Predicting Mole‐Fraction‐Dependent Dissociation for Weak Acids

Abstract

We demonstrate for formic and acetic acid dissolved in water as examples that the binary quantum cluster equilibrium (bQCE) approach can predict acid strengths over the whole range of acid concentrations. The acid strength increases in a complex rather than a simple way with increasing mole fraction of the acid from 0 to 0.7, reflecting the complex interplay between the dissociated ions or conjugate bases available as compared to the acid and water molecules. Furthermore, our calculated ion concentrations meet the experimental maximum of the conductivity with excellent agreement for acetic acid and satisfactorily for the formic acid/water mixture. As only a limited number of simple quantum‐chemical calculations are required for the prediction, bQCE is clearly a valuable approach to access these quantities also in non‐aqueous solutions. It is a highly valuable asset for predicting ionization processes in highly concentrated solutions, which are relevant for biological and chemical systems, as well as technological processes.

Predicting Vibrational Spectroscopy for Flexible Molecules and Molecules with Non‐Idle Environments

“…Applications of the QCE method involve many neat and binary systems, including water, [4,67,68] aqueous solutions [15,69] and even ionic liquids. [70] In addition, we calculated activity coefficients [71] and ionicity [17,18,72] with binary QCE and we applied QCE or cluster weighting CW to vibrational circular dichroism [7] .…”

“…Besides the calculation of properties to which clusters of different sizes can contribute simultaneously, this method opens the door for concentration‐dependent calculations. [ 16–18 ]…”

“…Besides the calculation of properties to which clusters of different sizes can contribute simultaneously, this method opens the door for concentration-dependent calculations. [16][17][18] Apart from the static approach, we will secondly focus on ab initio molecular dynamics simulations [19] (AIMD) of a complete but "small" system. The Delle Site group showed a specific locality for the properties applied here such as the electric dipole moment, which justifies the small system size.…”

Hydrogen Bonding and Vaporization Thermodynamics in Hexafluoroisopropanol‐Acetone and ‐Methanol Mixtures. A Joined Cluster Analysis and Molecular Dynamic Study

“…wherein b xv is the empirical exclusion volume parameter to correctly scale the cluster volume , which is sensitive to the choice of the volume method and the atomic radii used therein. In previous works, b xv was treated as temperature independent [27,32,33,35,38] . Here, we introduce a linear temperature dependence of b xv …”

“…Boltzmann and bQCE weighting were compared in the past by our group in the field of the computational calculation of vibrational circular dichroism spectra of bulk phase, showing the advantages of our method over Boltzmann weighting [29] . For this purpose we use our in‐house code Peacemaker 2.8, which has proven to be a valuable tool to investigate the thermodynamic properties of both neat and mixed systems [27,30–38] . The standard bQCE method involves optimization of two empirical parameters by fitting them to a set of experimental data such as boiling points or isobars; however, even for simple mixtures of organic solvents, these data are often unavailable in the literature.…”