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Protonated ions

Typical Cl processes in which neutral sample molecules (M) react with NH to give either (a) a protonated ion [M + HJ or (b) an adduct ion [M + NHJ+ the quasi-molecular ions are respectively 1 and 18 mass units greater than the true mass (M). In process (c), reagent ions (CjHf) abstract hydrogen, giving a quasi-molecular ion that is 1 mass unit less than M. [Pg.4]

Ionization can be improved in many cases by placing the sample in a matrix formed from sinapic acid, nicotinic acid, or other materials. This variant of laser desorption is known as matrix-assisted laser desorption ionization (MALDI). The vaporized acids transfer protons to sample molecules (M) to produce protonated ions [M + H]+. [Pg.384]

The ablated vapors constitute an aerosol that can be examined using a secondary ionization source. Thus, passing the aerosol into a plasma torch provides an excellent means of ionization, and by such methods isotope patterns or ratios are readily measurable from otherwise intractable materials such as bone or ceramics. If the sample examined is dissolved as a solid solution in a matrix, the rapid expansion of the matrix, often an organic acid, covolatilizes the entrained sample. Proton transfer from the matrix occurs to give protonated molecular ions of the sample. Normally thermally unstable, polar biomolecules such as proteins give good yields of protonated ions. This is the basis of matrix-assisted laser desorption ionization (MALDI). [Pg.399]

Examination of the mass spectrum of P2VPY taken during the maximum decomposition rate reveals the major decomposition products as methylpyridine (93 a.m.u.), protonated vinyl pyridine (106 a.m.u.), and protonated dimer (211 a.m.u.) with ion ratios 74 100 59 respectively. Trimeric and tetrameric protonated species (316 and 421 a.m.u.) are also observed but in relatively small amounts. Protonated ions, rather than the simple monomers and dimers observed for the decomposition of poly(styrene) by MS11, may be created by a mechanism similar to that reported for the decomposition of 2-(4-heptyl)pyridine12 in the mass spectrometer. [Pg.432]

This reaction is analogous to deprotonation reactions of multiply protonated ions by neutral bases B such as ... [Pg.287]

When experiments with electrospray producing H3N(CH2)pNH2+ ions were performed in this laboratory,56 it was found that doubly protonated ions could be obtained from methanol-water solutions only when p > 4. For p < 4 only the singly protonated ions were observed, even though the doubly protonated ions are known to be present in the solution. We attribute the failure to observe the doubly protonated ions with p < 4 to the occurrence of charge reduction by deprotonation. Probably methanol, whose gas-phase basicity is greater than that of water, is involved in the deprotonation. The diprotonated diammines, p > 4, could all be dehydrated down to the naked ion either in CID experiments or at higher temperature. [Pg.288]

The diamines and their mono- and di-protonated ions can exist in various conformations, in which the nitrogen lone pairs and the protons on nitrogen are directed in (i or i+) or directed out (o or o+) from the molecular cavity. Diprotonated l,10-diazabicyclo[8.8.8]hexacosane, for example, may exist in either of the three forms in equation (79). When the out-out isomer of l,10-diazabicyclo[8.8.8]hexacosane bis hydrochloride (o+ o+) is dissolved in aqueous acidic solution, isomerisation to the in-in isomer (i+ i+) occurs so... [Pg.185]

Many matrix molecules are acidic and can produce protons that attach to the gas-phase substrate molecules, producing protonated ions. Metal complexes examined by MALDI should have the ability to be stable in an acidic environment. A study of some metal complexes, by comparing the solid state, solution state, and gas-phase ions produced by MALDI, indicate that preformed species due to reaction of the complexes with the matrix can be predicted on the basis of condensed-phase thermodynamics (67). [Pg.355]

In a recent upsurge of studies on electron transfer kinetics, importance was placed on the outer shell solvent continuum, and the solvent was replaced by an effective model potential or a continuum medium with an effective dielectric constant. Studies in which the electronic and molecular structure of the solvent molecules are explicitly considered are still very rare. No further modem quantum mechanical studies were made to advance the original molecular and quantum mechanical approach of Gurney on electron and proton (ion) transfer reactions at an electrode. [Pg.72]

Since the monoisotopic signal is the protonated ion, the elemental composition for the API in the counterfeit tablets was therefore determined as C8lTj502N7S3. A computerized search of The Merck Index using the elemental formula suggested the unknown compound to be Famotidine, an active pharmaceutical ingredient widely used in over-the-counter antiulcerative medicine. [Pg.562]

