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Bridged cyclobutanes and sulfur heterocycles are currently under intense investigation as building blocks for pharmaceutical drug design. Two formal cycloaddition modes involving bicyclobutanes (BCBs) and pyridinium 1,4‐zwitterionic thiolate derivatives were described to rapidly expand the chemical space of sulfur‐containing bridged cyclobutanes. By using Ni(ClO4)2 as the catalyst, an uncommon higher‐order (5+3) cycloaddition of BCBs with quinolinium 1,4‐zwitterionic thiolate was achieved with broad substrate scope under mild reaction conditions. Furthermore, the first Lewis acid‐catalyzed asymmetric polar (5+3) cycloaddition of BCB with pyridazinium 1,4‐zwitterionic thiolate was accomplished. In contrast, pyridinium 1,4‐zwitterionic thiolates undergo an Sc(OTf)3‐catalyzed formal (3+3) reaction with BCBs to generate thia‐norpinene products, which represent the initial instance of synthesizing 2‐thiabicyclo[3.1.1]heptanes (thia‐BCHeps) from BCBs. Moreover, we have successfully used this (3+3) protocol to rapidly prepare thia‐BCHeps‐substituted analogues of the bioactive molecule Pitofenone. Density functional theory (DFT) computations imply that kinetic factors govern the (5+3) cycloaddition reaction between BCB and quinolinium 1,4‐zwitterionic thiolate, whereas the (3+3) reaction involving pyridinium 1,4‐zwitterionic thiolates is under thermodynamic control. [ABSTRACT FROM AUTHOR]

This study analyzes the samarium diiodide‐promoted cyclizations of 5‐arylpentan‐2‐ones to dearomatized bicyclic products utilizing density functional theory. The reaction involves a single electron transfer to the carbonyl group, which occurs synchronously with the rate determining cyclization event, and a second subsequent proton‐coupled electron transfer. These redox reactions are accurately computed employing small core pseudo potentials explicitly involving all f‐electrons of samarium. Comparison of the energies of the possible final products rules out thermodynamic control of the observed regio‐ and diastereoselectivities. Kinetic control via appropriate transition states is correctly predicted, but to obtain reasonable energy levels the influence of the co‐solvent hexamethylphosphortriamide has to be estimated by using a correction term. The steric effect of the bulky samarium ligands is decisive for the observed stereoselectivity. Carbonyl groups in para‐position of the aryl group change the regioselectivity of the cyclization and lead to spiro compounds. The computations suggest again kinetic control of this deviating outcome. However, the standard mechanism has to be modified and the involvement of a complex activated by two SmI2 moieties is proposed in which two electrons are transferred simultaneously to form the new C−C bond. Computation of model intermediates show the feasibility of this alternative+ mechanism. [ABSTRACT FROM AUTHOR]

The metal carbonyl clusters have been recognized as one of the most successful organometallic complexes with extensive catalytic applications. In this paper, we carried out a DFT study of the stability, electronic structure and thermodynamic properties of the intermediates [M3(CO)11] and [M3(CO)10] in the synthesis of [M3(2,3-bpp)(CO)10] (M=Ru and Os). CO binding energy analysis revealed that [M3(CO)10(μ-CO)], [Ru3(CO)8(μ-CO)2] and [Os3(CO)6(μ3-CO)2(μ-CO)2] are the most stables compounds due to the presence of bridge carbonyls which favor a covalent interaction. Sigma donation from the carbonyl to metal d orbital is the most significant contribution. Moreover, spectroscopic and computational studies indicated that [Ru3(2,3-bpp)(CO)10] is in good agreement with the analogues osmium complex. Regarding the pathway associated to the formation of [M3(2,3-bpp)(CO)10] we have found that the determinant step is the dissociation of a second CO axial into [M3(CO)10(μ-CO)]. Thus, unsaturated metal carbonyl intermediates exert a thermodynamic and kinetically control as consequence of the orbital reorganization. [ABSTRACT FROM AUTHOR]

