Ether Ions Research Articles

Gas-phase complexation of polyethers with halide ions

Gas-phase complexes of halide anions with a variety of crown ethers and acyclic analogs are formed by ion-molecule reactions in the chemical ionization source of a triple-quadrupole mass spectrometer. The ether complexes of iodide, bromide, and chloride dissociate on collisional activation by cleavage of the halide-ether electrostatic hydrogen bonds, resulting in the formation of bare halide anions. By contrast, the fluoride complexes dissociate by loss of HF, which may occur in conjunction or sequentially with losses of ethylene oxide units. This dissociation of behavior is similar to that observed for collisionally activated dissociation of [M — H] − ions of the crown ethers and suggests that the fluoride ion is capable of promoting an intramolecular proton abstraction within the [M + F] − complex. This type of dissociation chemistry is only observed for the fluoride ion complexes, and the fluoride ion is the most basic of all the halides. The kinetic method was used to establish orders of relative halide binding strengths, and the trends for the chloride and bromide affinities were 12-crown-4 < triethylene glycol dimethyl ether < 15-crown-5 < tetraethylene glycol dimethyl ether < 18-crown-6 < 21-crown-7 < tetraethylene glycol < pentaethylene glycol < 1,4,7,10,13-pentathiacyclopentadecane.

An investigation of site-selective gas-phase reactions of amino alcohols with dimethyl ether ions

The reactions of dimethyl ether ions with neutral amino alcohols were examined in both a quadrupole ion trap mass spectrometer and a triple quadrupole mass spectrometer. These ion-molecule reactions produced two types of ions: the protonated species [M + 1] + and a more complex product at [M + 13] +. The abundance of the [M + 13] + ions relative to that of the [M + 1] + ions decreases with increasing formal interfunctional distance. Multistage collision-activated dissociation techniques were used to characterize the [M + 13] + product ions, their reactivities, and the mechanisms for their formation and dissociation. In addition, molecular semiempirical calculation methods were used to probe the thermochemistry of these reactions. Reaction at the amino alcohol nitrogen site is favored, and the resulting [M + 13] + addition products may cyclize for additional stabilization. Comparisons were made among the behavior of related compounds, such as alcohols, diols, amines, and diamines. The alcohols reacted only to form the protonated species, but the diols, amines, and diamines all formed significant amounts of [M + 13] + ions or related dissociation products.

Functional group-selective ion-molecule reactions of ethylene glycol and its monomethyl and dimethyl ethers

The selective methylation and methylene substitution reactions of dimethyl ether ions with ethylene glycol, ethylene glycol monomethyl ether, and ethylene glycol dimethyl ether were investigated in a quadrupole ion trap mass spectrometer. Whereas the reactions of ethylene glycol and ethylene glycol monomethyl ether with the methoxymethylene cation 45 + gave only [M + 13] + product ions, the reaction of ethylene glycol dimethyl ether with the same reagent ion yielded exclusively [M + 15] + ions. The relative rates of formation of these products and those from competing reactions were examined and rationalized on the basis of structural and electronic considerations. The heats of formation for various relevant species were estimated by computational methods and showed that the reactions leading to the [M + 13] + ions were more energetically favorable than those leading to the [M + 15] + products for cases in which both reactions are possible. Finally, the collision-induced dissociation behavior of the [M + H] +, [M + 13] +, and [M + 15] + ions indicated that the [M + H] + and [M + 15] + ions dissociated by analogous pathways and were thus structurally similar, whereas the [M + 13] + ions prossessed distinctly different structural characteristics.

Effects of functional group interactions on the bimolecular and dissociation reactions of diols

The influence of functional group interactions on the bimolecular and dissociation reactions of diols were examined in a quadrupole ion trap mass spectrometer. Reactions of dimethyl ether ions with diols resulted in formation of (M + H) + ions and (M + 13) + ions (by net methyne additin). The product distribution depended on the relative separation of the hydroxyl groups within each diol, with the more proximate diols producing the greatest abundance of (M + 13) + ions compared to (M + H) + ions. The enhancement of the formation of (M + 13) + ions is attributed to the capability for electrostatic interactions between the hydroxyl groups and the electropositive methylene group of the methoxymethylene reagent ion. The enhancement is most significant for diols that can adopt five- or to a lesser extent six-membered ring transition states (i.e., any 1,2 or 1,3 diol). Collision-activated dissociation (CAD) techniques, including both sequential activation experiments (MS n ) and comparison of CAD spectra for model compounds, suggest that the (M + 13) + ions are protonated cyclic diethers.

