A detailed kinetic study on the tautomerization reactions of barbituric acid: A combined DFT-QTAIM analysis

Abstract

A detailed kinetic study on the tautomerization reactions of barbituric acid (BA) at elevated temperatures from 270 K up to 1000 K was performed in this work. The B3LYP/6-311 + G(3df,2p) density functional theory (DFT) calculations were performed to evaluate the rate constants of transition states (TS) conversions of the tautomerization reactions. The connections from a given TS to the corresponding local minima of the reactant and product sides were confirmed by means of employing the intrinsic reaction coordinate (IRC) method. Moreover, the quantum theory of atoms in molecules (QTAIM) approach was employed to analyze the molecular mechanisms of reactions. The effects of vibrational normal mode frequencies of the reactant and TS were investigated on the curvature of the corresponding Arrhenius plot in the presence and absence of the tunneling effect. For each tautomerization reaction, the investigated reaction was partitioned into three different stages and four zones. The obtained results were plotted along with the corresponding reaction coordinates for each reaction considering and comparing different factors in agreement with already affirmed concepts. As a consequence, details of performed kinetic study on the tautomerization reactions of BA were successfully provided in this work.