We show how to incorporate the possibility of kinetic control in the conceptual density functional theory formalism. This allow us to prove that the hard/soft acid/base principle will likely fail when the reactions are not thermodynamically-driven. [ABSTRACT FROM AUTHOR]

• Stabilities of cholestane isomers are studied with the density functional theory. • The isomeric ratios of cholestane are found to be governed thermodynamically. • The length of the side chain has little effect on the isomeric ratios. • The energy difference between isomers stems from 1,3-diaxial interactions. Cholestane is produced by diagenesis of cholesterol in the geosphere being known to have four main stereoisomers. The abundance ratios of these stereoisomers are important indicators of the geospheric thermal history. However, it has been unclear whether the isomeric ratios are caused by kinetic or thermodynamic dominance. In this study, we analyzed the isomeric ratios of cholestane under thermodynamic dominance using the density functional theory. The calculated isomeric ratios are in good agreement with the limit values in the geosphere, indicating that the isomeric ratios in the geosphere can be obtained under thermodynamic control. We also discussed the factors contributing to their stabilities. [ABSTRACT FROM AUTHOR]

Selective synthetic modifications on diamondoids (well‐defined molecular nano‐diamonds) are difficult. Group IV organometallic complexes are promising systems for CH bond activation. We study the CH bond activation of the hard‐to‐activate CH2 positions of the adamantyl group (the smallest diamondoid) using density functional theory. As a platform for activation, we tether the adamantyl group to the cyclopentadienyl in a substituted bis‐cyclopentadienyl group IV metal diphenyl complex. The mechanism proposed in the experimental paper reporting the activation of C(Me)2‐Ph or t‐Bu groups using Zr(IV) involves an η2‐benzyne complex intermediate. Our computational work confirms the two‐step mechanism proposed for activation of C(Me)2‐Ph or t‐Bu using Zr(IV) and further extends it to Ti(IV) and Hf(IV). The first step forms the benzyne complex. In the second step, the cyclopentadienyl‐bound group is activated through a mechanism that closely resembles a σ‐bond metathesis when the benzyne complex is described as a metallacyclopropene We demonstrate through computations that the two‐step reaction can be successfully applied to the adamantyl group. CH bond activation of adamantyl is found to be thermodynamically and kinetically feasible. The important question of regioselectivity is addressed. We predict that α‐CH bond activation will be achievable with Ti (thermodynamic control), and selective γ‐CH bond activation with Zr (kinetic or thermodynamic control). [ABSTRACT FROM AUTHOR]

Mono‐ and bis‐decylated lumazines have been synthesized and characterized. Namely, mono‐decyl chain [1‐decylpteridine‐2,4(1,3H)‐dione] 6a and bis‐decyl chain [1,3‐didecylpteridine‐2,4(1,3H)‐dione] 7a conjugates were synthesized by nucleophilic substitution (SN2) reactions of lumazine with 1‐iododecane in N,N‐dimethylformamide (DMF) solvent. Decyl chain coupling occurred at the N1 site and then the N3 site in a sequential manner, without DMF condensation. Molecular orbital (MO) calculations show a p‐orbital at N1 but not N3, which along with a nucleophilicity parameter (N) analysis predict alkylation at N1 in lumazine. Only after the alkylation at N1 in 6a, does a p‐orbital on N3 emerge thereby reacting with a second equivalent of 1‐iododecane to reach the dialkylated product 7a. Data from NMR (1H, 13C, HSQC, HMBC), HPLC, TLC, UV‐vis, fluorescence and density functional theory (DFT) provide evidence for the existence of mono‐decyl chain 6a and bis‐decyl chain 7a. These results differ to pterin O‐alkylations (kinetic control), where N‐alkylation of lumazine is preferred and then to dialkylation (thermodynamic control), with an avoidance of DMF solvent condensation. These findings add to the list of alkylation strategies for increasing sensitizer lipophilicity for use in photodynamic therapy. [ABSTRACT FROM AUTHOR]

