SN2 reactions in the gas phase. Temperature dependence of the rate constants and energies of the transition states. Comparison with solution

1984 ◽  
Vol 106 (4) ◽  
pp. 959-966 ◽  
Author(s):  
Gary Caldwell ◽  
Tom F. Magnera ◽  
Paul Kebarle
Keyword(s):  
Temperature Dependence ◽  
Gas Phase ◽  
Rate Constants ◽  
Transition States ◽  
Sn2 Reactions ◽  
Phase Temperature

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.

Studies in solvolysis. Part VIII. An entropy correlation related to the reaction of various nucleophiles with malachite green

1977 ◽  
Vol 55 (4) ◽  
pp. 686-692 ◽  
Author(s):  
Stephen Harvey Morris ◽  
John Marshall William Scott ◽  
Frederick Steele
Keyword(s):  
Temperature Dependence ◽  
Malachite Green ◽  
Methyl Iodide ◽  
Rate Constants ◽  
Transition States ◽  
Reaction Coordinate ◽  
Similar Correlation ◽  
Displacement Reactions

The entropies of activation related to the reactions of aqueous malachite green with the nucleophiles water, hydroxide, hydrazine, ammonia, hypochlorite, and sulphite have been calculated from the temperature dependence of the rate constants appropriate to these reactions. The entropies of the transition states for these reactions have been characterized and the transition states shown to be 'reactant like'. A similar correlation, based on data for a series of nucleophiles attacking methyl iodide, suggests that the transition states for the SN2 displacement reactions are also 'reactant like' with respect to the attacking nucleophile. A relationship between two distinct parameters each of which is related to the position of transition states along the reaction coordinate is considered.

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.

Rate constants for formation of bisulfite addition compounds: an examination in terms of No Barrier Theory

2015 ◽  
Vol 93 (2) ◽  
pp. 227-233 ◽  
Author(s):  
J. Peter Guthrie ◽  
Yin-Yin Wu ◽  
Alexander R. Bannister ◽  
Sriyawathie Peiris ◽  
Igor Povar ◽  
...  
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Carbonyl Compounds ◽  
Bond Formation ◽  
Transition States ◽  
Water Soluble ◽  
Definition Of

We report a study of the rates of sulfite addition to carbonyl compounds. This reaction is useful in separating compounds (aldehydes react more extensively than ketones, thus becoming water soluble) because the reaction is readily reversible. Although the reaction is mainly by addition of sulfite dianion, the equilibrium is much more favorable for the addition of bisulfite to give a monoanionic adduct. It is also of interest because bisulfite addition is very favorable; thus, we are dealing with a very strong nucleophile. This work demonstrates that No Barrier Theory can calculate rates for good nucleophiles (cyanide and now sulfite) as well as poor nucleophiles such as water. It has been necessary to develop good ways to handle the anionic tetrahedral adducts (in the case of sulfite as nucleophile, dianionic), which tend to break down in the gas phase unless explicitly solvated, and modified procedures for crowded transition states to allow for some relief of steric congestion while maintaining the essential definition of the distorted species resulting from bond formation without geometry change.

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.

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