Search for: All records

The generation of reference data for deep learning models is challenging for reactive systems, and more so for combustion reactions due to the extreme conditions that create radical species and alternative spin states during the combustion process. Here, we extend intrinsic reaction coordinate (IRC) calculations withab initioMD simulations and normal mode displacement calculations to more extensively cover the potential energy surface for 19 reaction channels for hydrogen combustion. A total of ∼290,000 potential energies and ∼1,270,000 nuclear force vectors are evaluated with a high quality range-separated hybrid density functional,ωB97X-V, to construct the reference data set, including transition state ensembles, for the deep learning models to study hydrogen combustion reaction.

Interfaces, the boundary that separates two or more chemical compositions and/or phases of matter, alters basic chemical and physical properties including the thermodynamics of selectivity, transition states, and pathways of chemical reactions, nucleation events and phase growth, and kinetic barriers and mechanisms for mass transport and heat transport. While progress has been made in advancing more interface‐sensitive experimental approaches, their interpretation requires new theoretical methods and models that in turn can further elaborate on the microscopic physics that make interfacial chemistry so unique compared to the bulk phase. In this review, we describe some of the most recent theoretical efforts in modeling interfaces, and what has been learned about the transport and chemical transformations that occur at the air–liquid and solid–liquid interfaces.

This article is categorized under:

Structure and Mechanism > Reaction Mechanisms and Catalysis

Understanding the bonding of gold(I) species has been central to the development of gold(I) catalysis. Herein, we present the synthesis and characterization of the first gold(I)‐cyclobutadiene complex, accompanied with bonding analysis by state‐of‐the‐art energy decomposition analysis methods. Analysis of possible coordination modes for the new species not only confirms established characteristics of gold(I) bonding, but also suggests that Pauli repulsion is a key yet hitherto overlooked element. Additionally, we obtain a new perspective on gold(I)‐bonding by comparison of the gold(I)‐cyclobutadiene to congeners stabilized by p‐, d‐, and f‐block metals. Consequently, we refine the gold(I) bonding model, with a delicate interplay of Pauli repulsion and charge transfer as the key driving force for various coordination motifs. Pauli repulsion is similarly determined as a significant interaction in Au^I‐alkyne species, corroborating this revised understanding of Au^Ibonding.

Lowering of the electron kinetic energy (KE) upon initial encounter of radical fragments has long been cited as the primary origin of the covalent chemical bond based on Ruedenberg’s pioneering analysis of H$${}_{2}^{+}$$${}_2^{+}$and H₂and presumed generalization to other bonds. This work reports KE changes during the initial encounter corresponding to bond formation for a range of different bonds; the results demand a re-evaluation of the role of the KE. Bonds between heavier elements, such as H₃C–CH₃, F–F, H₃C–OH, H₃C–SiH₃, and F–SiF₃behave in the opposite way to H$${}_{2}^{+}$$${}_2^{+}$and H₂, with KE often increasing on bringing radical fragments together (though the total energy change is substantially stabilizing). The origin of this difference is Pauli repulsion between the electrons forming the bond and core electrons. These results highlight the fundamental role of constructive quantum interference (or resonance) as the origin of chemical bonding. Differences between the interfering states distinguish one type of bond from another.

Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(OtBu)₃]₄⁻and HOM[OSi(OtBu)₃]₃⁻(where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(OtBu)₃]₃Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown‐4 afforded charge‐separated ion pairs composed of monomeric anions M[OSi(OtBu)₃]₄⁻with outer‐sphere [([12]crown‐4)₂Li]⁺cations, and hydroxides {HOM[OSi(OtBu)₃]₃} with pendant [([12]crown‐4)Li]⁺cations. These molecular models were characterized by single‐crystal X‐ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy. Upon treatment of monomeric [([12]crown‐4)Li]{HOM[OSi(OtBu)₃]₃} complexes with benzyl alcohol, benzyloxide complexes were formed, modeling a possible pathway for the formation of active sites for Meerwin–Ponndorf–Verley (MPV) transfer hydrogenations with Al/Ga‐doped silica catalysts.