A brief review of Badger–Bauer rule and its validation from a first-principles approach

Understanding the acid-base interactions is important in chemistry, biology and material science as it helps to rationalize materials properties such as interfacial properties, wetting, adhesion and adsorption. Quantitative relation between changes in enthalpy (ΔH) and frequency shift (Δν) during the acid-base complexation is particularly important. We investigate ΔH and Δν of twenty-five complexes of acids (methanol, ethanol, propanol, butanol and phenol) with bases (benzene, pyridine, DMSO, Et 2 O and THF) in CCl 4 using intermolecular perturbation theory calculations. ΔH and Δν of complexes of all alcohols with bases except benzene fall in the range from -14 kJ mol-1 to -30 kJ mol-1 and 215 cm-1 to 523 cm-1, respectively. Smaller values of ΔH (-2 kJ mol-1 to -6 kJ mol-1) and Δν (23 cm-1 to 70 cm-1) are estimated for benzene. Linear correlations are found between theoretical and experimental values of ΔH as well as Δν. For all the studied complexes, ΔH varies linearly (R2 ≥ 0.97) with Δν concurrent with the Badger–Bauer rule yielding the average slope and intercept of 0.053(± 0.002) kJ mol-1 cm and 2.15(± 0.56) kJ mol-1, respectively.

Development of additive isotropic site potential for exchange-repulsion energy, based on intermolecular perturbation theory

We have developed an additive spherical site potential for exchange-repulsion energy by applying the local density approximation in Hilbert space, the local-site approximation, and the s-type auxiliary basis set to the equation derived from intermolecular perturbation theory. The method efficiently addresses the decomposition of molecular interactions derived from quantum chemistry into additive spherical site potentials, required as force field input in a statistical-mechanical, reference interaction site model (RISM and 3D-RISM), molecular theory of solvation. The present method reproduces the exchange-repulsion energy between simple molecules obtained from quantum chemical calculations.

Interaction geometries and energies of hydrogen bonds to C=O and C=S acceptors: a comparative study

The occurrence, geometries and energies of hydrogen bonds from N—H and O—H donors to the S acceptors of thiourea derivatives, thioamides and thiones are compared with data for their O analogues – ureas, amides and ketones. Geometrical data derived from the Cambridge Structural Database indicate that hydrogen bonds to the C=S acceptors are much weaker than those to their C=O counterparts: van der Waals normalized hydrogen bonds to O are shorter than those to S by ∼ 0.25 Å. Further, the directionality of the approach of the hydrogen bond with respect to S, defined by the C=S...H angle, is in the range 102–109°, much lower than the analogous C=O...H angle which lies in the range 127–140°. Ab initio calculations using intermolecular perturbation theory show good agreement with the experimental results: the differences in hydrogen-bond directionality are closely reproduced, and the interaction energies of hydrogen bonds to S are consistently weaker than those to O, by ∼ 12 kJ mol−1, for each of the three compound classes. There are no CSD examples of hydrogen bonds to aliphatic thiones, (Csp 3)2C=S, consistent with the near-equality of the electronegativities of C and S. Thioureas and thioamides have electron-rich N substituents replacing the Csp 3 atoms. Electron delocalization involving C=S and the N lone pairs then induces a significant >Cδ+=Sδ− dipole, which enables the formation of the medium-strength C=S...H bonds observed in thioureas and thioamides.

Dipolar C[triple-bond]N...C[triple-bond]N interactions in organic crystal structures: database analysis and calculation of interaction energies

The Cambridge Structural Database (CSD) has been used to study nonbonded interactions between dipolar cyano groups. The analysis shows that C[triple-bond]N...C[triple-bond]N interactions form in an analogous manner to those involving carbonyl groups, and with the same interaction motifs: a dominant antiparallel dimer (57.5%) together with smaller populations of perpendicular (19.4%) and sheared parallel (23.0%) motifs. Ab initio calculations using intermolecular perturbation theory (IMPT) show an attractive C[triple-bond]N...C[triple-bond]N interaction in the dominant antiparallel dimer, with E t = −20.0 kJ mol−1 at d(C...N) = 3.30 Å and with the motif having a shear angle close to 102°. The antiparallel C[triple-bond]N...C[triple-bond]N interaction is therefore slightly weaker than the analogous C=O...C=O dimer (−23.5 kJ mol−1), but both interactions have attractive energies similar to that of a medium-strength hydrogen bond and, where sterically favoured, they are important in the stabilization of extended crystal structures.

On the Structure and Physical Origin of the Weak Interaction Between H and CO

The adiabatic potential energy surface of the H-CO complex in the van der Waals region, described by Jacobi coordinates (r = 1.128 Å, R, Θ), was investigated using the supermolecular coupled-clusters CCSD(T) method. Our calculations indicate a minimum for bent arrangements. It was found on the carbon side of CO molecule at R = 3.6 Å (Θ = 76°) with a well depth of De = -156.5 μEh. The saddle points are localised at linear conformations for R = 4.37 Å (Θ = 0°) and R = 3.91 Å (Θ = 180°). The physical origin of the studied interaction was analysed by the intermolecular perturbation theory based on the single-determinant unrestricted Hartree-Fock wave function. The separation of the interaction energies shows that the locations of the predicted stable bent structure is primarily determined by delicate balance between the repulsive Heitler-London and attractive dispersion and induction energy components.