Stability and reactivity of the benzyl and tropylium cations in the gas phase

1981 ◽  
Vol 59 (11) ◽  
pp. 1592-1601 ◽  
Author(s):  
D. K. Sen Sharma ◽  
P. Kebarle
Keyword(s):  
Excitation Energy ◽  
Temperature Dependence ◽  
Gas Phase ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Fair Agreement ◽  
Internal Excitation ◽  
Hydride Abstraction

A measurement of equilibrium [4]: t-C4H9+ + BzCl = t-C4H9Cl + C7H7+ led to equilibrium constants K4 which are in fair agreement with earlier work by Abboud etal. However, the present temperature dependence predicts a ΔS40 which is sufficiently different from that by Abboud etal. to put in question the indentification of C7H7+ as Bz+ on the basis of the measured ΔS40 value. Therefore experiments were made to confirm that C7H7+ produced in [4] is Bz+ and not the tropylium cation. A C7H7+ cation was produced by hydride abstraction from 1,3,5-cycloheptatriene. The behaviour of that C7H7+ ion was entirely different from C7H7+ produced by chloride abstraction from BzCl or hydride abstraction from toluene. While the benzyl derived C7H7+ engaged in a number of reactions like hydride abstraction, chloride abstraction, addition, condensation, etc., the C7H7+ from the heptatriene remained completely unreactive. On this basis the C7H7+ ions were identified as Bz+ and tropylium+, respectively. Rate constants for several reactions of Bz+ were determined. It is concluded that a rearrangement from benzyl to tropylium cations and vice versa does not occur at least up to 300 °C. The ions also retain their identity if they are produced with considerable internal excitation energy.

Hydration of CN−, NO2−, NO3−, and OH− in the Gas Phase

1971 ◽  
Vol 49 (20) ◽  
pp. 3308-3314 ◽  
Author(s):  
J. D. Payzant ◽  
R. Yamdagni ◽  
P. Kebarle
Keyword(s):  
Temperature Dependence ◽  
Gas Phase ◽  
Bond Dissociation Energy ◽  
Dissociation Energy ◽  
Linear Correlation ◽  
Equilibrium Constants ◽  
Negative Ions ◽  
Thermochemical Data ◽  
Electron Affinities ◽  
Hydration Energies

By measuring the A−(H2O)n−1 + H2O = A−(H2O)n equilibria in the gas phase and their temperature dependence, the equilibrium constants and ΔHn, n–1 and ΔSn, n–1 for some of the hydrates of NO2−, NO3−, CN−, and OH− were determined. Available thermochemical data are used for the evaluation of the total heats of hydration of the above ions. The total heats of hydration were then compared with the ΔH1,0. Relative to the total hydration energies the ΔH1,0 of the above ions were found larger than the ΔH1,0 of the halide ions.An approximate linear correlation was found to exist between ΔH1,0 of negative ions and the heterolytic bond dissociation energy D(A−–H+). With this relationship independent estimates for the electron affinities of NO2 and NO3 could be obtained.The ΔHn, n–1 of OH− were found in essential agreement with earlier measurements from this laboratory and in disagreements with recent measurements (Friedman) which gave much higher values.

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.

Temperature Dependence of Disproportionation–Combination Ratios for Alkyl Radicals in Liquid Methane

1971 ◽  
Vol 49 (17) ◽  
pp. 2861-2867 ◽  
Author(s):  
Hugh A. Gillis
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Gas Phase ◽  
Rate Constants ◽  
Room Temperature ◽  
Transition States ◽  
Alkyl Radicals ◽  
Liquid Methane ◽  
Ethyl Radicals

The ratios of rate constants for disproportionation to combination have been measured for ethyl radicals and for i-propyl radicals in liquid methane between −181 and −94 °C. The radicals were generated by γ-radiolysis of dilute methane solutions of ethylene-d4 or propylene-d6. The activation energy for combination was found to exceed that for disproportionation by 290 ± 30 cal mol−1 for ethyl radicals and by 255 ± 25 cal mol−1 for i-propyl radicals. In both cases the disproportionation—combination ratio in the liquid, extrapolated to room temperature, is greater than that in the gas phase by a factor of about 2.5. These results are interpreted as indicating that disproportionation and combination reactions proceed by way of different transition states.

Kinetics and Temperature Dependence of the Hydration of NO+ in the Gas Phase

1973 ◽  
Vol 51 (3) ◽  
pp. 456-461 ◽  
Author(s):  
Margaret A. French ◽  
L. P. Hills ◽  
P. Kebarle
Keyword(s):  
Temperature Dependence ◽  
Gas Phase ◽  
Rate Constants ◽  
Room Temperature ◽  
Transfer Reaction ◽  
Negative Temperature ◽  
Ion Source ◽  
Third Order ◽  
The Third ◽  
Kinetics Of

The kinetics of the atmospherically important hydration sequence: NO+(H2O)n−1 + H2O = NO+(H2O)n and the transfer reaction NO+(H2O)n + H2O = HNO2 + H+(H2O)n were examined in nitrogen containing small quantities of NO and H2O with a pulsed high pressure ion source mass spectrometer. The room temperature mechanism and rate constants were found to be in agreement with earlier work in other laboratories. The temperature dependence of the reaction was examined for the range 27–157 °C. The transfer reaction does not occur at higher temperatures so that the NO+ hydration equilibria for n = 1 and 2 could be measured leading to ΔH1,0 = 18.5 and ΔH2,1 = 16.1 kcal/mol. The third order forward clustering rate constants were found to have negative temperature coefficients.

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