Ethers fragmentation mass

The electron ionization (El) mass spectra of TMS ethers and esters are generally characterised by weak or absent molecular ions. The [M—15]+ ion formed by loss of a methyl radical is generally abundant and in the case of alcoholic functions, the loss of a trimethylsilanol molecule [M—90]+ is also diagnostic. The peak at mJz 73, corresponding to the TMS group, is important in nearly all the TMS-derivative mass spectra. Figure 8.2 shows the fragmentation of TMS esters and ethers in mass spectrometric analyses. 

Iron carbonyls may be identified by electron diffraction and x-ray analysis. Also, its solutions in appropriate organic solvents, such as ether, methanol, or acetone may be analyzed by GC/MS. The characteristic mass spectra should indicate the molecular ions corresponding to the carbonyl as well as the mass spectra of CO and Fe(CO)n, where n is the number of CO units in the fragmented mass ions. Flame- or furnace-AA or ICP/AES analysis may be apphed on the nitric acid extract of the compound(s) after appropriate dilution to determine the concentration of iron (See Iron). 

Mass Units of Characteristic Fragment-ions A-G Used for the Identification of Natural, N,O-Acylated Sialic Acids, and of the C7 and C8 Analogs of Neu5Ac and Neu5Gc as their Methyl Esters, Trimethylsilyl Ethers, by Mass Spectrometry"... 

J.P. Morizur, C. Djerassi, Mass spectrometric fragmentation of unsaturated ethers, Org. Mass Spectrom. 1971,5, 895. 

Radula species contain many bibenzyls incorporating prenyl groups. Seven such bibenzyls (612—614,616—618,620) have been isolated from R. variabilis structures were established mainly by detailed analysis of H-NMR and mass spectra (58, 61). In (612) the presence and the location of two phenolic hydroxyls and the geranyl group were settled by comparison of the signal pattern of the aliphatic protons with those of geraniol (3) and by observation of a NOE between two aromatic protons (H-2 and H-6) and the benzylic protons (5 2.93 ppm) of the dimethyl ether. Fragment ions at mjz 91 (100%) and mjz 111 (98%) and formation of a chromane derivative (653) from (612) further supported the proposed structure (612) (Scheme 74). 

Blanchette, M.C. Holmes, J.L. Lossing, F.P. The Fragmentation of Ionized Alkyl Phenyl Ethers. Org. Mass Spectrom. 1989,24,673-678. 

The force field parameters for simulation of amphiphilic fatty ollgoethers obtained from the quanmm mechanics calculations were tested by comparing a computed set of thermodynamic properties with available experimental data. In the current study the validity of the parameters was demonstrated with atomistic MD simulations of diethyl ether (M(CH3)) in gas and liquid phase and in aqueous solution. The gas phase was represented by one molecule M(CH3) in vacuum. The liquid was modeled with 144 molecules of diethyl ether randomly distributed in a cubic periodic box. The dimensions of the box were chosen to ensure mass density of the liquid close to the experimental value at the same temperature - 0.714g/cm. The solution comprised one M(CH3) molecule immersed in a sufficient amount of water. Both the liquid and the solution were simulated by placing the repeating units in periodic boundary conditions. All simulations were performed with the force field parm 99 [21] appended with the derived MM parameters for the ether fragment in NPT ensemble at 300 K and 1 atm for the periodic calculations. The Berendsen method [22] was applied for the temperature and pressure couplings. 

There is another oxygen-stabilized cation of mIz 87 capable of being formed by fragmentation of the molecular ion in the mass spectrum of sec-butyl ethyl ether. Suggest a reasonable structure for this ion. 

There has as yet been no systematic work on the mass spectra of cyclic hydroxamic acids, but from the limited information available the direct loss of 0 or OH from the molecular ion is to be expected. The fragmentation behavior of the 0-alkyl derivatives is rather unpredictable, although again processes involving fission of the N—0 bond are generally important. Table II shows the prominent first-generation fragment ions from a few hydroxamic acids and their ethers. 

