Mechanism of Multiple-Proton Transfer in Hydrogen-Bonded Clusters in the Gas Phase

2006 ◽  
pp. 1089-1092
Author(s):  
Hiroshi Sekiya ◽  
Kenji Sakota
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Hydrogen Bonded

Stabilities in the gas phase of the hydrogen bonded complexes, YC6H4OH-X−, of substituted phenols, YC6E4OH, with the halide anions X− (Cl−, Br−, I−)

1990 ◽  
Vol 68 (11) ◽  
pp. 2070-2077 ◽  
Author(s):  
Gary J. C. Paul ◽  
Paul Kebarle
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Proton Transfer ◽  
Gas Phase ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Closed Shell ◽  
Bond Energies ◽  
Substituted Phenols ◽  
Hydrogen Bonded

The equilibria, YPhOH + Br− = YPhOH-Br−, involving 26 differently substituted phenols, were determined with a pulsed high pressure mass spectrometer. The −ΔG0 evaluated from the equilibrium constants represent the hydrogen bond free energies in YPhOH-Br−. These data and data for X− = Cl− and I−, determined previously in this laboratory, are used to examine the substituent effects on the hydrogen bonding. It was found that the hydrogen bond energies in YPhOH-X− increase approximately linearly with the gas phase acidities of the phenols, YPhOH. This is in agreement with earlier observations that showed the bond energies in AH-B−, where AH were oxygen and nitrogen acids and B− closed shell anions, increase with increasing acidity of AH.A detailed analysis of the substituent effects, which is possible for YPhOH-X−, shows that the relationship with the acidity of AH can be divided into two parts. One is the increasing extent of actual proton transfer from AH on formation of the hydrogen bonded complex. Such proton transfer occurs in YPhOH-X− only for the series X− = Cl−. The second effect, which occurs for Cl− and is dominant for Br− and I−, is not directly related to the acidity of the phenols (or AH in general) but depends on a similarity of the substituent effects on the acidity and the stabilization of YPhOH-X− (or AH-B− in general). The dominant contribution to YPhOH-X− stabilization in this case is due to the field effects of the substituents, i.e., π delocalization plays only a small part. Therefore, the correlation with the acidity of YPhOH, where π delocalization is important, is not very close. Keywords: hydrogen bonding, substituent effects, ion–molecule equilibria, stability constants, thermochemistry.

Ground-State Long-Range Proton Transfer Controlled by Proton-Accepting Ability of Hydrogen-Bonded Chains: A Theoretical Study

2017 ◽  
Vol 42 (4) ◽  
pp. 384-396
Author(s):  
Hua Fang
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Barrier Height ◽  
Transfer Process ◽  
Ground State ◽  
Point Energy ◽  
Mechanical Methods ◽  
Solvent Molecules ◽  
Proton Transfer Process ◽  
Hydrogen Bonded

The ground-state triple proton transfer (GSTPT) reactions in HCOOH complexing with H2O, CH3OH, C2H5OH and mixed water–alcohol molecules were studied by quantum mechanical methods in the gas phase and in heptane. The triple proton transfer in HCOOH–S1–S2 (S1, S2 = H2O, CH3OH, C2H5OH) systems all occurred in an asynchronous but concerted protolysis mechanism. The formation pattern of the hydrogen-bonded chain was important to reduce the barrier height of the proton transfer process. When the hydrogen-bonded chain consisted of two identical CH3OH or C2H5OH molecules in the HCOOH–S1–S2 complexes, the GSTPT barrier height of HCOOH–S1–S2 decreased by more than 2 kcal mol−1 compared to that of HCOOH–H2O–H2O both in the gas phase and in heptane, because CH3OH and C2H5OH had larger proton-accepting abilities than had H2O. When the two solvent molecules in the hydrogen-bonded chain in the HCOOH–S1–S2 complexes were different, the barrier height of the proton transfer process varied depending on the proton-accepting ability (basicity) of the hydrogen-bonded chain. The bigger the proton-accepting ability (basicity) of the hydrogen-bonded chain, the lower the barrier height of the proton transfer process. Mixed bridging solvent molecules could accumulate their proton-accepting abilities and thus speeded up proton transfer. The solvent effect evidently decreased the zero point energy-corrected barrier heights of HCOOH clusters and increased the asynchronicity of the proton transfer, while the proton transfer mechanisms did not change in heptane.

An experimental study of the reactivity of the hydroxide anion in the gas phase at room temperature, and its perturbation by hydration

1981 ◽  
Vol 59 (11) ◽  
pp. 1615-1621 ◽  
Author(s):  
Scott D. Tanner ◽  
Gervase I. Mackay ◽  
Diethard K. Bohme
Keyword(s):  
Experimental Study ◽  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Room Temperature ◽  
Gas Phase Reactions ◽  
Flowing Afterglow ◽  
Hydroxide Anion

Flowing afterglow measurements are reported which provide rate constants and product identifications at 298 ± 2 K for the gas-phase reactions of OH− with CH3OH, C2H5OH, CH3OCH3, CH2O, CH3CHO, CH3COCH3, CH2CO, HCOOH, HCOOCH3, CH2=C=CH2, CH3—C≡CH, and C6H5CH3. The main channels observed were proton transfer and solvation of the OH−. Hydration with one molecule of H2O was observed either to reduce the rate slightly and lead to products which are the hydrated analogues of the "nude" reaction, or to stop the reaction completely, k ≤ 10−12 cm3 molecule−1 s−1. The reaction of OH−•H2O with CH3—C≡CH showed an uncertain intermediate behaviour.

Sign in / Sign up

Export Citation Format

Share Document