Selective ion-molecule reactions of 2,5-dimethylpyrrole-γ-butyrolactone with dimethyl ether ions

The use of bimolecular reactions as selective and sensitive diagnostic probes of analytically relevant molcules has undergone rapid development, especially with the increasing availability of ion trapping techniques which allow detailed examination of ion-molecule reactions. In this report, selective ion-molecule reactions of 2,5-dimethylpyrrole-γ-butyrolactone with protonated dimethyl ether and methoxymethylene cations (CH3OCH2+) are described. A quadrupole ion trap and a triple-quadrupole mass spectrometer are used to examine the bimolecular and dissociation reactions of γ-butyrolactone and 2,5-dimethylpyrrole, both of which are the building blocks of a more complex bicyclic substrate, 2,5-dimethylpyrrole-γ-butyrolactone. All three compounds are protonated by ion-molecule reactions with dimethyl ether ions. The γ-butyrolactone also reacts with CH3OCH2+ to produce [M + 15]+ ions (by methyl cation attachment), whereas 2,5-dimethylpyrrole reacts to form [M + 13]+ ions (by methylene substitution). The bicyclic substrate reacts with CH3OCH2+ to form only the [M + 13]+ adduct, which indicates that the pyrrole ring mediates the reaction chemistry. By comparing the reactions of model compounds and by using collisional-activated dissociation techniques, the site of the methylene substitution reaction was determined to be a double bond of the pyrrole ring.

Fragmentation of 1- and 3-metroxypropene ions another part of the C 4H 8O + [rad] potential energy surface

The fragmentation mechanisms of metastable ionized 1- and 3-methoxypropene have been examined in detail by using ionization and appearance energy measurements metastable ion and collisional activation mass spectra, and a variety of isotopically labeled molecules. These metastable C 4H 8O + ions fragment by loss of H , CH 3, and H 2CO, and the experimental observations allowed the construction of the potential energy diagram which describes their interconversion and the participation of four other distonic and carbene C 4H 8O + ions. It was found that these two methyl alkenyl ether ions had no common reaction channel with either the 2-methoxy isomer or with any of the alcohol, keto, or enol C 4H 8O + isomers which previously have been extensively studied.

Characterization of the dissociation behavior of gas-phase protonated and methylated lactones

The dissociation behavior of gas-phase protonated and methylated four-, five-, six-, and seven-membered ring lactones, some with methyl substituents in various positions, has been characterized by using a quadrupole ion trap mass spectrometer and a triple quadrupole mass spectrometer. The energy dependence of collisionally activated dissociation pathways was determined by energy-resolved mass spectrometry, and the dissociation behaviour of the various protonated lactones was compared to that observed for protonated cyclic ketones and ethers of analogous ring size. The protonated cyclic ethers and ketones predominantly dissociated via dehydration, whereas the protonated lactones dissociated via losses of an alkene, ketene, and water. The dissociation behavior of the gas-phase methylated lactones formed from ion/molecule reactions with dimethyl ether ions was compared to the collisionally activated dissociation behavior of isomeric protonated methyl-substituted lactones. The methylation experiments indicated that the gas-phase addition of a methyl group may dramatically alter the favored dissociation pathways when compared to the simple protonated ions.

Isotope effects in the dissociation of partially deuterated dimethyl ether, CH 3OCD +3 ions

The dissociation of partially deuterated dimethyl ether ions(CH 3OCD + 3) is studied from the ionization potential of 10.03–16eV photon energy. Ions are produced by photoionization with synchrotron radiation and selected in internal energy by threshold photoelectron—photoion coincidence. Up to 13eV the major fragments correspond to an H or D atom loss by a simple bond cleavage. However, the shift in the H and D loss onsets indicates that there is a small reverse activation energy as a result of the zero point energies in the CX deformation modes. A new value for Δ H° fo(CH 3OCH + 2) of 161.1 kcalmol −1 is derived. The CH 2OH + and CD 2OD + products appear at 11.75 eV, 0.95 eV above their thermochemical onset, and remain minor fragments in the whole energy range studied. No scrambling of the H and D atoms is observed. Modeling of the breakdown graph by RRKM theory indicates that the CX 2OX + (X  H or D) fragments are produced via a 1.35 eV barrier. We observe an isotope effect in both these dissociation channels which is well explained by zero point energy, and density of states differences in the framework of the RRKM calculations. The analysis shows that in the energy range investigated, tunneling is not an important process in the CH 2OH + formation. At 15 and 16 eV photon energies, the main fragments are XCO + and CX + 3 (X  H or D). Non-statistical scrambling of the hydrogen atoms in CX + 3 is observed.

