‐source fragmentation and studied by CID. These experiments indicate the primary ions undergo sequential dissociation by the loss of either one or two monomer units. The results suggest that at least two different mechanisms must be considered to explain the sequential dissociation of protonated polyethylene glycols. The reaction involving the elimination of two subunits suggests the loss of a six‐membered 1,4‐dioxane product, while the elimination of a single subunit involves the loss of acetaldehyde by a 1,2‐hydride shift rearrangement. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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L. A. Kochergina A. I. Lytkin O. N. Krutova K. V. Damrina 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2014,88(3):409-412
Heat effects of the dissolution of crystalline L-glutamine in water and lithium hydroxide solutions were determined by direct calorimetry at 298.15 K. Standard enthalpies of formation of L-glutamine and the products of its dissociation in aqueous solution were calculated. 相似文献
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Biacetyl reacts with oxone to give bis-dioxirane [3,3'-dimethyl-3,3'-bidioxirane, 3B] and mono-dioxirane [1-(3-methyl-dioxiran-3-yl)ethanone, 3A)]. Bis-dioxirane 3B is formed when two oxygens are incorporated into biacetyl, while mono-dioxirane 3A incorporated only one. A greater stability is observed in 3B compared to 3A, which is attributed to an alpha-dioxiranyl (anomeric) effect in the former. In contrast, 3A suffers from a destabilizing pi-electron withdrawing effect from the adjacent carbonyl group. 相似文献
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Hydrogen-bond-assisted molecular aggregation of decavanadate anions, [H(n)V(10)O(28)]((6-n)-), in non-aqueous solutions was probed by systematic small-angle X-ray scattering and (1)H and (51)V NMR spectroscopic measurements in mixtures of acetone and 1,4-dioxane. Under acetone-rich conditions, the decavanadate anion prefers a self-associated hydrogen-bonded dimer of {[H(3)V(10)O(28)](2)}(6-), which dissociates into monomeric species as the proportion of 1,4-dioxane increases. The association/dissociation behaviors of the decavanadate anions were proven to be reversible and driven by the protophobic/protophilic nature of the solvent. 相似文献
8.
The standard gaseous enthalpy of formation for methyl fluoride is estimated by five methods, all of which are in remarkable agreement with each other and which deviate significantly from the available experimental values. The suggested derived value is 225.4±3.2 kJ/mol. 相似文献
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Sodium salts of 2,3-quinoxalinedithiol have been prepared and used for determination of the acid ionization constants by potentiometric titration. The fully protonated form of the reagent was used in an alternative determination of the first ionization constant by a solubility method. The constants are pK(2), == 6.84 +/- 0.04 and pK(2) = 9.95 +/- 0.03. 相似文献
11.
Michaux C Wouters J Perpète EA Jacquemin D 《The journal of physical chemistry. B》2008,112(32):9896-9902
The microsolvation of protonated l-alanine with one, two, or three water molecules has been investigated using a MP2/6-311++G(d,p) approach fully accounting for the basis set superposition errors. A conformational analysis for unhydrated AlaH(+) reveals only three minima which have been characterized and compared to the neutral case. We have built a logical tree for the successive hydration stages. This tree shows that the most stable complexes in each step are related and that a systematic approach can be used to grasp the stepwise hydration process. The addition of extra water molecules to the first or second solvation shells leads to the opposite evolution of the hydrogen-bond stretching mode. Comparisons with experimental enthalpies, entropies, and Gibbs free energies clearly demonstrate the adequacy of the approach. Our results also strongly suggest that several di- and trihydrated complexes should coexist under the experimental conditions. 相似文献
12.
