title: Theoretical description of hydrogen bonding in oxalic acid dimer and trimer based on the combined extended-transition-state energy decomposition analysis and natural orbitals for chemical valence (ETS-NOCV).
abstract: In the present study we have analyzed hydrogen bonding in dimer and trimer of oxalic acid, based on a recently proposed charge and energy decomposition scheme (ETS-NOCV). In the case of a dimer, two conformations, α and β, were considered. The deformation density contributions originating from NOCV's revealed that the formation of hydrogen bonding is associated with the electronic charge deformation in both the σ-(Δρ(σ)) and π-networks (Δρ(π)). It was demonstrated that σ-donation is realized by electron transfer from the lone pair of oxygen on one monomer into the empty P*(H-O) orbital of the second oxalic acid fragment. In addition, a covalent contribution is observed by the density transfer from hydrogen of H-O group in one oxalic acid monomer to the oxygen atom of the second fragment. The resonance assisted component (Δρ(π)), is based on the transfer of electron density from the π-orbital localized on the oxygen of OH on one oxalic acid monomer to the oxygen atom of the other fragment. ETS-NOCV allowed to conclude that the σ(O---HO) component is roughly eight times as important as π (RAHB) contribution in terms of energetic estimation. The electrostatic factor (ΔE(elstat)) is equally as important as orbital interaction term (ΔE(orb)). Finally, comparing β-dimer of oxalic acid with trimer we found practically no difference concerning each of the O---HO bonds, neither qualitative nor quantitative.
authors.affiliation: Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University, R.Ingardena 3, 30-060, Cracow, Poland.
authors.forename: Mariusz P
authors.initials: MP
authors.lastname: Mitoraj
authors.forename: Rafał
authors.initials: R
authors.lastname: Kurczab
authors.forename: Marek
authors.initials: M
authors.lastname: Boczar
authors.forename: Artur
authors.initials: A
authors.lastname: Michalak
mesh_terms: D019281:Dimerization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D019815:Oxalic Acid / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D019815:Oxalic Acid