A comparison of the relative binding energies of H+ and NO+ to aromatic and haloaromatic bases by high pressure mass spectrometry

1982 ◽  
Vol 60 (7) ◽  
pp. 910-915 ◽  
Author(s):  
John A. Stone ◽  
Dena E. Splinter ◽  
Soon Yau Kong
Keyword(s):  
Mass Spectrometry ◽  
High Pressure ◽  
Proton Affinity ◽  
Marked Effect ◽  
Ion Source ◽  
Binding Energies ◽  
Absolute Value ◽  
Pulsed Electron Beam ◽  
Relative Binding ◽  
Benzene Toluene

Proton transfer equilibria [Formula: see text] and NO+ transfer equilibria [Formula: see text] have been studied for the following bases B, benzene, toluene, o-, m-, and p-xylene. NO+ transfer equilibria for fluoro- and chlorobenzene have also been studied. Pulsed electron beam, high-pressure ion source mass spectrometry has been used to obtain the equilibrium constant K and hence the free energy changes ΔG0 and from van't Hoff plots, ΔH0 and ΔS0. Entropy changes are in general much smaller for NO+ transfer than for H+ transfer but the magnitude of the changes in the proton affinity and NO+ affinity of toluene caused by a fluorine substituent is about the same, even though the absolute value of the proton affinity is greater by a factor of 4. The position of the F substituent on toluene has a marked effect on proton affinity but no effect on NO+ affinity. The latter appears to be responsive only to the inductive effect.

The binding energies of trialkylgermanium cations to water molecules studied by high pressure mass spectrometry

1987 ◽  
Vol 65 (9) ◽  
pp. 2146-2148 ◽  
Author(s):  
John Alfred Stone ◽  
Wilhelmus Johannes Wytenburg
Keyword(s):  
Mass Spectrometry ◽  
High Pressure ◽  
Electron Beam ◽  
Binding Energy ◽  
Thermodynamic Data ◽  
Binding Energies ◽  
Water Molecules ◽  
Pulsed Electron Beam

The binding energies of H2O to R3Ge+ have been measured using pulsed electron beam, high pressure mass spectrometry. van't Hoff plots have yielded thermodynamic data (ΔH0, ΔS0) for the reactions, [5], [Formula: see text]and [7], [Formula: see text]. [Formula: see text] decreases with increasing size of R (CH3 28.6 ± 0.5 kcal mol−1, C4H9 20.6 ± 1.2 kcal mol−1) while [Formula: see text] shows much less change (34.4 ± 0.9 to 30.3 ± 2.8 cal K−1 mol−1). Comparison with data for (CH3)3M+ (M = Si, Sn) shows that binding energy decreases with increasing size of M.

The formation of (CH3)7Si2+ in (CH3)4Si/CH4 mixtures and CH3− exchange reactions between (CH3)4Si, (CH3)4Ge, and (CH3)4Sn studied by high pressure mass spectrometry

1987 ◽  
Vol 65 (12) ◽  
pp. 2849-2854 ◽  
Author(s):  
Anastasia C. M. Wojtyniak ◽  
Xiaoping Li ◽  
John A. Stone
Keyword(s):  
Mass Spectrometry ◽  
High Pressure ◽  
Equilibrium Constant ◽  
Mass Spectrometer ◽  
Excellent Agreement ◽  
Ion Source ◽  
Methyl Groups ◽  
Exchange Reactions ◽  
Equilibrium Reactions ◽  
Association Equilibrium

The association equilibrium [Formula: see text] has been studied in a high pressure mass spectrometer ion source using tetramethylsilane/methane mixtures. Measurement of the equilibrium constant over a range of temperatures yields ΔH0 = −22.3 ± 0.4 kcal mol−1 and ΔS0 = −35.2 ± 0.9 cal mol−1 K−1. Collision-assisted dissociation experiments suggest that the methyl groups retain their integrity in (CH3)7Si2+. Mixed ions such as (CH3)7SiGe+ and (CH3)7GeSn+ were not observed in mixtures of (CH3)4X and (CH3)4Y(X ≠ Y = Si, Ge, Sn). Instead CH3− transfer equilibrium reactions were observed viz. [Formula: see text] (ΔH0 = −10.2 ± 1.2 kcal mol−1, ΔS0 = −3.7 ± 2.4 cal K−1 mol−1) and [Formula: see text], ΔS0 = −0.9 ± 1.6 cal K−1 mol−1. These are in excellent agreement with some published differences in appearance potentials for (CH3)3X+ from (CH3)4X (X = Si, Ge, Sn).

