Global Reaction Route Mapping Method Research Articles

Global reaction route mapping of water-catalysed gas phase oxidation of glyoxylic acid with hydroxyl radical

In order to assess the potential role of a single water molecule as a catalyst, the gas-phase oxidation reaction of hydroxyl radical with glyoxylic acid has been investigated by the means of quantum mechanical computations using CCSD(T), MP2 and DFT methods. The pre-reaction complexes along the oxidation pathways are systematically explored through a global reaction route mapping method. The computations reveal that a single water molecule stabilizes the pre-reaction complexes as well as respective transition states, resulting in the lowering of the energy barrier, however, the transition state theory computed rate constants for the water-catalysed pathways are found to be an order of magnitude lower than that for the water-free pathways. Notably, the abstraction of formyl hydrogen is observed to be most favourable both in the presence and absence of a single water molecule. Besides these, a couple of triple-proton exchange pathways involving simultaneous proton transfer between the glyoxylic acid, OH radical and a single water molecule are also explored. All the pathways are observed to proceed through conventional free radical mechanism when analysed using BHandHLYP exchange–correlation (XC) functional of DFT. However, DFT method using other XC functionals revealed that one of the relevant acidic H-abstraction pathways proceeds through a proton-coupled electron-transfer mechanism and also results in the dissociation of glyoxylic acid. The pathways for trans form of glyoxylic acid has also been compared with those explored for the cis form. The standard Gibbs free-energy profiles for the reactions studied indicate that the hydrogen abstraction, particularly in trans-glyoxylic acid, may be more feasible than the dissociation, particularly at lower temperatures. This study may assist future investigation of similar atmospheric reactions.

Automated exploration of isomerization and dissociation pathways of ethylene sulfide cation by the global reaction route mapping method

Isomerization and dissociation reaction pathways of C2H4S+ associated with photoionization of c-C2H4S have been explored on the potential energy surfaces by the global reaction route mapping (GRRM) method. Reaction channels yielding C2H3S+, HCS+, H2S+, C2H3+, and C2H2S+ were disclosed. Calculated values of energy barriers to transition states and direct dissociation energies gave theoretical supports to recent synchrotron radiation experiments generating HCS+ and C2H3S+.

Exploring the metastability and the pathways for polyanionic isomerization in the dianions and trianions of doubly- and triply-deprotonated benzene

Polyanions of the aromatic origin such as dianion of benzene (C6H6 2−) are generally metastable having negative electron affinity (EA). However, the de-protonated species of these anions such as doubly-deprotonated dianions of benzene (C6H4 2−) can have higher proton affinity compared to the magnitude of the negative EA, which can trigger an intra-molecular proton transfer besides the electron auto-detachment. Such species though may exhibit resonances as in the temporary anions and cannot be treated using the conventional variational methods of the quantum mechanics. In this work, we discuss the metastability, through a nuclear-charge stabilization method, for the poly-deprotonated dianions and trianions of benzene, while exploring the intra-molecular proton-transfer reaction pathways using the conventional quantum mechanical methods, for the isomerization between the isomeric doubly-deprotonated benzene dianions, namely the ortho-, meta-, and para-C6H4 2−, as well as between the isomeric triply-deprotonated benzene trianions, namely the 1,2,3-, 1,2,4-, and 1,3,5-C6H3 3− in their singlet state. For this, the potential energy surfaces of the polyanionic species, in particular those of the doubly-deprotonated dianions, are successfully explored through an automated and systematic search performed using the global reaction route mapping method. The computations performed at the levels of the MP2, DFT with and without dispersion, and CCSD(T) theories, identified elusive reaction pathways for the isomerization between the anionic species of the poly-deprotonated benzene. Notably, a single-step isomerization between the ortho- and para-C6H4 2− dianions is observed to proceed via a direct 1, 3-proton shift in an unconventional transition state involving a puckered benzene ring in a nearly half-boat conformation. However, for the isomerization between C6H3 3− benzene trianions, the present work was able to reveal pathway only between 1,2,4-C6H3 3− and 1,3,5-C6H3 3− trianions, indicating the problems like variational collapse inherent with the conventional methods while dealing with the molecular polyanions. However, the lifetime of the metastable molecular ions investigated in this work is estimated to be of the order of only a few femtoseconds, an order of magnitude higher than the proton-transfer rate along the proposed isomerization pathways, but this study is able to provide valuable insights into the mechanism of proton transfer in the presence of a competing electron auto-detachment process.

