Reaction of ionized propene with methanol: Comparison with CH3OH2+ formation from ionized 2-methylpropanol (original) (raw)
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Journal of Mass Spectrometry, 1995
Proton-transfer reactions that proceed within methanol cluster ions were studied using an electron impact time-offlight mass spectrometer. When CH,OH seeded in helium is expanded and ionized by electron impact, the protonated species, (CH,OH),H+, are the predominant cluster ions in the low-mass region. In CH,OD clusters, both (CH,OD),H+ and (CH,OD),D+ ions are observed. The ion abundance ratios, (CH30D),H+/(CH30D),D+, show a tendency to decrease as the methanol concentration increases, which is apparently related to the cluster structure and reaction energetics. The results suggest that the effective formation of (CH,OD),H+ ions at low concentration of CH,OD in the expansion is the result of the relatively facile rotation of methanol molecules within the smaller clusters that tend to form at low CH,OD concentration. Ab initio molecular orbital calculations were carried out to investigate the rearrangement and dissociative pathways of ionized methanol dimer. Ion-neutral complexes, [CH,OH,+-.O(H)CH,] and [CH,OH,+-OCH,I, are found to play an important role in the lowenergy pathways for production of CH30H2+ + CH,OH (and OCH,) from ionized methanol dimer.
Ion-molecule reactions of fragment ions derived from protonated allyl methyl ether
Organic Mass Spectrometry, 1988
Unusual behaviour has been noted for allyl methyl ether (1) chemically ionized in a high-pressure ion source. Tandem mass spectrometry indicates the formation of methylcyclopentadienyl and methoxy-1-propenylcarbenium ions (d, m/z 81 and e, m/z 85). The origin of these unexpected ions has been elucidated using conventional and Fourier transform ion cyclotron resonance experiments: primary fragment ions derived from protonated 1 (allyl ions a and methoxymethyl cations b) generate collision complexes with neutral 1, giving rise to the ions d and e. respectively, after methanol elimination.
Organic Mass Spectrometry, 1993
Reactions that proceed within mixed ethylenemethanol cluster ions were studied using an electron impact time-offlight mass spectrometer. The ion abundance ratio, [ (C2H,),(CH30H),H+ I/[ (C2H,),(CH30H),+ 1, shows a propensity to increase as the ethylenelmethanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope-labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C,H,),(CH,OH), + and (C,H,),(CH,OH),-,CH,O+ ions are interpreted as a consequence of the ion-neutral complex and intracluster ion-molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C2H4),(CH30H),H+ ions with n + m < 3 have particularly stable structures. The result is unterstood on the basis of ion-molecule condensation reactions, leading to the formation of fragment ions, CH,=OCH, and (CH30H)H30+, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C,H,),(CH,OH),H+(n + m < 3) using semiempirical molecular orbital calculations
International Journal of Mass Spectrometry and Ion Processes, 1992
The tandem flowing afterglow-selected-ion flow tube has been employed to measure rate coefficients and product branching ratios for the reactions of CH,OH: with CH,OH and its various isotopicallylabeled analogs. The branching ratios are approximately 85%, 4%, and 11% for the proton transfer, condensation (S, 2), and association channels respectively. When hidden product channels are accounted for, reaction is found to occur upon every collision. Our results indicate that a proton-bound dimer, in which there is a facile proton transfer, is formed in > 99% of the collisions; this complex can redissociate, undergo collisional stabilization or rearrange to allow S,2 backside displacement and formation of the condensation products. Direct formation of the methyl-bound complex which leads to S,2 reaction without prior formation of a proton-bound dimer is found to be a minor (< 1%) channel. The exchange reaction of C:H,O+ with Dr'sO confirms that the structure of the association product, CH,OH: *CH,OH, is a proton-bound methanol dimer rather than the isomeric proton-bound dimethyl ether-water cluster.
