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Positive ion chemistry of elemental fluorine
No full textF2.+ ions have been generated in the external ion source of a FT-ICR mass spectrometer, and their reactivity
with a choice of neutrals, ranging from noble gases to polyatomic molecules, has been investigated. With the exception of He and Ne, all neutrals react with F2.+ at the collision controlled limit, yielding predominantly electron transfer and fragmentation products. Noteworthy, a formal F+ transfer process takes place from the reaction of F2.+ with Ar, among the noble gases, and with CO and N2, among diatomic molecules. The unimolecular and bimolecular reactivity of F2H+, obtained from the F2.+ reaction with H2, allowed the proton affinity of elemental fluorine (PA = 79 +/- 5 kcal mol-1) to be experimentally derived
Gas-phase alkylation and halomethylation of free dialkylhalonium and halomethylium ions
No full textDimethylhalonium ions Me2X+ (X = F, Cl, Br) were prepd. in the gas phase by γ-radiolysis of MeX, and their reactions were studied with substrates contg. either a π- or n-type nucleophilic center, e.g. benzene, toluene, xylene, MeOH. The reactions were studied at MeX pressures 100-760 torr, in the presence of O2 as a thermal radical scavenger, and variable concns. of added NH3. Me2F+ ions react readily with all the substrates studied, giving methylated products whose isomeric compn. depends on the pressure of the gaseous system. Attack by Me2F+ on toluene leads to an intramol. distribution (para/0.5 meta = 2.5) typical of a gas-phase electrophilic displacement reaction, whereas the selectivity towards substrates shows the influence of steric hindrance for the most encumbered substrates. Me2Cl+ and Me2Br+ ions sharply discriminate between n- and π-type basic centers, showing much greater selectivity than Me2F+. The reactivity and selectivity features were also studied for other electrophiles, e.g. +CH2X, formed in minor concns. from the radiolysis of MeX. The mechanisms of the gas-phase methylations are compared with those of different gaseous electrophiles and with those of Friedel-Crafts alkylating agents. The behavior of condensed-phase methylating species and gas-phase Me2F+ ions show significant analogies, traced to their common mode of attack on arom. substrates
Gas-phase reaction of daughter ions from the decay of multitritiated propane with benzene and toluene. Solution of a long-standing anomaly.
No full textThe population of the daughter ions from the decay of multitritiated propane has been sampled by using as a probe their gas-phase reactions with benzene and toluene at pressures up to 400 torr. Tritiated n- and isopropylated arenes account together for 70-75% of the total activity of the decay ions. This observation-and the failure to detect aromatic allylation-removes an early radiochemical anomaly, by showing that decay of tritiated propane yields propyl ions as the most abundant daughter species, following a trend established for all other tritiated hydrocarbons. The abnormally high abundance of allyl ions measured by mass spectrometry is traced to the decomposition C3H7-+ C3H6++ H 2a llowed by its low activation energy, the lack of collisional stabilization, and the long residence time which characterizes operation of a "charge" mass spectrometer. The excitation energy required for the decomposition is likely to arise from the deformation energy of the propyl cations, born from the sudden nuclear transition in a shape reminiscent of the parent hydrocarbon molecule
A Novel route to H2O2+° ions via direct generation of the oxywater cation H2OO+°
No full textThe oxywater cation H2 OO+ was generated in the gas phase by ionization of mixtures containing O3, O2 and H2 O. Different ionic mixtures, rich in either the H2 OO+ or the HOOH+ isomer, were obtained by O3 /O2 /H2 O–O2 /H2 O CI, and by CH3 OH/O2 –CH2 O/O2 CI, respectively. The H2 O2+ ions were characterized by high-resolution CAD mass spectrometry, and structural and energetic effects were examined
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