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.

Ion molecule reactions in ethane. Thermochemistry and structures of the intermediate complexes: C4H11+ and C4H10+ formed in the reactions of C2H5+ and C2H4+ with C2H6

1980 ◽  
Vol 58 (21) ◽  
pp. 2262-2270 ◽  
Author(s):  
K. Hiraoka ◽  
P. Kebarle
Keyword(s):  
Low Temperature ◽  
Rate Constant ◽  
Reaction System ◽  
Major Product ◽  
Ion Source ◽  
Source Pressure ◽  
Pulsed Electron Beam ◽  
Ion Molecule Reactions ◽  
High Temperature Reaction ◽  
Induced Dipole

The reactions of C2H5+ and C2H4+ with ethane were studied in a pulsed electron beam high ion source pressure mass spectrometer. Ethane at variable pressures in the 10–100 m Torr range in ~5 Torr hydrogen was used in experiments covering the temperature range −145 to 400 °C. Reaction [7]: C2H5+ + C2H6 = sec-C4H9+ + H2 was found to have a rate constant whose magnitude decreased with temperature: k7 = 10−5.12 T−2 (molecule−1 cm3 s−1). The reaction proceeds via a C4H11+ (b) intermediate, which at low temperature can be stabilized and becomes the major product. The rate constant for thermal decomposition of C4H11(b) by reaction [6t]: C4H11+ (b) = sec-C4H9+ + H2 could be measured. The activation energy was found to be E6t = 9.6 kcal/mol. From consideration of the above data and the known ΔH7, it was concluded that C4H11+ (b) has the structure[Formula: see text]Before dissociation to sec-C4H9+ + H2, this ion rearranges to[Formula: see text]The barrier for this rearrangement is ~9.6 kcal/mol.C2H4+ reacts with C2H6 to give C4H10+ (d) at low temperatures. At high temperatures C4H10+ (d) becomes an intermediate in the dissociation to sec-C3H7+ + H2. The formation of C4H10+ at low temperature has a rate constant whose magnitude decreases with temperature. The temperature dependence of the equilibrium constant K10 for the reaction [10]: C2H4+ + C2H6 = C4H10+ (d) could be determined. This led to ΔH10 = −15.3 kcal/mol. The rate constant for the high temperature reaction [11]: C2H4+ + C2H6 = sec-C3H7+ + H2 was k11 = 8.4 × 10−10 exp (−3.9/RT kcal/mol) (molecule−1 cm3 s−1). A potential energy diagram for the reaction system is proposed. C4H10+ (d) is probably a complex between C2H4+ and C2H6 held largely by ion induced dipole process. Reaction [11] probably proceeds via C4H10+ (d) → n-C4H10+ → sec-C3H7+ + H2. The barrier between C7H10+ (d) and n-C4H10+ is ~20 kcal/mol.

Formation of tert-butyl cation in methane

1976 ◽  
Vol 54 (11) ◽  
pp. 1739-1743 ◽  
Author(s):  
K. Hiraoka ◽  
P. Kebarle
Keyword(s):  
Temperature Dependence ◽  
Gas Phase ◽  
Arrhenius Plot ◽  
Ion Source ◽  
Probable Mechanism ◽  
Positive Temperature ◽  
Phase Reaction ◽  
Source Pressure ◽  
Gas Phase Reaction ◽  
Pure Methane

The reactions of CH3+ with pure methane in the torr range show an interesting temperature dependence. C2H5+ is formed at all temperatures by the well known reaction: CH3+ + CH4 = C2H5+ + H2. In the lowest temperature interval studied (105–125 K) C2H5+ adds two CH4 molecules to give a C4H13+ species. At higher temperatures only one CH4 molecule is added on. The resulting C3H9+ then reacts with one more CH4 molecule according to reaction 6.[Formula: see text]The rate constant k6 is found to be second order and has a positive temperature dependence. An Arrhenius plot gives:[Formula: see text]At temperatures above 200 K reaction 6 ceases to occur since C3H9+, being unstable at high temperatures, decomposes to s-C3H7+ + H2.The reactions were studied using ultra pure methane irradiated with electrons in a pulsed beam high ion source pressure mass spectrometer.The gas phase reaction mechanism for the formation of t-C4H9+ is found to bear close re-semblance to the probable mechanism by which the t-C4H9+ ion is formed from methane dissolved in superacid media.

