Determination of gas-phase acidities of dimethylphenols: Combined experimental and theoretical study

Madeira, Paulo J. Amorim; Costa, Paulo J.; Fernandez, M. Tereza; Simões, José A. Martinho; Leal, João Paulo

doi:10.1016/j.jasms.2008.06.026

Cited by 7 publications

(8 citation statements)

References 28 publications

(31 reference statements)

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“…For the self-ionization of gaseous methane, the situation is very similar to liquid-phase chemistry in which acids undergo autoprotolysis if they are pure or homoconjugation when dissolved in inert solvents. By the addition of Equations (8) and (10), the autoprotolysis equilibrium of methane is obtained [Eq. (12)]:…”

Section: Wwwchemeurjorgmentioning

confidence: 99%

“…To describe the Brønsted acidity or basicity of molecules or ions, gas-phase acidity (GA) and gas-phase basicity (GB) scales were established based on experimental [1][2][3][4][5][6][7][8][9] (e.g., Fourier transform ion cyclotron resonance (FTICR)) or quantum chemical [10][11][12][13][14][15][16][17] grounds. GA and GB are standard Gibbs reaction energies defined in Equation (1):…”

Section: Introductionmentioning

confidence: 99%

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Bulk Gas‐Phase Acidity

Himmel

Goll

Leito

et al. 2012

Chemistry A European J

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The capability of a gaseous Brønsted acid HB to deliver protons to a base is usually described by the gas-phase acidity (GA) value of the acid. However, GA values are standard Gibbs energy differences and refer to individual gas pressures of 1 bar for acid HB, base B(-), and proton H(+). We show that the GA value is not suited to describe the bulk acidity of a gaseous acid. Here the pressure dependence of the activities of HB, H(HB)(n)(+), and B(HB)(m)(-) that result from gaseous autoprotolysis have to be considered. In this work, the pressure-dependent absolute chemical potential of the proton in the representative gaseous proton acids CH(4), NH(3), H(2)O, HF, and HCl was worked out and the general theory to describe bulk gas phase acidity--that can directly be compared with solution acidity--was developed.

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Section: Wwwchemeurjorgmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Bulk Gas‐Phase Acidity

Himmel

Goll

Leito

et al. 2012

Chemistry A European J

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“…In the past years we have determined the gas-phase acidity for several substituted phenols, including dimethylphenols, (Madeira, Costa et al 2008) dimethoxyphenols and chromanol (Madeira, Faddoul et al 2011), with the purpose of establishing a bridge towards vitamin E. Fig. 19a and b depicts the negative chemical ionization mass spectrum of a mixture of 3,5-dimethylphenol and 4-methylphenol and the MS 2 spectrum of the isolated heterodimer (m/z 229).…”

Section: Gas-phase Acidities Of Substituted Phenolsmentioning

confidence: 99%

“…To note that in the case of proton affinities and gas-phase basicities the work is done in the positive ion mode while for gas-phase acidities the mass spectra are acquired in the negative ion mode. (Madeira, Costa et al 2008) Same as for the aniline derivatives presented earlier, if we pair the unknown compounds with other compounds with known gas-phase acidity we can apply the kinetic method formalism and determine its gas-phase acidity. The gas-phase acidity scales for dimethylphenols (Madeira, Costa et al 2008) and for dimethoxyphenols and chromanol (Madeira, Faddoul et al 2011) are graphically depicted in Fig.…”

Section: Gas-phase Acidities Of Substituted Phenolsmentioning

confidence: 99%

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Applications of Tandem Mass Spectrometry: From Structural Analysis to Fundamental Studies

Madeira¹,

Florêncio²

2012

Tandem Mass Spectrometry - Applications and Principles

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Can Semi‐empirical Calculations Help Solve Mass Spectrometry Problems? Protonation Sites and Proton Affinities of Amino Acids

et al. 2013

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Owing to the recent development of the PM6 and PM6‐DH+ semi‐empirical methodologies, which belong to the neglect of diatomic differential overlap (NDDO) family, it was decided to carry out a study to assess whether these inexpensive and fast methodologies could be used with confidence to help solve mass spectrometry problems. As such, a report on the feasibility of using semi‐empirical calculations to identify probable protonation sites in amino acids is presented. The optimised geometries obtained by the semi‐empirical calculations were compared to several structures reported in the literature (obtained through high‐level theoretical calculations) and reasonable agreement was found. The proton affinities derived from semi‐empirical calculations were also compared with experimental data and benchmarked as well with predicted values from the literature (also obtained through high‐level theoretical calculations). Semi‐empirical calculations accurately predicted the most probable protonation site for all amino acids considered; thus leading to results comparable to those obtained by high‐level calculations at an extremely low computational cost. Regarding the proton affinity estimates, deviations from the available experimental values are greater for the semi‐empirical proton affinities than for those observed for high‐level calculations. A statistical analysis of the data, at a confidence level of 99 %, also showed that the semi‐empirical proton affinities were different from experimental values and high‐level proton affinities were equivalent to experimental values. Nevertheless, the overall correlation of the semi‐empirical data with experimental values is, at least, satisfactory. We believe therefore that this paper shows that semi‐empirical methodologies, which are fast and inexpensive, can indeed solve mass spectrometry problems, or at least, facilitate a quicker path to the solution.

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Determination of gas-phase acidities of dimethylphenols: Combined experimental and theoretical study

Cited by 7 publications

References 28 publications

Bulk Gas‐Phase Acidity

Bulk Gas‐Phase Acidity

Applications of Tandem Mass Spectrometry: From Structural Analysis to Fundamental Studies

Can Semi‐empirical Calculations Help Solve Mass Spectrometry Problems? Protonation Sites and Proton Affinities of Amino Acids

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