A computational study on the mechanisms of reaction for the pyrolysis of asparagine is presented. A density functional theory (DFT) study at the ω B97XD/6-311G(d,p) level was performed to analyze the differences in two reaction mechanisms: (i) the formation of five-membered cyclic products: maleimide and succinimide, and (ii) the more classical, six-membered cyclic products (diketopiperazine species) which are common in the pyrolysis of many other amino acids. The effect of temperature was included in the calculations at 300 °C or 625 °C, as required. Moreover, a detailed study based on the degree of rate control and thermodynamic control of the proposed mechanism for the formation of maleimide and succinimide is also presented. Results show that, for asparagine, the five-membered ring formation is the preferred process instead of the six-membered cycle (32 kJ/mol of Gibbs free energy difference between them at the first cyclization step); therefore, the polymerization is favored. On the other hand, the rupture of the polymer represents the highest energetic barrier (ΔG‡ = 281 kJ/mol) and the most influential process in the overall rate of the reaction. These results are in good agreement with the experimental evidence. [ABSTRACT FROM AUTHOR]

The mechanism of 1,4-, 1,2-, and 3,4-cyclization reactions of cyclic 1-azadiene 1 with an organocatalyst 4 has been studied theoretically using DFT method. The reactions proceed in a stepwise fashion, with zwitterionic intermediates. The most favorable cyclization reaction takes place along the C–C pathway of the 1,4-cyclization reaction, under a combination of kinetic and thermodynamic control. The reaction is characterized by the nucleophilic attack of 4 (C5) to the electrophilic center of 1 (C1), leading to the formation of cycloadduct 6, which correctly explains the source of the regioselectivity. [ABSTRACT FROM AUTHOR]

Computational approaches based on density functional theory (DFT) combined with polarizable continuum model (PCM) of solvation have been used to probe the likelihood of complexation in water between oxo-vanadium(IV) and various medicinal cysteamine-based ligands. The experimental electronic spectra of a complex formed by oxo-vanadium(IV) and penicillamine in water agree well with the theoretical spectra based on the time-dependent density functional theory (TD-DFT) calculations. Among all density functionals adopted, CAM-B3LYP outperforms the others in predicting both structural and spectroscopic properties of oxo-transition metal complexes of cysteamine-based ligands. A variety of chelation behaviors have been found for the ligands tested, depending on the choice of substituent added to the cysteamine backbone. Solvation has a great impact on the thermodynamic driving force for cysteine and its derivatives to undergo complexation. In all cases, the thiolate sulfur atom forms stronger coordination bond than either the amine nitrogen or carboxylate oxygen atoms. Based on the thermodynamic and nucleophilicity index calculations, penicillamine has the highest potential to form complex with oxo-vanadium(IV). [ABSTRACT FROM AUTHOR]

Highlights • Pb retards oxygen into the nickel-based alloy passive film in pure water at 270 ° C. • Pb facilitates the dehydration of Cr(OH) 3 but hinders the dehydration of Ni(OH) 2. • Pb causes a remarkable drop in localized electrical resistivity of passive film. Abstract The degradation mechanism of trace Pb on nickel-based alloy passive film in pure water at 270 ° C is researched by surface analysis techniques and calculations. Experimental results show that Pb reduces the oxygen content and alters the composition of the passive film, resulting in the remarkable drop in its localized electrical resistivity. Density functional theory (DFT) and thermodynamic calculation reveal that the presence of Pb has two effect on the formation of passive film. One is to retard the outward diffusion of oxygen vacancies in the oxide layer, and the other is to affect the dehydration of Cr(OH) 3 and Ni(OH) 2. [ABSTRACT FROM AUTHOR]