Gas phase ion equilibria studies of the proton in hydrogen sulfide and hydrogen sulfide – water mixtures. Stabilities of the hydrogen bonded complexes: H+(H2S)x(H2O)y

1977 ◽  
Vol 55 (1) ◽  
pp. 24-28 ◽  
Author(s):  
Kenzo Hiraoka ◽  
Paul Kebarle
Keyword(s):  
Hydrogen Sulfide ◽  
Temperature Dependence ◽  
Gas Phase ◽  
Ion Source ◽  
Cluster Ions ◽  
Exchange Reactions ◽  
Pulsed Electron Beam ◽  
Mixed Cluster ◽  
Association Reaction ◽  
Gas Phase Ion

The temperature dependence of the equilibria [Formula: see text] was measured for n = 1 to 5 in a pulsed electron beam mass spectrometer with a high pressure ion source. The ΔHn+1,n values obtained were (2,1) 15.4, (3,2) 9.1, (4,3) 8.4, (5,4) 6.7 kcal/mol. Possible structures of the clustered ions are proposed.Addition of water vapor leads to mixed cluster ions such as H+(H2S)x(H2O)y, with x + y from 1 to 6, observed as the ion source temperature was decreased to −100 °C. The temperature dependence of the equilibria for the exchange reactions [Formula: see text]and the association reaction [Formula: see text]were also measured. For all ions measured, the hydration process is energetically more favorable than the solvation by H2S.

The gas phase ion chemistry and proton affinity of hexamethyldisiloxane studied by high pressure mass spectrometry

1987 ◽  
Vol 65 (10) ◽  
pp. 2454-2460 ◽  
Author(s):  
Xiaoping Li ◽  
John Alfred Stone
Keyword(s):  
Proton Transfer ◽  
Proton Affinity ◽  
Rate Constants ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Ion Source ◽  
Positive Temperature ◽  
Ion Chemistry ◽  
Gas Phase Ion Chemistry ◽  
Proton Transfer Reactions

The ion chemistry of hexamethyldisiloxane ((CH3)3SiOSi(CH3)3, HMDS) has been studied under chemical ionization conditions at ion source temperatures of 300–600 K and pressures of 2–4 Torr. Highly exothermic proton transfer to HMDS from CH5+ and C2H5+ leads mainly to loss of CH3 but with decreasing exothermicity the yield of HMDSH+ increases such that transfer from t-C4H9+ (ΔH0 = −7.5 kcal mol−1) yields almost exclusively HMDSH+. Although HMDSH+ transfers (CH3)3Si+ rather than a proton to most reference bases, the proton affinity of HMDS has been determined from van't Hoff plots using the equilibrium method with methylaromatics as reference bases. PA(HMDS) = 203.4 kcal mol−1 is in excellent accord with an earlier estimate of 203 kcal mol−1 obtained by the bracketing method. The rate constants for these proton transfer reactions show very large negative temperature coefficients in the exothermic directions which are consistent with the reactions of charge delocalized ions and/or reactions in which considerable loss of rotational freedom occurs along the reaction coordinate. The rate constants in the reverse directions have a positive temperature coefficient only when the endothermicity is significant (>2.5 kcal mol−1).

Alkylation of benzene by alkyl cations. Stability of the tert-butyl benzenium ion

1982 ◽  
Vol 60 (18) ◽  
pp. 2325-2331 ◽  
Author(s):  
D. K. Sen Sharma ◽  
S. Ikuta ◽  
P. Kebarle
Keyword(s):  
Gas Phase ◽  
Equilibrium Constants ◽  
Ion Source ◽  
Phase Reaction ◽  
Source Pressure ◽  
Pulsed Electron Beam ◽  
Gas Phase Reaction ◽  
Alkyl Cations ◽  
Alkylation Of Benzene ◽  
Energy Formula

The kinetics and equilibria of the gas phase reaction [1] tert-C4H9+ + C6H6 = tert-C4H9C6H6+ were studied with a high ion source pressure pulsed electron beam mass spectrometer. Equilibria [1] could be observed in the temperature range 285–325 K. van't Hoff plots of the equilibrium constants led to [Formula: see text] and [Formula: see text]. The rate constants at 305 K were klf = 1.5 × 10−28 molecules−2 cm6 s−1 and klr = 2.9 × 10−1 molecules−1 cm3 s−1. tert-C4H9C6H6+ dissociates easily via [lr] not only because of the low dissociation energy [Formula: see text] but also because of the unusually favorable entropy [Formula: see text]. The occurrence of transalkylation reactions: tert-C4H9C6H6+ + alkylbenzene = tert-C4H9 alkylbenzene+ + benzene, was discovered in the present work.

