Electron impact induced intramolecular hydrogen transfer reactions in polymethylene glycol di-p-toluenesulfonates

The mechanisms of formation of the ionized acid and the protonated acid fragments in the electron impact induced fragmentation of the title compounds were investigated. The well known mechanisms of hydrogen transfer through mono- and bicyclic transition states that occur in the molecular ions of carboxylic esters are not the main pathways giving rise to these fragments. The major component of the m/z 172 peak corresponding formally to ionized p-toluenesulfonic acid in fact has a different structure; its formation involves a complex mechanism including a double hydrogen transfer reaction.     

Ammonia chemical ionization mass spectrometry of alcohols: Structural,stereochemical, molecular-size and temperature effects

Ammonia chemical ionization (CI) mass spectra of various open-chain, cyclic and unsaturated C₅- to C₁₀-alcohols were obtained at source temperatures ranging from 60° to 250°C. The reactivity of the ammonia adduct ion MNH and its fragmentation channels are characteristic for substrate structure. Although strongly temperature-dependent, the spectra give nevertheless information on the OH-group environment as well as on the C-skeleton at any source temperature. Primary, secondary and tertiary alcohols as well as allylic and simple olefinic alcohols can be distinguished by their spectra, which show ammonium adduct ions [MNH₄]⁺, adduct dehydrogenation ions [MNH₄-H₂], ammonium substitution ions [MNH₄-H₂O]⁺ and [M-OH]⁺-ions as the main characteristic peaks. Moreover, konfigurational assignments of stereoisomeric alcohols are possible for larger substrate-size and source-temperature ranges than with isobutane CI mass spectrometry. Homologous M NH-ions show molecular-size control of fragmentation and linear MNH-ions are less stable than branched isomers due to incomplete energy randomization.     

Etude par spectrométrie de masse de la fragmentation du désoxy-3-di-O-isopropylidène-1,2: 5,6-méthylidène-3-α-D-hexofurannose et de quelques analogues substitués en C(3′)

Electron Impact Mass Spectrometry of the 3-Desoxy-1,2: 5,6-di-O-isopropylidene-3-methylidene-δ-D -hexofuranose and Some C(3′)-Substituted Analogues The mass spectra of the 3-desoxy-1,2:5, 6-di-O-isopropylidene-3-methylidene- α-D -ribo-hexofuranose and of some C(3′)-mono- and -disubstituted derivatives have been investigated. Deuterium labelled molecules allow fragmentation modes to be proposed.     

The loss of a methyl radical and the retro diels—Alder reaction in the electron impact mass spectrometry of 2-cyclohexen-1-ol and related compounds

The electron impact mass spectra of 2-cyclohexen-1-ol and of several of its ²H and ¹³C labelled analogues show that the molecular ions lose a methyl radical by a completely different means from the mechanism described previously. Moreover, the retro Diels–Alder reaction also proceeds in a non-classical way; in addition to the elimination of an olefinic molecule from unrearranged molecular ions, a second more important route implies a formal 1,3 allylic rearrangement prior to the retro Diels–Alder reaction. The mass spectra of a series of alkyl substituted homologues show that the competition between the two processes is closely related to the size of the olefinic moiety that is expelled.     

Separation of chlorins and carotenoids in capillary electrophoresis

The present study reports the investigation of capillary electrophoresis (CE) for the separation of the photosynthetic pigments (chlorophyll derivatives as well as carotenoids) together. Various CE methods, such as micellar electrokinetic chromatography, capillary electrokinetic chromatography, and nonaqueous capillary electrophoresis (NACE) are tested, with coated and uncoated capillary columns to evaluate optimal separation conditions using diode array detection. The effect of different type and composition of organic solvents and surfactants on the separation is discussed. Detection limits are found in the range of 1.14-2.45 ppm. According to the system suitability results, the most effective separation is observed using NACE with Aliquat 336 as cationic surfactant in coated capillary and mixture of MeOH-ACN-THF (5:4:1, v/v/v) as solvent. Quantitative evolution is investigated, and recovery percentage values are found to be 96.7-102%.     

Influence of the water content of the solvent on the product distribution in the electrohydrodimerization of 2-cyclohexenones

The product distribution of compounds 2 , 3 and 4 formed in the electrohydrodimerization (EHD) of 1 was determined as function of the water content of the solvent (CH₃CN). The presence of water favours the formation of the glycols 4 and reduces the relative amounts of 1,6-diketones 2 and hydroxyketones 3 , as determined by GC./MS.-analysis.     

Characterization of chlorins within a natural chlorin mixture using electrospray/ion trap mass spectrometry

Chlorins in a sedimentary mixture were characterized, without prior isolation of individual components, using electrospray ionization combined with ion trap mass spectrometry. Collision-induced dissociation in the atmospheric sampling interface and multi-step mass spectrometry (i.e. MSⁿ where n ? 2) were used in order to obtain structural information about the macrocycle. Fragmentation pathways are proposed for different macrocycle types based on data from model chlorins. Three unknown chlorins (RMM = 888, 844 and 790) are assigned as having bacteriochlorophyll macrocycle types esterifled to unusual side-chains (i.e. dihydrophytol for the unknown with a bacteriopheophorbide a structure, phytol and an alcohol with a molecular mass of 242 u for the two unknowns with a proposed bacteriopyropheophorbide d structure).     

Etude par Spectrométrie de Masse de la Fragmentation d'une Série de Diols Aliphatiques

The mass spectrometric fragmentation of a series of diols having the general formula HO? (CH₂)_n? OH with n = 2-11 has been studied. Extensive labelling of n-butane-1,4 diol and n-hexane-1,6 diol with deuterium allows fragmentation modes to be proposed. The labelling reveals that intramolecular exchange of H atoms often precedes the fragmentation and becomes more important when the length of the chain increases.     

A CRACK PROBLEM WITH A BROKEN LINE INTERFACE

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