DFT study of the hydrogen bond strength and IR spectra of formic, oxalic, glyoxylic and pyruvic acids in vacuum, acetone and water solution

Abstract

DFT study of the hydrogen bond strength and IR spectra of formic, oxalic, glyoxylic and pyruvic acids in vacuum, acetone and water solution Giuseppe Buemi a * The molecular geometries of the possible conformations of formic, oxalic, glyoxylic and pyruvic acids have been fully optimized at DFT B3LYP/6-311RRG(d,p) levels of calculation in vacuum as well as in water and acetone solution. Solutions were treated according to the SCRF PCM approach but some formic acid-water and formic acid-acetone clusters as well as adducts of oxalic acid with two or four water molecules were also taken into account for testing the importance of specific solute-solvent effects. All the most stable isomers of the title compounds are characterized by weak intramolecular hydrogen bonds, whose strengths (E HB ) cannot be correctly estimated as stability difference between the open and chelate forms since the energy of the former isomer is, in turn, stabilized by a weak hydrogen bridge due to the formic acid moiety. Following the Rotation Barrier Method (RBM), proposed some years ago, E HB in the examined molecules (gas phase) falls in the range of 18-22 kJ/mol for oxalic acid (9.6 kJ/mol for the c-C-t isomer), 16.8 kJ/mol for glyoxylic acid and 19.8 kJ/mol for pyruvic acid. Most of them disappear at all, or nearly at all, both in acetone and aqueous solution, in consequence of the solvent effect. The frequencies of the OH and C --O stretching modes, calculated according to the anharmonic oscillator model, are in very good agreement with the experimental literature data, where available.Specific solvent effects can be obtained by considering the adduct with at least one solvent molecule. Figure 2 shows the lowest energy hydrogen bonded complexes formed by trans-and

Predicting hydration free energies using all-atom molecular dynamics simulations and multiple starting conformations

“…Without including these contributions for carboxylic acids, RMS errors would have been up to 2.45 kcal/mol depending on starting conformation for a b 2 kT), not too far off from the 7 kT observed here for ibuprofen. The ab initio calculations also found the energetic barrier for reorienting the hydroxyl is substantial, in the neighborhood of 13.3 kcal/mol [5].…”

Communication: Remarkable electrophilicity of the oxalic acid monomer: An anion photoelectron spectroscopy and theoretical study

“…Indeed, the gas phase structure of the neutral OA monomer has been studied by electron diffraction, 13 infrared and Raman spectroscopy, 13,14 matrix-isolation, [15][16][17] UV absorption, 18 microwave spectroscopy, 19 and theoretically at various levels of theory. [20][21][22][23][24][25] Here, we report a photoelectron spectrum (PES) of the OA monomer anion, which reveals a significant electrophilicity of the neutral; where the main spectral features extend from 0.5 to 2.5 eV (Figure 2). Our computational results provide an interpretation of this well-resolved photoelectron spectrum.…”

“…These minimum energy structures differ in the extent of intramolec- [13][14][15][16][17][18][19] and computational [20][21][22][23][24][25] groups. Indeed, the gas phase structure of the neutral OA monomer has been studied by electron diffraction, 13 infrared and Raman spectroscopy, 13,14 matrix-isolation, [15][16][17] UV absorption, 18 microwave spectroscopy, 19 and theoretically at various levels of theory.…”

Understanding the catalytic role of oxalic acid in the SO<sub>3</sub> hydration to form H<sub>2</sub>SO<sub>4</sub> in the atmosphere

“…As is known, oxalic acid can exist in several conformational forms (Buemi, 2009), which can be identified through the nomenclature used by Niemen et al (Nieminen et al, 1992). Thus, five stable conformers of oxalic acid were considered in this work.…”