Hydrogen bonding solvent effect on the basicity of primary amines CH3NH2, C2H5NH2, and CF3CH2NH2

1981 ◽  
Vol 59 (1) ◽  
pp. 151-155 ◽  
Author(s):  
Yan K. Lau ◽  
P. Kebarle
Keyword(s):  
Free Energy ◽  
Energy Difference ◽  
Ion Source ◽  
Primary Amines ◽  
Hydration Free Energy ◽  
Ion Hydration ◽  
Free Energy Difference ◽  
Source Pressure ◽  
Pulsed Electron Beam ◽  
Good Agreement

The equilibria RNH3+(H2O)n−1 + H2O = RNH3+(H2O)n were measured for R = CH3, C2H5, and CF3CH2 from n = 1 to n = 3 with a pulsed electron beam high ion source pressure mass spectrometer. The proton and hydrate transfer equilibria CH3NH3+(H2O)n + C2H5NH2 = CH3NH2 + C2H5NH3+(H2O)n were measured for n = 0 to n = 3. These data allow the evaluation of ΔH0 and ΔG0 for the reactions: R0NH3+(H2O)n + RNH3+ = R0NH3+ + RNH3+(H2O)n. ΔH0 = δΔH00,n(RNH3+), ΔG = δΔG00,n(RNH3+). These data are compared with δΔE0,3 (STO-3G) evaluated by Hehre and Taft. In general good agreement is observed at n = 3. The δΔH00,3(RNH3+) ≈ δΔE0,3(RNH3+) are also found close to the ion hydration free energy difference in aqueous solutions.

Gas phase ion equilibria: heats of formation of acylium ions RCO+ and protonated acids RC(OH)2+; gas phase catalysis of proton shift RC(OH)2+ → RCO(OH2)+

1979 ◽  
Vol 57 (24) ◽  
pp. 3205-3215 ◽  
Author(s):  
W. R. Davidson ◽  
S. Meza-Höjer ◽  
P. Kebarle
Keyword(s):  
Gas Phase ◽  
Negative Temperature ◽  
Ion Source ◽  
Activation Energy Barrier ◽  
Third Order ◽  
Source Pressure ◽  
Pulsed Electron Beam ◽  
Proton Shift ◽  
Gas Phase Ion ◽  
Good Agreement

The equilibria [2]: [Formula: see text] for R = CH3, C2H5, and C6H5 were studied in a pulsed electron beam high ion source pressure mass spectrometer. van't Hoff plots led to ΔH2 values: (CH3), 24.6; (C2H5), 22.7; (C6H5), 21.9 kcal/mol. ΔHf(RC(OH)2+) were obtained from gas phase basicity ladders combined with the new ΔHf(t-butyl+) = 163 kcal/mol (Beauchamp). The ΔHf(RC(OH)2+) were: (CH3), 71.3; (C2H5), 63.6; (C6H5), 95.5 kcal/mol. Combination of ΔH2 with ΔHf(RC(OH)2+) leads to ΔHf(RCO+): (CH3), 153.7; (C2H5), 144; (C6H5), 174.6 kcal/mol. These results are in agreement with selected data from appearance potentials. The energies and structures of the participants in reaction [2] were calculated by MINDO/3 and STO-3G. MINDO/3 gave good agreement with ΔH2. The establishment of the equilibria [2] was unusually slow. A study of the kinetics revealed that k2f is approximately third order, unusually small, and has an unusually large negative temperature coefficient. Furthermore, reaction [2] was found to be catalyzed by RCOOH. An explanation of these observations is given by assuming that the proton shift RCO(OH2)+ → RC(OH)2+ has a large activation energy barrier in the gas phase. This barrier is removed by formation of a hydrogen bonded complex with RCOOH.

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.

Stabilities of complexes (N2)nH+, and (O2)nH+ for n = 1 to 7 based on gas phase ion-equilibria measurements

1979 ◽  
Vol 57 (16) ◽  
pp. 2159-2166 ◽  
Author(s):  
K. Hiraoka ◽  
P. P. S. Saluja ◽  
P. Kebarle
Keyword(s):  
Electron Beam ◽  
Gas Phase ◽  
Equilibrium Constants ◽  
Ion Source ◽  
Large Decrease ◽  
Proton Affinities ◽  
Source Pressure ◽  
Pulsed Electron Beam ◽  
The Stability ◽  
Gas Phase Ion

The equilibria Bn−1H+ + B = BnH+ for B = N2, CO, and O2 were measured with a pulsed electron beam high ion source pressure mass spectrometer. Equilibria up to n = 7 could be observed. van't Hoff plots of the equilibrium constants lead to ΔGn−1,n0, ΔHn−1,n0, and ΔSn−1,n0. While the proton affinities increase in the order O2 < N2 < CO, the stabilities of the B2H+ towards dissociation to BH+ + B increase in the reverse order, i.e. CO < N2 < O2. The stabilities towards dissociation of B for BnH+ where n > 2 are much lower for all three compounds; however for N2 and CO the stability decreases only very slowly from n = 3 to n = 6, then there is a large fall off for n = 7. The (O2)nH+ clusters show large decrease of stabilities as n increases. The BnH+ (for n > 3) of CO are more stable than those of N2 or O2. The above experimental results can be partially explained with the help of results from molecular orbital STO-3G calculations for B, BH+, and B2H+ and general considerations. BH+ and B2H+ for CO and N2 are found to be linear while those for O2 are bent. The most stable O2H+ is a triplet, while (O2)2H+ is a quintuplet.

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