Chemical ionization of phenyl n-propyl ether and methyl substituted analogs: Propene loss initiated by competing proton transfer to the oxygen atom and the aromatic ring.

The mechanism of propene loss from protonated phenyl n-propyl ether and a series of mono-, di-, and trimethylphenyl n-propyl ethers has been examined by chemical ionization (CI) mass spectrometry in combination with tandem mass spectrometry experiments. The role of initial proton transfer to the oxygen atom and the aromatic ring, respectively, has been probed with the use of deuterated CI reagents, D2O, CD3OD, and CD3CN (given in order of increasing proton affinity), in combination with deuterium labeling of the ß position of the n-propyl group or the phenyl ring. The metastable [M + D](+) ions of phenyl n-propyl ether-formed with D2O as the CI reagent-eliminate C3H5D and C3H6 in a ratio of 10:90, which indicates that the added deuteron is incorporated to a minor extent in the expelled neutral species. In the experiments with CD3OD as the CI reagent, the ratio between the losses of C3H5D and C3H6 from the metastable [M + D](+) ions of phenyl n-propyl ether is 18:82, whereas the ratio becomes 27:73 with CD3CN as the reagent. A similar trend in the tendency to expel a propene molecule that contains the added deuteron is observed for the metastable [M + D](+) ions of phenyl n-propyl ether labeled at the ß position of the alkyl group. Incorporation of a hydrogen atom that originates from the aromatic ring in the expelled propene molecule is of negligible importance as revealed by the minor loss of C3H5D from the metastable [M + H](+) ions of C6D5OCH2CH2CH3 irrespective of whether H2O, CH3OH, or CH3CN is the CI reagent. The combined results for the [M + D](+) ions of phenyl n-propyl ether and deuterium-labeled analogs are suggested to be in line with a model that assumes that propene loss occurs not only from species formed by deuteron transfer to the oxygen atom, but also from ions generated by deuteron transfer to the ring. This is substantiated by the results for the methyl-substituted ethers, which reveal that the position as well as the number of methyl groups bonded to the ring exert a marked effect on the relative importances of the losses of C3H5D and C3H6 from the metastable [M + D](+) ions of the unlabeled methyl-substituted species.

Formation and characterization of the sulfur-containing distonic radical anion, [Formula: see text], in the gas phase, in the gas phase.

The reactions of the atomic oxygen radical anion O(-) with CH3-S-CH2-CN m the gas phase have been examined with Fourier transform ion cyclotron resonance in combination with tandem mass spectrometric experiments performed with a double-focusing quadrupole hybrid instrument. Deuterium labeling has revealed that the O(-) ion reacts with CH3-S-CH2-CN by proton abstraction from the methylene group as well as by competing 1,1- and 1,3-H 2 (+) abstractions to afford isomeric radical anions. High kinetic energy (8 keV) collision-induced charge reversal experiments indicate that the 1,1-H 2 (+.) -abstraction leads to a [Formula: see text] carbene ion, whereas the 1,3-H 2 (+) abstraction yields a novel sulfur-containing distonic radical anion, which is formulated as [Formula: see text].

Insertion reactions of metal carbonyl anions with methyl formate in the gas phase as revealed by (13)C- and D-labeling.

School of Chemistry, University of New South Wales, Kensington, Australia Institute of Mass Spectrometry, University of Amsterdam, Nieuwe Achtergracht The gas-phase reactions of coordinatively unsaturated metal carbonyl anions (M(CO) n (-) , M=Cr, Mn, Fe, Co; n=0-3 and Co(CO)nNO(-), n=0-2) with unlabeled and D- and (13)C-labeled methyl formate have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The reactions proceed in most instances by loss of one or more CO molecules from the collision complex. In the reactions of the dicarbonyl and tricarbonyl anions with H(13)COOCH3, part of the eliminated carbon monoxide molecules contain the label revealing the occurrence of initial insertion of the metal center into the bonds adjacent to the carbonyl function of the substrate with formation of five- or six-coordinate intermediates, respectively. In addition, the MnCCO) 3 (-) , Fe(CO) 2 (-) , and CoCCO) 2 (-) ions react by the loss of methanol and a [C,H2,O] neutral species. The D- and (13)C-labeling show that methanol is expelled in a reductive elimination from a five- or six-coordinate species, whereas the [C,H2,O] loss is a more complex process possibly involving the competing losses of formaldehyde and CO + H2. In the reaction of Fe(CO) 3 (-) with H 13 (13) COOCH3, a facile consecutive exchange of all three CO ligands of the reactant ion for (13)CO is observed. This novel reaction appears to involve initial insertion into the H(13)CO-OCH3-bond followed by facile hydrogen shifts from the formyl ligand to a CO Hgand prior to the loss of unlabeled methyl formate.

Gas-phase reactions between O(-.) and C 6H 5F: On the acidity of fluorobenzene and 1,4-difluorobenzene.

The gas-phase reactions of negative ions (O(-.), NH 2 (-) , C2H5NH(-), (CH3)2N(-), C6H 5 (t-) , and CH3SCH 2 (-) ) with fluorobenzene and 1,4-difluorobenzene have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The O(-.) ion reacts predominantly by (1) proton abstraction, (2) formal H 2 (+.) abstraction, and (3) attack on an unsubstituted carbon atom. In addition to these processes, attack on a fluorine bearing carbon atom yielding F(-) and C6H4FO(-) ions occurs with 1,4-difluorobenzene. Site-specific deuterium labeling reveals the occurrence of competing 1,2-, 1,3-, and 1,4-H 2 (+.) abstractions in the reaction of O(-.) with fluorobenzene. Attack of the O(-.) ion on the 3- and 4-positions in fluorobenzene with formation of the 3- and 4-fluorophenoxide ions, respectively, is preferred to reaction at the 2-position, as indicated by the relative extent of loss of a hydrogen and a deuterium atom in the reactions with labeled fluorobenzenes. The NH 2 (-) , C2H5NH(-), (CH3)2N(-), C6H 5 (-) , and CH3SCH 2 (-) anions react with fluoroberuene and 1,4-difluorobenzene only by proton abstraction. The relative importance of H(+) and D(+) abstraction in the reaction of these anions with labeled fluorobenzenes indicates that the 2-position in fluorobenzene is more acidic than the 3- and 4-positions, suggesting that the literature value of the gas-phase acidity of this compound (ΔH acid (o) = 1620 ± 8 kJ mol(-1)) refers to the former site. Based on the occurrence of reversible proton transfer between the CH3O(-) ion and 1,4-difluorobenzene, the ΔH acid (o) of this compound is redetermined to be 1592 ± 8 kJ mol(-1).

Gas-phase ion-molecule reactions of the CH3O (+) cation.

The methoxy cation, CH30(+), formed by collision-induced charge reversal of methoxr anions with a kinetic energy of 8 keY, has been differentiated from the isomenric CH2OH(+) ion by performing low kinetic energy ion-molecule reactions In the radiofrequency-only quadrupole of a reverse-geometry double-focusing quadrupole hybrid mass spectrometer. The methoxy cation reacts with CH3SH, CH3-CH=CH2, (CH3)2O, and CH3CH2Cl by electron transfer, whereas the CH2OH(+) ion reacts by proton transfer with these substrates.