Structures of [C3H6O]+· ions from propylene oxide and methyl‐substituted 1,3‐dioxolanes by photodissociation and ion/molecule reactions

AbstractPhotodissociation experiments and ion/molecule reactions with pyridine and hex‐1‐ene show that [C3H6O]+· ions from propylene oxide isomerize to the vinyl metbyl ether structure. [C3H6O]+· fragment ions from methyl‐substituted 1,3‐dioxolanes have lower internal energies. In these cases a mixture of photodissociating ring‐opened propylene oxide ions and vinyl methyl ether ions is observed.

ChemInform Abstract: Transition Metal Mediated Organic Synthesis: The Synthesis of Moracin M.

AbstractThe halobenzofuran (Ia) is coupled with the tricarbonylchromium metalloarene (IIa) in the presence of Pd(0) to yield the complexed benzofuranylarene (IIIa).

Chemical reactions on clusters. 3. Gas-phase unimolecular decomposition of dimethyl ether(1+) ion [(CH3)2O+] in association with argon clusters

Chemical reactions on clusters. 3. Gas-phase unimolecular decomposition of dimethyl ether(1+) ion [(CH3)2O+] in association with argon clusters

The structure of decomposing [C7H7O]+ ions: Benzyl versus tropylium ion structures

AbstractThe unimolecular dissociation reactions for [C7H7O]+ ions generated by fragmentation of a series of precursor molecules have been investigated. The metastable kinetic energy values and branching ratios associated with decarbonylation and expulsion of a molecule of formaldehyde (CH2O) from the [C7H7O]+ ions are interpreted as the hydroxybenzyl and hydroxytropylium [C7H7O]+ not interconverting to a common structure on the microsecond time‐scale. In addition, similar measurements on protonated benzaldehyde, methylaryloxy and phenyl methylene ether [C7H7O]+ ions are interpreted as the dominant fraction of these decomposing ions having unique structures on the microsecond time‐scale. These results are supported by experimental heats of formation calculated from ionization/appearance energy measurements. The experimental heats of formation are determined as: hydroxybenzyl ions, 735 kJ mol−1; hydroxytropylium ions, 656 kJ mol−1; phenyl methylene ether ions, 640 kJ mol−1; methylaryloxy ions 803 kJ mol−1. The combination of the results reported in this paper with previously reported experimental data for stable [C7H7O]+ ions (see Ref. 1, C. J. Cassady, B. S. Freiser and D. H. Russell, Org. Mass Spectrom.) is interpreted as evidence that the relative population of benzyl versus tropylium [C7H7O]+ ion structures from a given precursor molecule is determined by isomerization of the parent ion and not by structural equilibration of the [C7H7O]+ ion.

Structural determination of [C7H7O]+ ions in the gas phase by ion cyclotron resonance spectrometry

AbstractThe [C7H7O]+ ions from a series of compounds have been studied using ion cyclotron resonance spectrometry. The techniques employed in this gas phase ion structure determination of [C7H7O]+ were photodissociation, ion‐molecule reactions, and collisionally activated dissociation using a Fourier transform mass spectrometer (FTMS‐CAD). In addition to the low energy FTMS‐CAD results, high energy CAD data obtained with a sector mass spectrometer is also provided. Evidence was found for five unique [C7H7O]+ structures, including the hydroxybenzyl ion, the hydroxytropylium ion, the protonated benzaldehyde ion, the methylaryloxy ion and the phenyl methylene ether ion. Ion‐molecule reactions, invovling both proton transfer and methylene transfer, provided the most unambiguous results and yielded qualitative and quantitative evidence for the five structures. However, a combined approach using the three techniques was necessary to identify all of the structures. The tropylium form of [C7H7O]+ was found to absorb strongly at 305 nm, while the protonated benzaldehyde ion was found to have a strong absorption band at 305 nm and a weak band at 370 nm. The proton affinity of 2,4,6‐cycloheptatrienone was determined to be 918±8 kJ mol−1, which is considerably lower than a previously reported value. In addition, deprotonation reactions of the methylaryloxy ion yielded a proton affinity of 871±14 kJ mol−1 for 4‐methylenecyclohexa‐2,6‐diene‐1‐one.

