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

Abstract

The one-step tautomerization processes of uracil and its radical cation and radical anion have been investigated in the light of the reaction force and reaction electronic flux (REF) formalisms. The relative energies of the different tautomers as well as the corresponding tautomerization barriers have been obtained through the use of the G4 high-level ab initio method and by means of B3LYP/6-311+G(3df,2p)//B3LYP/6-311+G(d, p) calculations. Systematically, the enol radical cations are more stable in relative terms than the neutral, due to the higher ionization energy of the diketo forms with respect to the enolic ones. Conversely, the enol radical anions, with the only exception of the 2-keto-N1 anion, are found to be less stable than the neutral. The effects of the ionization are also sizable on the tautomerization barriers although this effect also depends on the particular tautomerization process. The reaction force analysis shows that all reactions are mainly activated through structural rearrangements that initiate the electronic activity. This electronic activity is monitored along the reaction coordinate through the REF that obeys a delicate balance between the acid and basic character of the atoms involved in the hydrogen transfer.

Photo-ionization Initiated Differential Ultrafast Charge Migration: Impact of Molecular Symmetries and Tautomeric Forms

“…2(a)) and 8.52 eV for enol (Fig. 2(b)) and are in close agreement with previously reported values: 9.20 eV (from experiment) [33] and 8.91 eV (obtained by G4, a high-level ab initio method) [34], respectively.…”

Mechanism for Intramolecular Proton Transfer in the Isomerization of Hydroxyacetone: A Detailed Characterization Based on Reaction Force Analysis and the Bond Fragility Spectrum

“…[48][49][50][51] Collectively, these properties represent a powerful toolkit for analyzing chemical reaction mechanisms and has been demonstrated in numerous studies. [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71] The reaction force constant particularly has proven useful as an indicator of the synchronous/asynchronous nature of bond breaking/formation, it has been applied extensively to study synchronicity in Diels-Alder reactions. [72,73] Additionally, a recent method developed by Piotr Ordon and coworkers called the bond fragility spectrum aims to analyze the sequence of bond breaking/formation for a reaction by investigating the derivative of properties based on the molecular Hessian.…”

Symmetry-Adapted Perturbation Theory Decomposition of the Reaction Force: Insights into Substituent Effects Involved in Hemiacetal Formation Mechanisms

“…Fundamentally, the reaction force allows for a practical partitioning of the reaction coordinate into three regions (shown visually in Figure ): (1) a reactant region associated with geometrical changes necessary to form the transition state (TS) structure, (2) the TS region associated with the reorganization of the electron density, and (3) the product region associated with the geometrical relaxation of the TS to form the final product. This general framework for partitioning the reaction inspired further developments, leading to investigation of the second energy derivative along the IRC known as the reaction force constant , as well as the derivative of the electronic chemical potential known as the reaction electronic flux. − Together, these properties have been proven useful in providing new chemical insight in a wide variety of reaction mechanisms. − …”