The condensation of trimethylsilylium with water and the proton affinity of trimethylsilanol

1986 ◽  
Vol 64 (3) ◽  
pp. 575-576 ◽  
Author(s):  
John A. Stone ◽  
Anastasia C. M. Wojtyniak ◽  
Willum Wytenburg
Keyword(s):  
Mass Spectrometry ◽  
High Pressure ◽  
Proton Affinity ◽  
Enthalpy Change ◽  
Tert Butanol

The proton affinity (PA) of trimethylsilanol has been determined by high pressure mass spectrometry from the enthalpy change for the reaction [Formula: see text]. ΔH0 = −30.1 ± 1.9 kcal mol−1 giving PA (Me3SiOH) = 183.7 kcal mol−1. This latter value is 10 kcal mol−1 less than that of the carbon analogue, tert-butanol.

Ethyl cation transfer from diethylchloronium to alkyl aromatics studied by high pressure mass spectrometry

1988 ◽  
Vol 66 (5) ◽  
pp. 1239-1248
Author(s):  
Peggy Jane Mathews ◽  
John A. Stone
Keyword(s):  
High Pressure ◽  
Temperature Coefficient ◽  
Rate Constants ◽  
Negative Temperature ◽  
Ion Source ◽  
Positive Temperature ◽  
Reaction Rate Constants ◽  
Benzene Toluene ◽  
Double Well Potential ◽  
Ethyl Cation

Diethylchloronium (C2H5)2Cl+) has been formed in a high pressure (2–4 Torr) ion source using a C2H5Cl/CH4 mixture. (C2H5)2Cl+ reacts with C2H5Cl (Ea = 22 ± 2 kcal mol−1) at temperatures above 500 K to give [Formula: see text]. The reaction of (C2H5)2Cl+ with B (B = benzene, toluene, isopropylbenzene, mesitylene) yields mainly C2H5B+ at temperatures below 500 K but BH+ is also formed at higher temperatures. The further reactions of C2H5B+ include proton transfer to B yielding BH+ (mesitylene), hydride transfer from B (isopropylbenzene), and reaction with C2H5Cl+ (C2H5)2B+ (toluene and benzene) and (C2H5)3B+ (benzene). The rate constants for the reaction (C2H5)2Cl+ + B → C2H5B+ + C2H5B+ + C2H5Cl increase in the order of increasing reaction exothermicity (mesitylene > isopropylbenzene > toluene > benzene). Mesitylene has a negative temperature coefficient, isopropylbenzene has no temperature coefficient, and toluene and benzene show positive temperature coefficients of reaction rate constants consistent with the double well potential theory for gas phase SN2 reactions.

scholarly journals Pyrolysis of C2H7+ and other Ion–Molecule Reactions in Methane containing Traces of Ethane

1975 ◽  
Vol 53 (15) ◽  
pp. 2268-2274 ◽  
Author(s):  
Margaret French ◽  
Paul Kebarle
Keyword(s):  
Temperature Dependence ◽  
Proton Affinity ◽  
Preexponential Factor ◽  
Thermal Reaction ◽  
Ion Source ◽  
Positive Temperature ◽  
Source Pressure ◽  
Pulsed Electron Beam ◽  
Ion Molecule Reactions ◽  
Higher Temperature

