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.

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.

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.

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.

Solvation of Cl− and O2− with H2O, CH3OH, and CH3CN in the gas phase

1973 ◽  
Vol 51 (15) ◽  
pp. 2507-2511 ◽  
Author(s):  
R. Yamdagni ◽  
J. D. Payzant ◽  
P. Kebarle
Keyword(s):  
High Pressure ◽  
Temperature Dependence ◽  
Gas Phase ◽  
Experimental Technique ◽  
Equilibrium Constants ◽  
Ion Source ◽  
Mass Spectrometric ◽  
Mass Spectrometric Detection ◽  
Free Energies

Determination of the temperature dependence of the equilibrium constants Kn,n−1 for the reactions A −Bn = A −Bn−1 + B where A− equals Cl− and O2− and B is HOH, CH3OH, or CH3CN leads to the corresponding ΔH0n−1, ΔG0n−1,n, and ΔS0n−1,n values. The experimental technique is based on mass spectrometric detection of ions escaping from a high pressure ion source. At n = 1, Cl− is solvated most strongly by methanol, then CH3CN and HOH. At higher n a cross over is observed with water becoming the best solvent. These results are in agreement with the positive transfer enthalpies and free energies for Cl− from the liquid solvents HOH → CH3OH and HOH → CH3CN reported in the literature.O2− is solvated more strongly than Cl− appearing thus as an ion of "size" intermediate between Cl− and F− Again CH3OH gives the highest interaction for n = 1, however for n > 1 water gives stronger interactions.

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.

Relative methylmercury cation affinities in the gas phase determined by high pressure mass spectrometry

1981 ◽  
Vol 59 (12) ◽  
pp. 1779-1786 ◽  
Author(s):  
John A. Stone ◽  
Dena E. Splinter
Keyword(s):  
High Pressure ◽  
Gas Phase ◽  
External Rotation ◽  
Equilibrium Constants ◽  
Partition Functions ◽  
Pulsed Electron Beam ◽  
Nitrogen Bases ◽  
Relative Affinity ◽  
The Difference ◽  
Soft Acid

A pulsed electron beam, high pressure mass spectrometer has been used to determine equilibrium constants for the exchange of CH3Hg+ between bases; [Formula: see text] A series of aromatic, hydrocarbon bases has been studied at 417 K and several nitrogen bases have been studied at 580 K. There is a good linear correlation between differences in CH3Hg+ affinity (ΔG0) and H+ affinity for bases in each series. The single sulfur base examined ((C3H7)2S) shows anomalously high relative affinity for CH3Hg+ compared with H+ while two oxygen bases (CH3COOCH3 and C6H5NO2) show lesser relative affinity. These results are in qualitative agreement with the hard–soft acid base theory. ΔH0 and ΔS0 values have been obtained from Arrhenius plots. For a pair of aromatic bases (toluene–ethylbenzene) ΔH0 is of the same magnitude as that for H+ and ΔS0 may be calculated using partition functions for translation and external rotation. For toluene/methylacetate the difference in binding energy is much greater for H+ than for CH3Hg+ and a similar calculation of ΔS0 gives a result not consistent with the experimental value.

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