Gas phase reactions of protonated 1,3-diphenylpropyne and some isomeric [C15H13]+ ions
Organic Mass Spectrometry, 1985
Metastable (3-phenyl-2-propynyl)benz611ium ions, generated by electron impact induced fragmentation from the appropriately substituted l,.l-dihydrobenzoic acid, react by loss of 'CH, and C6&. The study of deuterated derivatives reveals that hydrogen/deuterium exchanges involving all hydrogen and deuterium atoms precede the fragmentations. The resdts suggest a skeletal rearrangement by eleebrophilic ring-closnre reactions giving rise to protonated phenylindene and protonated 9,10-methano-9,10-dihydroanthracene prior to the elimination of C6& and 'CH,, respectively. A study of isomeric [C,HJ ions by collision-induced decomposition and by deuterinm labelling shows that these ions interconvert by hydrogen migrations and skeletal rearrangements.
Journal of the American Society for Mass Spectrometry, 1995
The C 3H 60+' ion formed upon the dissociative ionization of 2-methoxyethanol is identified by a combination of several tandem mass spectrometry methods, including metastable ion (MU characteristics, collisionally activated dissociation (CAD), and neutralization-reionization mass spectrometry (NRMS). The experimental data conclusively show that 2methoxyethanol molecular ion, namely, HOCH2CH20CHr, loses H 20 to yield mainly the distonic radical ion 'CH 2CH 20CH; along with a smaller amount of ionized methyl vinyl ether, namely, CH 2=CHOCH;-. Ring-closed products, such as the oxetane or the propylene oxide ion are not observed. The proportion of •CH 2CH 20CH; increases with decreasing internal energy of the 2-methoxyethanol ion, which indicates a lower critical energy for the pathway leading to this product than for the competitive generation of CH2=CHOCH~•. The present study also uses MI, CAD, and NRMS data to assess the structure of the distonic ion +(CH 3)CHOCH 2. (ring-opened ionized propylene oxide) and evaluate its isomerization proclivity toward the methyl vinyl ether ion.
Journal of Emerging Trends in Engineering and Applied Sciences, 2013
Ion molecule reactions usually occur between reagent ion and neutral sample molecules under chemical ionization (CI) and ion cyclotron (ICR) conditions. The set of Bronsted acids generated in methane CI plasma are all powerful protic acids and are present in the CI source in far greater concentrations than the protonated PEG and PEGDAE ions and the many fragments of these oligomers. However, sample ion/sample molecule (SISM) reactions were observed under CI conditions with large sample size of polar compounds, and are useful in forming MH+ ions for molecular weight determination. These SISM reactions will not be noticed unless studies are made about the variation of CI spectra with sample size. The CH4/CI mass spectra of polyethylene glycol and polyethylene glycol dialkyl ethers contain MH+ ions whose relative abundances are low, variable,and increase with increasing sample size across the chromatographic peaks and not with increasing value of x or n; hence, a major portion of these ions is formed by SISM reactions. The dominant fragment ion in the CH4/CI mass spectra of all PEG and PEGDAE's are the ions at m/z 45 (C2H5O+) and m/z 59 (C3H7O+) respectively. Inthis paper, electronic ionization (EI), CI, and ion molecule reactions of the PEG and PEGMAE's were used to produce C2H5O+ and C3H7O+ ions in the source of an FT/ICR mass spectrometer and were used to react with PEG's and PEGDME's. Reaction profiles of these two sample ions were monitored and their reaction products and profile were also obtained. The ion molecule reaction of C2H5O+ ions from PEG gave spectra similar spectra to those produced by CH4/CI. The reaction profile of isomeric C3H7O+ ions with PEGDAE's follow the same pattern like those observed for the C2H5O+ ions. The relative abundances of the MH+ in the CH4 CI mass spectra of PEG and PEGDAE oligomers increased dramatically with increasing sample size confirming the occurrence of sample ion/sample molecule reactions under normal CI conditions. The limitation of this study include the fact that collision rate constants, the reduced mass (1/μ1/2) of the colliding pair and the proton affinities of PEG and PEGDAE's are not known which might have helped to understand why SISM reactions preferably occurs in the presence of larger concentrations of reagent ions. Further studies needs to be done to access these parameters.