Comprehensive Empirical Model of Substitution-Influence on Hydrogen Bonding in Aromatic Schiff Bases.

In this work, over 500 structures of tri-ring aromatic Schiff bases with different substitution patterns were investigated to develop a unified description of the substituent effect on the intramolecular hydrogen bridge. Both proximal and distal effects were examined using Density Functional Theory (DFT) in the gas phase and with solvent reaction field (Polarizable Continuum Model (PCM) and water as the solvent). In order to investigate and characterize the non-covalent interactions, a topological analysis was performed using the Quantum Theory of Atoms In Molecules (QTAIM) theory and Non-Covalent Interactions (NCI) index. The obtained results were summarized as the generalized, empirical model of the composite substituent effect, assessed using an additional group of simple ring-based Schiff bases. The composite substituent effect has been divided into separate increments describing the different interactions of the hydrogen bridge and the substituent: the classical substituent effect, involving resonance and induction mediated through the ring, steric increment based on substituent proximity to the bridge elements, and distal increment, derived from substitution on the distal ring.

Inside out Approach to Rotator State in Hydrogen-Bonded System-Experimental and Theoretical Cross-Examination in n-Octanol.

The experimental and theoretical description of premelting behavior is one of the most challenging tasks in contemporary material science. In this paper, n-octanol was studied using a multi-method approach to investigate it at macroscopic and molecular levels. The experimental infrared (IR) spectra were collected in the solid state and liquid phase at temperature range from -84∘C to -15 ∘C to detect temperature-related indicators of pretransitional phenomena. Next, the nonlinear dielectric effect (NDE) was measured at various temperatures (from -30 ∘C to -15 ∘C) to provide insight into macroscopic effects of premelting. As a result, a two-step mechanism of premelting in n-octanol was established based on experimental data. It was postulated that it consists of a rotator state formation followed by the surface premelting. In order to shed light onto molecular-level processes, classical molecular dynamics (MD) was performed to investigate the time evolution of the changes in metric parameters as a function of simulation temperature. The applied protocol enabled simulations in the solid state as well as in the liquid (the collapse of the ordered crystal structure). The exact molecular motions contributing to the rotator state formation were obtained, revealing an enabling of the rotational freedom of the terminal parts of the chains. The Car-Parrinello molecular dynamics (CPMD) was applied to support and interpret experimental spectroscopic findings. The vibrational properties of the stretching of OH within the intermolecular hydrogen bond were studied using Fourier transformation of the autocorrelation function of both dipole moments and atomic velocity. Finally, path integral molecular dynamics (PIMD) was carried out to analyze the quantum effect's influence on the bridged proton position in the hydrogen bridge. On the basis of the combined experimental and theoretical conclusions, a novel mechanism of the bridged protons dynamics has been postulated-the interlamellar hydrogen bonding pattern, resulting in an additional OH stretching band, visible in the solid-state experimental IR spectra.

Intermolecular Interactions and Spectroscopic Signatures of the Hydrogen-Bonded System-n-Octanol in Experimental and Theoretical Studies.

n-Octanol is the object of experimental and theoretical study of spectroscopic signatures and intermolecular interactions. The FTIR measurements were carried out at 293 K for n-octanol and its deuterated form. Special attention was paid to the vibrational features associated with the O-H stretching and the isotope effect. Density Functional Theory (DFT) in its classical formulations was applied to develop static models describing intermolecular hydrogen bond (HB) and isotope effect in the gas phase and using solvent reaction field reproduced by Polarizable Continuum Model (PCM). The Atoms in Molecules (AIM) theory enabled electronic structure and molecular topology study. The Symmetry-Adapted Perturbation Theory (SAPT) was used for energy decomposition in the dimers of n-octanol. Finally, time-evolution methods, namely classical molecular dynamics (MD) and Car-Parrinello Molecular Dynamics (CPMD) were employed to shed light onto dynamical nature of liquid n-octanol with emphasis put on metric and vibrational features. As a reference, CPMD gas phase results were applied. Nuclear quantum effects were included using Path Integral Molecular Dynamics (PIMD) and a posteriori method by solving vibrational Schrödinger equation. The latter applied procedure allowed to study the deuterium isotope effect.