Fragmentation Losses of 1(H), 28 (CO), and 29 (CHO) Daltons are commonly observed for diaryl ethers. In diphenyl ether, m/z 77 is intense, while in phenyl toluoyl ethers m/z 91 is intense, An intense peak in the mass spectra of alkyl phenyl ethers occurs at m/z 94. 

Fragmentation Losses from the molecular ions are 1, 29, and 30 Daltons with the loss of 29 (CHO) being characteristic of cyclic ethers. This loss also appears in the mass spectra of unsaturated cyclic ethers, such as furans and benzofurans. The fragmentation of saturated cyclic ethers generally shows a M — 1 ion. 

The reaction products from 2,4-dichlorophenol were tetrachloro-phenoxyphenols and tetrachlorodihydroxybiphenyls (Figure 5), as determined from their mass spectra and those of their methyl ethers. 4,6-Dichloro-2-(2, 4 -dichlorophenoxy)phenol (V) was the major phenoxy-phenol the mass spectral fragmentation pattern of o-hydroxyphenol ethers is quite characteristic since a hydrogen transfer occurs during the fragmentation (Figure 6). A trace of a trichlorophenoxyphenol also was detected and was formed presumably by the unsensitized reductive loss of chlorine, discussed previously. 

The mass spectra of TMS ethers are characterized by weak or absent molecular ions the [M-15] ion formed by cleavage of a methyl to silicon bond is generally more abundant. This ion can be used to determine the molecular weight provided that it is not mistaken for the molecular ion itself. Dissociation of the molecular ion often results in prominent secondary fragment ions containing the ionized dimethylsiloxy group attached to a hydrocarbon portion of the molecule. In common with alkyl ethers,... 

Figure 8.2 Fragmentation of trimethysilyl esters (a) and ethers (b) in mass spectrometric analyses...

The El mass spectra of a,co-dicarboxylic acids and co-hydroxycarboxylic acids are characterised by ions arising from the fragmentation of the TMS ester and ether moieties and from fragmentation due to interactions between the two TMS... 

Neomycin is insufficiently volatile for direct mass spectrometric analysis. To overcome this problem Inouye- - prepared the volatile N-salicylidene Schiff s base, the M.S. of which, however, did not exhibit a peak for the molecular ion. To observe the molecular ion it was necessary to use the o-trimethylsilyl ether of the N-salicylidene Schiff s base. The spectrum of N-salicylidene neomycin was found to be dependant on the ion-chamber temperature indicating that thermal decomposition plays a significant part in the fragmentation process. 

In principle, mass spectrometry is not suitable to differentiate enantiomers. However, mass spectrometry is able to distinguish between diastereomers and has been applied to stereochemical problems in different areas of chemistry. In the field of chiral cluster chemistry, mass spectrometry, sometimes in combination with chiral chromatography, has been extensively applied to studies of proton- and metal-bound clusters, self-recognition processes, cyclodextrin and crown ethers inclusion complexes, carbohydrate complexes, and others. Several excellent reviews on this topic are nowadays available. A survey of the most relevant examples will be given in this section. Most of the studies was based on ion abundance analysis, often coupled with MIKE and CID ion fragmentation on MS " and FT-ICR mass spectrometric instruments, using Cl, MALDI, FAB, and ESI, and atmospheric pressure ionization (API) methods. 

Nazarpack-Kandlousy, N. Nelen, M. I. Goral, V Eliseev, A. V. Synthesis and mass spectrometry studies of branched oxime ether libraries. Mapping the substitution motif via linker stability and fragmentation pattern. J. Org. Chem. 2002, 67, 59-65. 

Osmiumfvi).—The i.r. spectrum of [OsOCl ] has been recorded in the gas and liquid phases, and in solution. While the exact geometry could not be deduced, evidence was obtained for facile co-ordination of acetone or ether to the species in inert solvents. A mass spectral study of this complex reveals a complex fragmentation pattern, including the previously unknown [OsOClj] species. ... 

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