Dynamics of Endoergic Bimolecular Proton Transfer Reactions:  F-+ ROH → HF + RO-(R = H, CH3, CH3CH2, (CH3)2CH, and (CH3)3C)

DeTuri, Vincent F.; Su, and Moon A.; Ervin, Kent M.

doi:10.1021/jp9842392

Cited by 24 publications

(27 citation statements)

References 83 publications

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“…The observed OO frequency in ice I is 220 cm −1 3. This frequency increases to 1063 cm −1 in the HO − ⋅⋅⋅HOH complex, which compares very well with the value of 1082 cm −1 reported in the literature 59. A poorer agreement is found between the LS and ab initio ω NN frequencies of the (NH 3 ) 2 dimer (212 and 103 cm −1 , respectively)60 and for the (HF) dimer (197 and 160 cm −1 , respectively).…”

Section: Resultssupporting

confidence: 89%

Absolute Rate Calculations: Atom and Proton Transfers in Hydrogen‐Bonded Systems

2005

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We calculate energy barriers of atom‐ and proton‐transfer reactions in hydrogen‐bonded complexes in the gas phase. Our calculations do not involve adjustable parameters and are based on bond‐dissociation energies, ionization potentials, electron affinities, bond lengths, and vibration frequencies of the reactive bonds. The calculated barriers are in agreement with experimental data and high‐level ab initio calculations. We relate the height of the barrier with the molecular properties of the reactants and complexes. The structure of complexes with strong hydrogen bonds approaches that of the transition state, and substantially reduces the barrier height. We calculate the hydrogen‐abstraction rates in H‐bonded systems using the transition‐state theory with the semiclassical correction for tunneling, and show that they are in excellent agreement with the experimental data. H‐bonding leads to an increase in tunneling corrections at room temperature.

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Section: Resultssupporting

confidence: 89%

Absolute Rate Calculations: Atom and Proton Transfers in Hydrogen‐Bonded Systems

2005

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“…Rotational constants and vibrational frequencies for the complexes and products were computed at the HF/6-31G(d) level using Gaussian 94, and vibrational frequencies are scaled by 0.8953 . Table lists the calculated frequencies for the complexes; product molecule frequencies have been reported previously . Low-frequency torsional motions can be treated as harmonic oscillators, free rotors, or hindered rotors.…”

Section: Methodsmentioning

confidence: 99%

“… The threshold energy difference between the two reaction channels in reaction 3 is related to the gas-phase acidity of the alcohol by eq 4 The approximation on the right-hand side of eq 4a assumes that there are no reverse activation barriers for the two dissociation channels, which is reasonable for most proton-bound complexes . To extract the two threshold energies, the energy-dependent branching ratio between the two channels is modeled explicitly using the RRKM theory model developed recently by Rodgers and Armentrout .…”

Section: Introductionmentioning

confidence: 99%

Competitive Threshold Collision-Induced Dissociation: Gas-Phase Acidities and Bond Dissociation Energies for a Series of Alcohols

1999

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Energy-resolved competitive collision-induced dissociation methods are used to measure the gas-phase acidities of a series of alcohols (methanol, ethanol, 2-propanol, and 2-methyl-2-propanol). The competitive dissociation reactions of fluoride−alcohol, [F-·HOR], alkoxide−water, [RO-·HOH], and alkoxide−methanol [RO-·HOCH3] proton-bound complexes are studied using a guided ion beam tandem mass spectrometer. The reaction cross sections and product branching fractions to the two proton transfer channels are measured as a function of collision energy. The enthalpy difference between the two product channels is found by modeling the reaction cross sections near threshold using RRKM theory to account for the energy-dependent product branching ratio and kinetic shift. From the enthalpy difference, the alcohol gas-phase acidities are determined relative to the well-known values of HF and H2O. The measured gas-phase acidities are Δacid H 298(CH3OH) = 1599 ± 3 kJ/mol, Δacid H 298(CH3CH2OH) = 1586 ± 5 kJ/mol, Δacid H 298((CH3)2CHOH) = 1576 ± 4 kJ/mol, and Δacid H 298((CH3)3COH) = 1573 ± 3 kJ/mol.