Estrogens in seminal plasma of human and animal species: Identification and quantitative estimation by gas chromatography—Mass spectrometry associated with stable isotope dilution

Estrone, 2-methoxyestrone and estradiol-17β have been definitively identified in seminal plasma of man, bull, boar and stallion by high resolution gas chromatography associated with selective monitoring of characteristic ions of suitable derivatives. Quantitative estimations were performed by isotope dilution with deuterated analogues and by monitoring molecular ions of trimethylsilyl ethers of labelled and unlabelled compounds. Concentrations of unconjugated and total estrogens are reported together with the statistical evaluation of accuracy and precision.

Dadi spectra of gossypol hexamethyl ethers and mixtures of them

The DADI spectra of the M+ ions of hexamethyl ethers of three tautomeric forms of gossypol and of mixtures of them have been studied. A specific fragmentation pathway of M+ for each form has been shown. On the basis of the results obtained, the amounts of the hexamethyl ethers of each tautomeric form produced in the methylation of gossypol have been found.

A selected ion monitoring assay for primaquine in plasma and urine

The antimalarial drug primaquine was analysed in plasma and urine by gas chromatography mass spectrometry, using a deuterated internal standard. After freeze-drying and extraction with trichloroethylene the sample plus internal standard was reacted with Tri Sil TBT (a 3:3:2 by volume mixture of trimethylsilylimidazole, N,O,-bis-(trimethylsilylacetamide and trimethylchlorosilane) and an aliquot injected into the gas chromatograph mass spectrometer. The gas chromatographic effluent was monitored at m/z 403 and m/z 406, the molecular ions of the bis-TMS ethers of primaquine and 6-trideuteromethoxy primaquine. Calibration curves were prepared from standards made up in plasma and urine. Data from the analysis of plasma and urine samples from a volunteer who ingested the equivalent of 45 mg primaquine are presented.

Origin of the [C4H9O]+ ions in the mass spectrum of n‐butyl ethyl ether

AbstractThe mechanisms of formation of m/z 73 ions in the mass spectrum of the ionized title compound were investigated by deuterium substitution and by examining the decompositions of metastable ions. Two routes to the [C4H9O]+ ions were found in the normal spectrum. The ethyl lost by the major pathway contains the α‐ and β‐hydrogens and a γ‐hydrogen from the butyl group. The minor route involves the loss of ethylene from the [MH]+ ion. There were metastable peaks for losses of ethyl, ethanol and methyl from the molecular ion. The ethyl contains the α‐ and β‐methylenes and a γ‐hydrogen, while the methyl is the δ‐methyl of the butyl group. The labeling data rule out a previous mechanistic proposal for the loss of ethyl and support a mechanism involving stepwise isomerization to the sec‐butyl ethyl ether molecular ion. However, the metastable ion chemistries of the molecular ions from the n‐ and sec‐butyl ethyl ethers are highly dissimilar, perhaps due to decompositions from different electronic states. The n‐pentyl methyl ether ions loses both ethyl and propyl, apparently following rearrangements to the 3‐pentyl and 2‐pentyl ether ions. Di n‐butyl and n‐butyl methyl ethers also give metastable peaks for loss of methyl, ethyl and the shorter chain alcohol.

Crown-cation complex effects. IV. Crown ether and quaternary ion mediated displacements in aryldiazonium compounds

Crown-cation complex effects. IV. Crown ether and quaternary ion mediated displacements in aryldiazonium compounds

Ortho-Effect in some aromatic ethers, sulphides, and sulphoxides under electron impact

An ortho-effect has been found for the loss of Cl· from the molecular ions of chlorodiphenyl ethers, sulphides, and sulphoxides. This was not observed for the corresponding sulphones and o-chlorophenyl benzyl ether, owing to the competition of other, energetically more favourable, reactions. The reaction due to the ortho-effect in the molecular ions of o-chlorodiphenyl ether, sulphide, and sulphoxide were the lowest-energy processes, competing successfully with rearrangements. In the case of the three chlorodiphenyl sulphides, there was indication for a different structure of the ortho-(M– Cl)⌉+ ion from those of the meta- and para-isomers. Chlorine scrambling in simple disubstituted benzenes is discussed in view of the results.