The physical behavior of perovskites ATiO 3 (A=Pb, Sn) has been explored by using density functional theory based full-potential linearized-augmented-plane-wave plus local-orbital (FP-LAPW+lo) method. The lattice parameters calculated from the optimized structures by using Murnaghan equation of state and Chapin's method have been found in good agreement with the available literature that ensures the reliability of the adopted methodology. Moreover, the optoelectronic and thermoelectric properties have been elaborated by using modified Becke-Johnson exchange potential. The optical behavior has been explored in terms the dielectric constants, refractive indices, absorption spectra and optical loss factors. The absorption spectra of these materials reveal a large absorption in the visible and low ultraviolet part of incident light. The thermoelectric properties of ATiO 3 are explained in terms of electrical conductivities, thermal conductivities, power factors, and the specific heat capacities. The ATiO 3 family of pervoskites has been found to exhibit the bandgaps falling in the visible region of solar spectrum and show high values of thermal efficiency that make them potential multifunctional candidates for optoelectronic and energy harvesting applications. [ABSTRACT FROM AUTHOR]

From the large variety of C 20 C 720 fullerenes, the energetically most stable isomers were chosen and studied within the PBE/3ζ quantum-chemical approximation. A phenomenological model of the dependence of the standard enthalpy of formation and entropy of the selected isomers on the number of the carbon atoms is developed. From the analysis of the constants of the phenomenological model, it follows that the C 60 , C 70 , C 180 , and C 1500 molecules hold a prominent position among the hypothetical and/or experimentally discovered fullerenes. For the selected energy-stable isomers, the values of the singlet-triplet splitting were calculated. The ground state of the C 260 C 3 , C 320 D 3d and C 500 D 3d molecules were found to be of triplet multiplicity that may indicate their low kinetic stability and/or possibility of existence in the derivatized forms. In view of the lack of relevant experimental thermodynamic data on fullerenes, the obtained in this work approximation dependences, expressed in a simple analytical form, may provide useful tool for fast assessing the energetic characteristics of fullerenes, as well as for prediction of those undiscovered yet. [ABSTRACT FROM AUTHOR]

We assess the feasibility of efficiently calculating accurate thermodynamic properties of (SiO2)n.(H2O)m nanoclusters, using classical interatomic forcefields (FFs). Specifically, we use a recently parameterized FF for hydroxylated bulk silica systems (FFSiOH) to calculate zero-point energies and thermal contributions to vibrational internal energy and entropy, in order to estimate the free energy correction to the internal electronic energy of these nanoclusters. The performance of FFSiOH is then benchmarked against the results of corresponding calculations using density functional theory (DFT) calculations employing the B3LYP functional. Results are reported first for a set of (SiO2)n.(H2O)m clusters with n = 4, 8 and 16, each possessing three different degrees of hydroxylation (R = m/n): 0.0, 0.25 and 0.5. Secondly, we consider five distinct hydroxylated nanocluster isomers with the same (SiO2)16.(H2O)4 composition. Finally, the free energies for the progressive hydroxylation of three nanoclusters with R = 0-0.5 are also calculated. Our results demonstrate that, in all cases, the use of FFSiOH can provide estimates of thermodynamic properties with an accuracy close to that of DFT calculations, and at a fraction of the computational cost. [ABSTRACT FROM AUTHOR]

The exo,anti/exo,syn-diastereoselectivity of water promoted direct aldol reactions of tropinone and granatanone (pseudopelletierine) is strongly dependent on the amount of water added and aromatic aldehyde used. DFT methods were applied to calculate the free energies of tropinone and granatanone enols, transition states, and isomeric aldol products. A theoretical model was verified by comparison of results from several DFT methods and functionals with experiments. The 6-31g(d)/CPCM method proved most suited to the problem, although all methods tested predicted similar trends. Explicit inclusion of a water molecule bonded to the amino ketones resulted in increased stability of the enol forms. The dependence of the anti/syn-diastereoselectivity on the amount of water used may be rationalized on the basis of change in the polarity of the reaction medium. The predicted stabilities of competing products agreed with experimental results supporting the notion of thermodynamic control. The isomeric products distributions for the aldol reaction of several aromatic aldehydes in solventless (neat) conditions were accurately calculated from free energies of the aldol addition step in the gas phase using B3LYP/6-31g(d) method and in aqueous conditions using the CPCM-B3LYP/6-31g(d) model. Our methodology can be useful for predicting the outcome of this type of aldol reactions. [ABSTRACT FROM AUTHOR]