Diversity of the Dimer Structures of Toluene: Exploration by the GRRM Method

Abstract Quantum chemical calculations were performed to explore the equilibrium structures (EQs) of the toluene dimer using the GRRM (global reaction route mapping) method, and 23 EQs were found. 11 EQs among these exhibited only slight changes in the structure and relative order of the stability even when the structures were refined at higher calculation levels. The EQs with the largest stabilization included the interactions between a methyl C–H bond of one molecule and the π-electron system of another molecule.

Unexpected Formation of Highly Strained 2,5‐Dioxa‐3‐Silabicyclo[2.1.0]Pentane by the Reaction of Isolable Dialkylsilylene with Benzil

ABSTRACTThe reaction of isolable dialkylsilylene 1 with benzil gave [1+4] cycloadduct 1,3‐dioxa‐2‐sila‐cyclopent‐4‐ene 2 and unexpected 2,5‐dioxa‐3‐silabicyclo[2.1.0]pentane derivative 3. Compound 3 slowly isomerized to 2. The global reaction route mapping method of the model compounds suggests that three reaction paths from an initial silylene–ketone complex (carbonyl silaylide) to 2. A large ring strain energy of model compound for 3 (3′) (218.9 kJ·mol−1) was estimated by density functional theory calculations.

The mechanism of tautomerisation and geometric isomerisation in thioformic acid and its water complexes: exploring chemical pathways for water migration.

A systematic and automated search for chemical pathways of isomerisation between geometric and tautomeric forms of gas-phase thioformic acid (TFA) and its water complexes is performed using a global reaction route mapping (GRRM) method, and an uncovered pathway for cis-trans isomerisation in the thiol form of TFA has been explored through computations performed at CCSD(T)/6-311++G(2d,2p)//B3LYP/6-311++G(2d,2p) level of the coupled cluster and density functional theories. To explore the routes for water migration, a detailed analysis of complexes of TFA with a single-water molecule is presented. Notably, during the isomerisation process in TFA, a positive catalytic effect of water was observed that can arise either by the stabilization of the reactant and/or of the transition state through extensive hydrogen bonding. Interesting behavior of isomeric forms of TFA along the pathways analysed is revealed through the Gibbs free-energy change and its temperature-dependence. The cis form of TFA(thiol) in the complexes of TFA with a single-water molecule is found to be thermodynamically equally feasible as the trans form which though is known to be the most dominating among the isomeric forms of TFA. Besides these, various complexes of TFA with two-water molecules have also been explored to study the hydrogen-bonding interaction through natural bond-orbital (NBO) analysis. The complexes of TFA with two-water molecules have also been characterized using spectral features including vibrational frequency analysis, and the effect of complexation has been observed by noting frequency shift.

Global reaction route mapping of isomerization pathways of exotic C6H molecular species

C6H radical is known to exist in the astrophysical environment in linear form; however, it may originate from nonlinear isomeric forms. Potential energy surface of C6H is explored to search isomers of C6H and transition states connecting them. This work reports first-ever identification of reaction pathways for isomerization of C6H. The reaction route search is performed through global reaction route mapping method, which utilizes an uphill walking technique based on an anharmonic downward distortion following approach to search intermediates and transition states. The computations performed at the CASSCF∕aug-cc-pVTZ, CCSD(T)∕6-311++G(d,p)∕∕DFT∕B3LYP∕6-311++G(d,p), and DFT∕B3LYP∕aug-cc-pVTZ levels of the theory identified 14 isomers (including 8 new isomeric forms of C6H) and 28 transition states. Most of the identified isomers are found to have significant multireference character. The kinetic stability and natural bond orbital analysis of the identified isomers is also investigated. The isomeric forms are further characterized using spectral analysis involving rotational constants, vibrational frequencies, and Raman scattering activities as well as analyzing the effect of isotopic substitution of hydrogen on the spectral features. This study proposes that the linear-C6H can readily isomerize to a six-member ring isomer.

Ab Initio Study on Reduction Mechanisms of Vinylene Carbonate Using Global Reaction Route Mapping Method

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A systematic study on the RuHCl–BINAP-catalyzed asymmetric hydrogenation mechanism by the global reaction route mapping method

Anharmonic downward distortion (ADD) of potential energy surfaces (PES) indicates the direction of reaction routes, and the ADD-following on PES has made it possible to perform global reaction route mapping (GRRM) of a given chemical formula. The GRRM method based on the ADD-following can be applied to real processes of catalytic reactions to elucidate the reaction mechanisms. A systematic analysis of a RuHCl–BINAP-catalyzed asymmetric hydrogenation reaction has given an insight into the role of important adsorption structures and the chirality determining transition state among numerous candidates. Computed reaction profiles for the total catalytic cycles with and without protonation demonstrated significance of the protonation for both high enantioselectivity and high catalytic-activity.