Studies of the dynamics around the O–O bond: Orthogonal local modes of hydrogen peroxide

Theoretical Investigation on H2O2-Ng (He, Ne, Ar, Kr, Xe, and Rn) Complexes Suitable for Stereodynamics: Interactions and Thermal Chiral Rate Consequences

Although molecular collisions of noble gases (Ng) can be theoretically used to distinguish between the enantiomers of hydrogen peroxide - H₂O₂ (HP), little is known about the effects of HP-Ng interactions on the chiral rate. In this work, the chiral rate as a function of temperature (CRT) between enantiomeric conformations of HP and Ng (Ng=He, Ne, Ar, Kr, Xe, and Rn) are presented at MP2(full)/aug-cc-pVTZ level of theory through a fully basis set superposition error (BSSE) corrected potential energy surface. The results show that: (a) the CRT is highly affected even at a small decrease in the height of trans-barrier; (b) its smallest values occur with Ne for all temperatures between 100 and 4,000 K; (c) that the decrease of CRT shows an inverse correlation with respect to the average valence electron energy of the Ng and (d) Ne and He may be the noble gases more suitable for study the oriented collision dynamics of HP. In addition to binding energies, the electron density ρ and its Laplacian ∇²ρ topological analyses were also performed within the atoms in molecules (AIM) theory in order to determine the nature of the HP-Ng interactions. The results of this work provide a more complete foundation on experiments to study HP's chirality using Ng in crossed molecular beams without a light source.

A Simple Additive Potential Model for Simulating Hydrogen Peroxide in Chemical and Biological Systems

Hydrogen peroxide (H₂O₂) has numerous industrial, environmental, medical, cosmetic, and biological applications. Given its importance, we provide a simple model as an alternative to experiment for studying the properties of pure liquid H₂O₂ and its concentrated aqueous solutions, which are hazardous, and for understanding the biological roles of H₂O₂ at the molecular level. A four-site additive model is calibrated for H₂O₂ based on the ab initio and experimental properties of the gaseous monomer and the density and heat of vaporization of liquid H₂O₂ at 0 °C. Our model together with the TIP3P water model reproduce the ab initio binding energies of (H₂O₂) _m, H₂O₂· nH₂O, and nH₂O₂·H₂O clusters ( m = 2, 3 and n = 1, 2) calculated at the MP2 level using the 6-311++G(d,p) or the 6-311++G(3df,3pd) basis set. It yields structure, the self-diffusion coefficient, heat capacity, and densities at temperatures up to 200 °C of the pure liquid in good agreement with experiment. The model correctly predicts the hydration free energy of H₂O₂ and reproduces the experimental density of aqueous H₂O₂ solutions at 0-96 °C. Investigation of the solvation of H₂O₂ and H₂O in aqueous H₂O₂ solutions reveals that, as in the gas phase, H₂O₂ is a better H-bond donor but poorer acceptor than H₂O and the bonding stability follows the order O_p-H_p···O_w > O_w-H_w···O_w ≥ O_p-H_p···O_p > O_w-H_w···O_p. Stronger H-bonding in H₂O/H₂O₂ mixtures than in the pure liquids is consistent with exothermic heats of mixing and explains why the observed density and vapor pressure of the aqueous solutions are higher and lower, respectively, than expected from ideal mixing. Results also show that H₂O₂ adopts a skewed equilibrium geometry in gas and liquid phases but more polar cis and nonpolar trans conformations also are accessible and will stabilize H₂O₂ in environments of different polarity. In sum, our simple model presents a reliable tool for simulating H₂O₂ in chemistry and biology.

The gas-phase structure of dimethyl peroxide

To understand the spectroscopic properties of a molecule that performs large-amplitude motion, distinction must be made between the statical and dynamical structures.

Chirality of weakly bound complexes: the potential energy surfaces for the hydrogen-peroxide-noble-gas interactions

We consider the analytical representation of the potential energy surfaces of relevance for the intermolecular dynamics of weakly bound complexes of chiral molecules. In this paper we study the H2O2-Ng (Ng=He, Ne, Ar, Kr, and Xe) systems providing the radial and the angular dependence of the potential energy surface on the relative position of the Ng atom. We accomplish this by introducing an analytical representation which is able to fit the ab initio energies of these complexes in a wide range of geometries. Our analysis sheds light on the role that the enantiomeric forms and the symmetry of the H2O2 molecule play on the resulting barriers and equilibrium geometries. The proposed theoretical framework is useful to study the dynamics of the H2O2 molecule, or other systems involving O-O and S-S bonds, interacting by non-covalent forces with atoms or molecules and to understand how the relative orientation of the O-H bonds changes along collisional events that may lead to a hydrogen bond formation or even to selectivity in chemical reactions.

Quantum chemistry of C(3)H(6)O molecules: structure and stability, isomerization pathways, and chirality changing mechanisms

Electronic structure calculations were carried out to study the various isomers of formula C(3)H(6)O, as a part of our current quantum chemical and dynamical approaches to intra- and intermolecular kinetics for the C(n)H(2n)O (n = 1, 2, 3) molecules. The usefulness of the GRRM (global reaction route mapping) program developed by Ohno and Maeda in predicting the structure of all isomers and of the transition states connecting them is fully exploited. All the isomers are identified as local minima on the MP2/CC-PVDZ potential energy surface. Acetone is the most stable isomer. In increasing order of stability the others are propanal, 2-propenol, 1-propenol, allyl alcohol, methyl vinyl ether, cyclopropanol, propylene oxide, and oxetane. Various isomerization paths connecting them are identified. All the transition states are fully characterized using intrinsic reaction coordinate calculations. The isomerization reactions may proceed through a single step or involve an intermediate species which is either a carbene or a diradical. Special attention is devoted to propylene oxide, a favorite molecule in current photochemical and stereodynamical studies because of its chiral nature. It is a rigid molecule, and chirality switching is found to be supported by its isomers. Two different chirality switching mechanisms which are assisted by propanal and allyl alcohol are presented.

Orthogonal coordinates and hyperquantization algorithm. The NH3 and H3O+ umbrella inversion levels

In order to describe the umbrella inversion mode, which is characteristic of AB(3)-type molecules, we have introduced an alternative hyperspherical coordinate set based on a parametrization of Radau-Smith orthogonal vectors and have considered constraints which allow us to enforce the C(3v) symmetry. Structural properties and electronic energies at equilibrium and barrier configurations have been obtained at MP2 and CCSD(T) levels of theory. Energy profiles have been calculated using the CCSD(T) method with an aug-cc-pVQZ basis set. The NH(3) and H(3)O(+) umbrella inversion levels are obtained by the hyperquantization algorithm for a one-dimensional calculation, using a specially defined hyperangle as the inversion coordinate. The results are compared with experimental and theoretical energy levels, in particular, with those obtained by calculations based on two-dimensional models. The emerging picture of the umbrella inversion based on this hyperangular coordinate compares favorably with respect to the usual valence-type description.