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“…Viggiano and Morris have concluded that rotational and translational energy are equally available for driving slightly endothermic charge transfer processes [58]. In other cases, the precision afforded by analysis of competitive CID processes (see below) has permitted evaluations which suggest that rotational energy is not active in promoting proton transfer reactions [59,60]. At present, there are no guiding principles that elucidate which systems should or should not include rotational energy.…”

Section: Internal Energy Of the Reactants: Rotationalmentioning

confidence: 99%

Mass spectrometry—Not just a structural tool: The use of guided ion beam tandem mass spectrometry to determine thermochemistry

Armentrout

2002

J. Am. Soc. Mass Spectrom.

175

180

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Guided ion beam tandem mass spectrometry has proved to be a robust tool for the measurement of thermodynamic information. Over the past twenty years, we have elucidated a number of factors necessary to make such thermochemistry accurate. Careful attention must be paid to the reduction of the raw data, ion intensities versus laboratory ion energies, to a more useful form, reaction cross sections versus relative kinetic energy. Analysis of the kinetic energy dependence of cross sections for endothermic reactions can then reveal thermodynamic data for both bimolecular and collision-induced dissociation (CID) processes. Such analyses need to include consideration of the explicit kinetic and internal energy distributions of the reactants, the effects of multiple collisions, the identity of the collision partner in CID processes, the kinetics of the reaction being studied, and competition between parallel reactions. This work provides examples illustrating the need to consider this multitude of effects along with details of the procedures developed in our group for handling each of them. ( W hen does a mass spectrometer become an ion beam instrument? Is this defined by the instrument, by whether the operator is an analytical or physical chemist, or by the experiments done? All mass spectrometers utilize ion beams, but the unspoken definition of an ion beam instrument is an apparatus that can be used to make quantitative physical measurements. In this regard, the capabilities of the instrumentation and the intent and training of the operator are all important factors. Whereas a mass spectrometer is often used as an identification tool through the use of mass spectral patterns, by taking advantage of the ability to easily change the kinetic energy of ions, it can also be a powerful instrument for the determination of thermodynamic data.In this article, I lay down some of the founding principles behind our use of tandem mass spectrometry, and in particular, so-called guided ion beam mass spectrometry to elucidate thermochemical information. This is achieved primarily by examining the kinetic energy dependence of endothermic ion-molecule reactions and determining their energy thresholds.Although many types of instruments have been used to perform such measurements, the link between such studies and guided ion beam techniques is a strong one. Indeed, the NIST Webbook [1] states in its section on Determinations of Reaction Endothermicity that "more commonly a so-called guided-beam apparatus is utilized for such determinations." Considering that there are only about a dozen such laboratories worldwide, this is a testament to the ability of this particular kind of apparatus to provide a plethora of high quality information. However, such information requires attention to myriad details, which are outlined in this article.Two fundamental types of reactions can be used to acquire thermodynamic information: Bimolecular exchange reactions, process 1, and collision-induced dissociation (CID), process 2.Reactions 1 can be either ex...

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Dynamics of Endoergic Bimolecular Proton Transfer Reactions: F^-+ ROH → HF + RO^-(R = H, CH₃, CH₃CH₂, (CH₃)₂CH, and (CH₃)₃C)

Cited by 24 publications

References 83 publications

Absolute Rate Calculations: Atom and Proton Transfers in Hydrogen‐Bonded Systems

Absolute Rate Calculations: Atom and Proton Transfers in Hydrogen‐Bonded Systems

Competitive Threshold Collision-Induced Dissociation: Gas-Phase Acidities and Bond Dissociation Energies for a Series of Alcohols

Mass spectrometry—Not just a structural tool: The use of guided ion beam tandem mass spectrometry to determine thermochemistry

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