L. P. Ogorodova L. V. Mel’chakova I. A. Kiseleva T. N. Shuriga O. V. Kononov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(3):346-349
A thermochemical study of lithium siderophyllite (K0.75Na0.06Rb0.01Ca0.11)(Li0.11Fe 1.25 2+ Mn0.02Mg0.66Al0.35Fe 0.23 3+ Ti0.18)[Si2.53Al1.47O10](OH)1.63F0.37 (I) and siderophyllite (Al-Fe biotite) (K0.89Na0.04)(Fe 1.69 2+ Mn0.03Mg0.20Al0.59Fe 0.14 3+ Ti0.06)[Si2.80Al1.20O10](OH)0.80F1.16Cl0.04(II) was performed on a high-temperature Tian-Calvet microcalorimeter. Their enthalpies of formation from the elements, Δf H el ° (298.15 K) = ?5724 ± 12 (I) and ?5573 ± 14 (II) kJ/mol, were determined by melt solution calorimetry. The Δf G el ° (298.15 K) = ?5359 ± 12 (I) and ?5231 ± 14 (II) kJ/mol values were calculated. An increase in the content of iron in siderophyllite increased the entropy, enthalpy, and free energy of formation from the elements. 相似文献
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The enthalpy of hydrolysis of solid tungsten thiotetrafluoride, WF(in4)S, in aqueous sodium hydroxide solution is -528.2 kJ mo1-1. Hence its standard enthalpy of formation has been calculated to be -1150.5 kJ mo1-1. 相似文献
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Philippe Meyrant Robert Flammang Andr Maquestiau Eric E. Kingston John H. Beynon Joachim G. Liehr 《Journal of mass spectrometry : JMS》1985,20(7):479-482
A series of phenyl ethers with cyclic and acyclic olefins has been observed to form proton-bound complexes on protonation under chemical ionization conditions with methane as the reagent gas. The competitive dissociations of these complexes have been studied by ion kinetic energy spectrometry and the measured branching ratios have been correlated with the relative stabilities of the product species. 相似文献
18.
Sleno L Volmer DA Kovacević B Maksić ZB 《Journal of the American Society for Mass Spectrometry》2004,15(4):462-477
The aim of this study was to investigate the behavior of the protonated paralytic shellfish poisons saxitoxin (STX) and neosaxitoxin (NEO) in the gas-phase after ion activation using different tandem mass spectrometry techniques. STX and NEO belong to a group of neurotoxins produced by several strains of marine dinoflagellates. Their chemical structures are based on a tetrahydropurine skeleton to which a 5-membered ring is fused. STX and NEO only vary in their substituent at N-1, with STX carrying hydrogen and NEO having a hydroxyl group at this position. The collision-induced dissociation (CID) spectra exhibited an unusually rich variety and abundance of species due to the large number of functional groups within the small skeletal structures. Starting with triple-quadrupole CID spectra as templates, linked ion-trap MSn data were added to provide tentative dissociation schemes. Subsequent high-resolution FTICR experiments gave exact mass data for product ions formed via infrared multiphoton dissociation (IRMPD) from which elemental formulas were derived. Calculations of proton affinities of STX and NEO suggested that protonation took place at the guanidinium group in the pyrimidine ring for both molecules. Most of the observed parallel and consecutive fragmentations could be rationalized through neutral losses of H2O, NH3, CO, CO2, CH2O and different isocyanate, ketenimine and diimine species, many of which were similar for STX and NEO. Several exceptions, however, were noted and differences could be readily correlated with reactions involving NEO's additional hydroxyl group. A few interesting variations between CID and IRMPD spectra are also highlighted in this paper. 相似文献
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V. A. Lukyanova T. S. Papina K. V. Didenko A. S. Alikhanyan 《Journal of Thermal Analysis and Calorimetry》2008,92(3):743-746
The standard enthalpy of combustion of crystalline silver pivalate, (CH3)3CC(O)OAg (AgPiv), was determined in an isoperibolic calorimeter with a self-sealing steel bomb, Δc
H
0 (AgPiv, cr)= −2786.9±5.6 kJ mol−1. The value of standard enthalpy of formation was derived for crystalline state: Δf
H
0(AgPiv,cr)= −466.9±5.6 kJ mol−1. Using the enthalpy of sublimation, measured earlier, the enthalpy of formation of gaseous dimer was obtained: Δf
H
0(Ag2Piv2,g)= −787±14 kJ mol−1. The enthalpy of reaction (CH3)3CC(O)OAg(cr)=Ag(cr)+(CH3)3CC(O)O.(g) was estimated, Δr
H
0=202 kJ mol−1. 相似文献
20.
The enthalpy of hydrolysis of solid tungsten azide pentafluoride in alkaline aqueous solution (1.O mol dm?3 KOH; 298.2K) is ?578 kJ mol?1. Hence its enthalpy of formation is ?1170 kJ mol?1. 相似文献