Thermochemical parameters for organic radicals and radical ions. Part 2. The protonation of hydrocarbon radicals in the gas phase

1982 ◽  
Vol 60 (24) ◽  
pp. 3011-3018 ◽  
Author(s):  
A. Martin de P. Nicholas ◽  
Russell J. Boyd ◽  
Donald R. Arnold
Keyword(s):  
Gas Phase ◽  
Proton Affinity ◽  
Radical Cation ◽  
Radical Cations ◽  
Basis Sets ◽  
Thermochemical Cycle ◽  
Hydrocarbon Radical ◽  
Proton Affinities ◽  
Hartree Fock ◽  
Conjugate Base

A thermochemical cycle is used to estimate the gas phase acidity of several hydrocarbon radical cations: hydrocarbon radical cation (pKa), methane (≥ 86.5 ± 1), ethane(101 ± 1, 102 + 1), ethylene (≥ 125 ± 2), acetylene (118 ± 3, 122 ± 1), propene(124 ± 1, 122 ± 1), cyclopropane (≥ 134, ≥ 131), benzene (147 ± 1), and toluene (139 ± 1, 140). Similarly, proton affinities of the conjugate base, the hydrocarbon radical, are estimated.An estimate of the proton affinity is obtained using abinitio MO calculations. A Hartree–Fock proton affinity, PAHF(R•)g is defined as the difference in the computed energies of a radical cation and its conjugate base at the Hartree–Fock level. Calculations at the SCF level are carried out using both the minimal (STO-3G) and extended basis sets, without (3-21G, 4-31G, and 6-31G) and with (4-31G* and 6-31G*) polarization functions on carbon.The agreement between the thermochemical and abinitio estimates of the proton affinity is satisfactory.

Experimental determination of the gas phase proton affinities of the conjugate base anions of 2-iodoxybenzoic acid (IBX) and 2-iodosobenzoic acid (IBA)

2008 ◽  
Vol 6 (14) ◽  
pp. 2530 ◽  
Author(s):  
Tom Waters ◽  
Jack Boulton ◽  
Timothy Clark ◽  
Michael J. Gallen ◽  
Craig M. Williams ◽  
...  
Keyword(s):  
Experimental Determination ◽  
Gas Phase ◽  
Proton Affinities ◽  
Iodosobenzoic Acid ◽  
Conjugate Base

scholarly journals Vibrational spectra of aniline in gas phase: An ab-initio study

2010 ◽  
Vol 7 (2) ◽  
pp. 449-455
Author(s):  
S. D. S. Chauhan ◽  
A.K. Sharma ◽  
R. Kumar ◽  
D. Kulshreshtha ◽  
R. Gupta ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Gas Phase ◽  
Density Functional ◽  
Basis Set ◽  
Basis Sets ◽  
Ab Initio Study ◽  
Functional Theory ◽  
Hartree Fock ◽  
Modes Of Vibration ◽  
Experimental Findings

Vibrational frequencies of aniline in gas phase have been calculated and each of their modes of vibration assigned properly at RHF and DFT with 6-31G(d) basis set. In the present study, it has been observed that the 6-31G(d) basis set at both RHF and DFT levels of calculations provides better agreement to the experimental findings as compared to other basis sets. Simultaneously, Density functional theory is found to be superior to its counterpart Hartree Fock method.

Hydrogen atom transfer in the radical cations of tryptophan-containing peptides AW and WA studied by mass spectrometry, infrared multiple-photon dissociation spectroscopy, and theoretical calculations

2018 ◽  
Vol 25 (1) ◽  
pp. 112-121 ◽  
Author(s):  
Andrii Piatkivskyi ◽  
Justin Kai-Chi Lau ◽  
Giel Berden ◽  
Jos Oomens ◽  
Alan C Hopkinson ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Gas Phase ◽  
Radical Cation ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Radical Cations ◽  
Hydrogen Atom Transfer ◽  
Collision Induced Dissociation ◽  
Infrared Multiple Photon Dissociation ◽  
Nitrogen Radical

Two types of radical cations of tryptophan—the π-radical cation and the protonated tryptophan-N radical—have been studied in dipeptides AW and WA. The π-radical cation produced by removal of an electron during collision-induced dissociation of a ternary Cu(II) complex was only observed for the AW peptide. In the case of WA, only the ion corresponding to the loss of ammonia, [WA–NH3] •+, was observed from the copper complex. Both protonated tryptophan-N radicals were produced by N-nitrosylation of the neutral peptides followed by transfer to the gas phase via electrospray ionization and subsequent collision-induced dissociation. The regiospecifically formed N• species were characterized by infrared multiple-photon dissociation spectroscopy which revealed that the WA tryptophan-N• radical remains the nitrogen radical, while the AW nitrogen radical rearranges into the π-radical cation. These findings are supported by the density functional theory calculations that suggest a relatively high barrier for the radical rearrangement (N• to π) in WA (156.3 kJ mol−1) and a very low barrier in AW (6.1 kJ mol−1). The facile hydrogen atom migration in the AW system is also supported by the collision-induced dissociation of the tryptophan-N radical species that produces fragments characteristic of the tryptophan π-radical cation. Gas-phase ion–molecule reactions with n-propyl thiol have also been used to differentiate between the π-radical cations (react by hydrogen abstraction) and the tryptophan-N• species (unreactive) of AW.

A theoretical study of the gas phase (proton affinity) and aqueous (pKa) basicity of a series of 150 pyrazoles

2015 ◽  
Vol 39 (4) ◽  
pp. 2861-2871 ◽  
Author(s):  
Marta Marín-Luna ◽  
Ibon Alkorta ◽  
José Elguero
Keyword(s):  
Gas Phase ◽  
Proton Affinity ◽  
Theoretical Study ◽  
Proton Affinities ◽  
Aqueous Pka

Experimental proton affinities and pKas covering a range of 208 kJ mol−1 and 10.3 pKa units, respectively, have been analyzed theoretically.

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