A density functional theory study was performed on the [3+2] cycloaddition (32CA) reaction of 1 H -phosphorinium-3-olate and 1-methylphosphorinium-3-olate with methyl acrylate. The thermodynamic and kinetic parameters were analysed by considering the regio- and stereoisomeric pathways in gas phase and solvents. The geometries indicate that the transition states are slightly more advanced and asynchronous in ethanol. Electron localisation function topological analysis of the bonding changes along the most favourable reaction pathway associated with the 32CA reaction of 1 H -phosphorinium-3-olate with methyl acrylate indicates that the reaction takes place through a two-stage one-step mechanism. Non-covalent interactions analysis of TS6x-H reveals the existence of weak hydrogen bonding explaining the regioselectivity found in this low-polar zw-type 32CA reaction. On comparing these theoretical findings with the nitrogen analogues of the 32CA reactions, it is found that the regioselectivity is affected and the pathways are kinetically and thermodynamically enhanced. Therefore, a priori , the phosphorus cycloadducts could be synthesised. [ABSTRACT FROM AUTHOR]

• Boron single atom anchoring on defective M 3 C 2 O 2-x are used as promising NRR catalysts. • Five selected B@M 3 C 2 O 2-x (M=V, Cr, Nb, Mo and W) show good catalytic performance. • B@V 3 C 2 O 2-x has better NRR activity than TM-doped MXene reported so far. • (ε d - ε p) can serve as a descriptor for NRR activity. The design of efficient catalysts plays an important role in the development of electrochemical nitrogen reduction reaction (NRR). 2D materials MXene can be used as promising catalyst substrates in NRR due to their superior chemical stability and conductivity. Here, using density functional theory calculations, 9 kinds of single-atom catalysts (SACs) B@M 3 C 2 O 2-x (M = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) were constructed by anchoring electron-deficient non-metal boron atom on M 3 C 2 O 2-x with one terminal-O vacancy. All SACs have good thermodynamic and electrochemical stability. The strong acceptor-donor interaction between B atom and N 2 molecule leads to the activation of N 2 , thus promoting NRR. We adopted the screening strategies, including comparing the free energy of N 2 adsorption, the free energy changes for the first and last electrochemical steps of NRR, and the selectivity of hydrogen evolution reaction (HER). Finally, five candidate catalysts (B@V 3 C 2 O 2-x , B@Cr 3 C 2 O 2-x , B@Nb 3 C 2 O 2-x , B@Mo 3 C 2 O 2-x and B@W 3 C 2 O 2-x) were screened out. Starting from the end-on adsorption mode of N 2 , NRR proceeds through a mixed mechanism on each SAC. Our results show that these five SACs have excellent catalytic performance with the limiting potentials ranging from -0.32 to -0.48 V, which may be promising NRR electrocatalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

Using density functional theory, the mechanism of adsorption of 2-chlorophenol from water in the presence of γ-Fe2O3 nanoparticles was investigated. Fe2O3 nanoparticles were modelled using Fe6(OH)18(H2O)6 ring clusters. 2-chlorophenol can coordinate to the γ-Fe2O3 nanoparticles via its own OH or Cl groups. The process produces two intermediates which will be converted into final products through two pathways (Cl pathway and OH pathway). The activation energy and activation Gibbs free energy of the two pathways have been calculated and compared with each other. It was found that the OH pathway is under thermodynamic control and the C1 pathway is under kinetic control. All of the calculations were performed using a hybrid density functional method (B3LYP) in the solution phase (PCM model). [ABSTRACT FROM AUTHOR]