The major reactions in methane containing traces of ethane were studied with a pulsed electron beam high ion source pressure mass spectrometer. The CH4: C2H6 ratios were changed from 50:1 to 100 000:1 at reaction temperatures between 28–210 °C. The reaction 1: CH5+ + C2H6 = CH4 + C2H7+ still proceeded from left to right even at the highest dilution ratios. Measurement of the C2H7+/CH5+ ratio under these conditions leads to a lower limit of the proton affinity difference PA(C2H6)–PA(CH4) > 10 kcal/mol. This result is in agreement with measurements by Bohme.It was observed that C2H7+ decomposes slowly at 30 °C. The decomposition becomes more rapid at higher temperature. Measurements of the temperature dependence of the thermal reaction 2: C2H7+ + CH4 = C2H5+ + H2 + CH4, and an Arrhenius plot of k2 led to the activation energy E2 = 10.5 kcal/mol and preexponential factor A2 = 8.3 × 10−8 (cm3 molecule−1 s−1). Assuming E2 = ΔH2 one obtains ΔHf(C2H7+) = 208.5 ± 2 kcal/mol and PA(C2H7+) = 137.4 ± 2 kcal/mol. This is close to the proton affinity PA(C2H7+) = 139 ± 2 kcal/mol that can be deduced from Bohme's results.At higher dilution ratios the ion C2H5+ was observed to react not only with ethane but also with methane by reaction 6: C2H5+ + CH4 = C3H7+ + H2, k6 ≈ 1 × 10−14 cm3 molecule−1 s−1 at 86 °C. The reaction has positive temperature dependence.

Proton-induced reactions of [2.2]-paracyclophane in the gas phase. A study by FT-ICR-spectrometry and DFT calculation

2017 ◽  
Vol 23 (6) ◽  
pp. 327-340
Author(s):  
Heinz-Hermann Büker ◽  
Hans-Friedrich Grützmacher
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Vinyl Ether ◽  
Proton Affinity ◽  
Ion Source ◽  
Ethyl Vinyl Ether ◽  
Dft Methods ◽  
Ethyl Vinyl ◽  
Carbenium Ions ◽  
Ft Icr

The reactions of the [2-2]-paracyclophane 1 and the [2-2]-metaparacyclopane 2 in the gas phase after protonation by CI(CH4) or CI(I-C4H10) were studied by FT-ICR mass spectrometry. The ions C16H17+ produced in the external ion source of the FT-ICR instrument were transferred into the ICR cell containing the neutral reactant, and the reactions were analyzed measuring the efficiency of the transfer of a proton to a series of bases with known proton affinity and gas phase basicity as well as the efficiency of the ion-molecule reaction with ethyl vinyl ether. Both reaction types show that the ions C16H17+ produced by chemical ionization (CI) consist of two sets of isomeric ions A and B which exhibit distinctly different behavior on deprotonation and of the reaction with ethyl methyl ether. Isomer(s) A (about 65% of the ion population) react efficiently with this vinyl ether by an addition/elimination process typical of primary and secondary benzylic carbenium ions, while isomer B (about 35% of the ion population) undergoes only an ineffective deprotonation by the vinyl ether. By bracketing deprotonation, it is shown that A is actually composed of two isomers A1 and A2 with slightly different proton affinity and gas phase basicity. These two ions have been identified using CA-mass spectrometry as protonated 3-phenethylstyrene (A1) and protonated 4-phenethylstyrene (A2). The CA-mass spectrum of the isomer B indicated that these ions C16H17+ correspond to protonated 1-(ethyl phenyl)-1-phenyl-ethene. This agrees with the rather strong basicity of the conjugated base of ions B, which results in a slow deprotonation. A protonated 1-(ethyl phenyl)-1-phenyl-ethene can arise from a protonated 2-phenethylstyrene by H- and subsequent phenyl shifts, but requires the preceding rearrangement of the protonated [2.2]-paracyclophane into the protonated isomer “[2.2]-orthocyclophane” – the 1,5-dibenzocyclooctadiene. The possibility of such a deep-sited rearrangement was studied by the computation of the relevant reaction routes applying DFT-methods at the level B3LYP/6-311+g(3d,2p)//B3LYP/3-21g) to analyze the reaction mechanisms.

Sign in / Sign up

Export Citation Format

Share Document