The mechanism of double proton transfer in dimers of uracil and 2‐thiouracil—The reaction force perspective

Abstract

The intermolecular double proton transfer in dimers of uracil and 2-thiouracil is studied through density functional theory calculations. The reaction force framework provides the basis for characterizing the mechanism that in all cases has been associated to a dynamic balance between polarization and charge transfer effects. It has been found that the barriers for proton transfer depend upon the nature of the acceptor atoms and its position within the seminal monomer. Actually, the change in the nature of the hydrogen bonds connecting the two monomers along the reaction coordinate may favor or disfavor the double-proton transfer.

Insight into the Mechanism of the Michael Reaction

“…Bond breaking/forming and electronic activity along the IRC are studied in this work through a number of approaches: we follow Wiberg bond indices, their derivatives, the reaction electron flux (REF), as well as several quantities derived from topological analyses of the electron densities within Bader's quantum theory of atoms in molecules (QTAIM) formalism; in addition, we offer a view of orbital interactions and relate the propensity to nucleophilic attack at specific sites to the appropriate Fukui function. The REF represented by J ( ξ ) is defined as the negative of the derivative of the chemical potential along the reaction coordinate . The chemical potential μ ( ξ ) characterizes the tendency of electrons to escape from systems in equilibrium and is estimated here by using the energies of the frontier orbitals, which are related to the ionization potentials ( I ) and electron affinities ( A ) by Koopmans’ theorem; both quantities are calculated at each point on the IRC as [Eq.…”

“…The REF represented by J(x)i sd efined as the negative of the derivative of the chemical potential along the reaction coordinate. [53][54][55][56][57] The chemical potential m(x)c haracterizes the tendency of electrons to escape from systems in equilibrium and is estimated here by using the energies of the frontier orbitals, which are related to the ionization potentials (I)and electron affinities (A)byKoopmans' theorem; both quantities are calculated at each point on the IRC as [Eq. (5)]: [58,59]…”

Effects of the ionization in the tautomerism of uracil: A reaction electronic flux perspective

“…The reaction force analysis has been shown to offer interesting insights into many chemical reactions and in particular into hydrogen and proton transfer processes . This formalism is based on the fact that in an elementary reaction, the lowest energy path connecting reactants and products when projected into the intrinsic reaction coordinate (IRC) typically presents a maximum corresponding to the transition state (TS) connecting reactants and products.…”

New insights into the gas-phase unimolecular fragmentations of [Cysteine–Ca]2+ complexes

“…A chemical reaction can be understood in terms of geometrical changes of the molecular structures and reordering of the electron densities involved in the process and can be analyzed in terms of the reaction force concept [24][25][26] which permits to define regions where specific atomic or molecular interactions are taking place during the reaction [27,28].…”