It is a well established fact that the preferred site of protonation of aniline in solution is the nitrogen atom, due to the higher stabilization upon solvatation of the N-protonated species with respect to the ring protonated ion (/). In the gas phase however, the situation is less clear, and the preferred site of protonation has been the subject of many experimental and theoretical studies. Based on proton transfer equilibria at 600 K and upon correlation of the proton affinities... [Pg.184]

As has been pointed out in the past (e.g. concerning the linear-cyclic equilibrium in Ceand Cio carbon clusters (40)), Hartree-Fock underestimates the resonance stabilization of aromatic relative to non-aromatic systems (in the case at hand, between the N- and / -protonated isomers) and MP2 overcorrects. The structures are found to be nearly isoenergetic at the CCSD level inclusion of connected triple excitations favors the N-protonated ion. The direction of the effect of connected quadruples is somewhat unclear, and a CCSD(TQ) or CCSDT(Q) calculation impossible on systems this size, but the contribution will anyhow be much smaller in absolute magnitude than that of connected triple excitations, particularly for systems like these which are dominated by a single reference determinant. We may therefore infer that at the full Cl limit, the N-protonated species will be slightly more stable than its / -protonated counterpart. [Pg.188]

These spectral changes are consistent with either (a) freezing out a stable non-classical ion, or (b) the presence of the classical ion in which the 6,2-hydride shift has been slowed down, but the Wagner-Meerwein rearrangement is still exceedingly rapid. If the ion is non-classical, the spectrum indicates that it must be a comer-protonated nortricyclene rather than the edge-protonated ion because the latter would have split into a 1 2 1 pattern. [Pg.212]

Structures of protonated cyclobutanes have been studied in the same fashion (see Figure 9 B). In the corner-protonated cyclobutane, the structure corresponds essentially to a methyl cation interacting with a trimethylene diyl, and is much less favorable than that for cyclopropane. Similarly, for the edge-protonated ion, the proton must come much closer to the carbons to form a bond than for cyclopropane, and as a result, cyclobutane is much less basic. [Pg.13]


See other pages where Protonated ions is mentioned: [Pg.2]    [Pg.5]    [Pg.38]    [Pg.383]    [Pg.138]    [Pg.163]    [Pg.60]    [Pg.10]    [Pg.16]    [Pg.303]    [Pg.313]    [Pg.374]    [Pg.381]    [Pg.167]    [Pg.207]    [Pg.66]    [Pg.125]    [Pg.459]    [Pg.326]    [Pg.521]    [Pg.522]    [Pg.18]    [Pg.5]    [Pg.375]    [Pg.128]    [Pg.257]    [Pg.268]    [Pg.280]    [Pg.171]    [Pg.58]    [Pg.138]    [Pg.405]    [Pg.1086]    [Pg.13]    [Pg.115]    [Pg.134]   
See also in sourсe #XX -- [ Pg.263 ]

See also in sourсe #XX -- [ Pg.75 ]




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A Equilibria between Isomeric Ions Differing in the Site of Proton Attachment

Asymmetric aqueous aza Diels-Alder reaction with simple protonated iminium ions

Carbonium ions isobutane protonation

Carbonium ions protonation

Electron, Proton, and Heavy Ion Bombardments

Enolate ions protonation

Fluxes in a Mixed Proton, Oxygen Ion, and Electron Conductor

Fluxes in a Mixed Proton, Oxygen Ion, and Electron Conductor Revisited

Hydride Ion, Proton and Carbocation Transfer to Monomer

Hydrogen ions Proton

Hydronium ions proton solvation models

Iminium ions, protonated

Ion and proton-transfer

Ion-proton exchange

Metal ions protons and

Negative ions proton transfer

Peptide ions multiply-protonated

Positive ions proton transfer

Potassium ion and protons

Proton (H Ion) Conductors

Proton conduction mechanism hydronium ions

Proton ions

Proton ions

Proton ions and

Proton transport mechanisms oxygen ions

Proton- and ion-transfer reactions

Protonated C-acyl iminium ions

Protonated C-acyl iminium ions as heterodienophiles

Protonated Methane Ions and their Analogs

Protonated molecular ion

Protonation by Hydronium Ion

Protons in ions

Reactivity of Proton at C2 Position in Imidazolium Ion

Simple protonated iminium ions

Simple protonated iminium ions as heterodienophiles

Synthetic applications of the aqueous aza Diels-Alder reaction involving simple protonated iminium ions

Synthetic applications of the aqueous aza Diels-Alder reaction with protonated C-acyl iminium ions

Synthetic applications of the asymmetric aqueous aza Diels-Alder reaction with simple protonated iminium ions

The Proton as a Different Sort of Ion

The hydrogen ion (proton)

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