Kinetic and thermodynamic contributions to energy barriers and energy wells: application to proton-bound dimers in gas-phase proton-transfer reactions

1981 ◽  
Vol 103 (25) ◽  
pp. 7465-7469 ◽  
Author(s):  
Douglas E. Magnoli ◽  
Joseph R. Murdoch
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Transfer Reactions ◽  
Energy Barriers ◽  
Proton Transfer Reactions

Gas-phase proton-transfer reactions of the hydronium ion at 298 K

1979 ◽  
Vol 57 (12) ◽  
pp. 1518-1523 ◽  
Author(s):  
Gervase I. Mackay ◽  
Scott D. Tanner ◽  
Alan C. Hopkinson ◽  
Diethard K. Bohme
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Transfer Reactions ◽  
Flowing Afterglow ◽  
Hydronium Ion ◽  
Proton Transfer Reactions

Rate constants measured with the flowing afterglow technique at 298 ± 2 K are reported for the proton-transfer reactions of H3O+ with CH2O, CH3CHO, (CH3)2CO, HCOOH, CH3COOH, HCOOCH3, CH3OH, C2H5OH, (CH3)2O, and CH2CO. Dissociative proton-transfer was observed only with CH3COOH. The rate constants are compared with the predictions of various theories for ion–molecule collisions. The protonation is discussed in terms of the energetics and mechanisms of various modes of dissociation.

The effect of water-mediated catalysis on the intramolecular proton-transfer reactions of the isomers of 5-chlorouracil: a theoretical study

2019 ◽  
Vol 75 (5) ◽  
pp. 554-561
Author(s):  
Jian Zhang ◽  
Xiu Li
Keyword(s):  
Proton Transfer ◽  
Density Functional ◽  
Dft Method ◽  
Intramolecular Proton Transfer ◽  
Transfer Reactions ◽  
Energy Barriers ◽  
Transfer Energy ◽  
Geometrical Structures ◽  
Proton Transfer Reactions ◽  
Mediated Catalysis

The geometrical structures and thermal energies (E), enthalpies (H) and Gibbs free energies (G) of 13 isomers of 5-chlorouracil (5ClU) in the gas and water phases were investigated using the density functional theory (DFT) method at the M06-2X/6-311++g(3df,3pd) level. The isomers of 5ClU can be microhydrated at different molecular target sites. The mono- and dihydrated forms are the most stable in both the gas and water phases, and, because of the intermolecular interactions, the hydrations lead to a degree of change in the stability trend. Two types of isomerizations were considered: the internal H—O bond rotations in which the H atom rotates 180° around the C—O bond and the intramolecular proton-transfer reactions in which an H atom is transferred between an O atom and a neighbouring N atom. The forward and backward energy barriers for isomerizations of nonhydrated 5ClU were calculated. In addition, 16 optimized transition-state structures for water-mediated catalysis on isomerizations of 5ClU were investigated. The forward and backward proton-transfer energy barriers of water-mediated catalysis on isomerizations of 5ClU were obtained. The results indicate that the catalytic effect of two H2O molecules is much greater than that of one H2O molecule in isomerizations of 5ClU.

An experimental study of the reactivity and relative basicity of the methoxide anion in the gas phase at room temperature, and their perturbation by methanol solvation

1982 ◽  
Vol 60 (20) ◽  
pp. 2594-2605 ◽  
Author(s):  
Gervase I. Mackay ◽  
Asit B. Rakshit ◽  
Diethard K. Bohme
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Solvent Free ◽  
Transfer Reactions ◽  
Free Proton ◽  
Proton Transfer Reactions ◽  
Intrinsic Reactivity ◽  
Relative Acidity ◽  
Methoxide Anion

Flowing afterglow measurements at 296 ± 2 K are reported which explore three aspects of the gas-phase acid–base chemistry of the methoxide anion. Firstly, the intrinsic reactivity of this ion has been determined from measurements of rate constants for solvent-free proton-transfer reactions with molecules more acidic than methanol including CH2=C=CH2, C6H5CH3, C2H5OH, C2H2, CH3CN, CH3COCH3, CH3CHO, CH3NO2, and HCN. Secondly, equilibrium constant measurements have been performed for solvent-free proton-transfer reactions which provide a gas-phase scale of acidities for these molecules relative to the acidity of methanol. Finally, rate constants were measured for the reactions of these acids with methoxide ions solvated with up to three molecules of methanol. The results establish trends in reactivity as a function of step–wise solvation when relative acidity is preserved and when a reversal occurs in the relative acidity upon solvation.

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