Face-selectivity in [4+2]-cycloadditions to novel polycyclic benzoquinones. Remarkable stereodirecting effects of a remote cyclopropane ring and an olefinic bond

π-Face selectivity in Diels-Alder reactions between specially crafted bicyclo[2.2.2]octane-fused benzoquinones, where the dienophilic moiety is imbedded in an isosteric environment, can be modulated by a remote olefinic bond and a cyclopropane ring. Quantum mechanical calculations while reproducing the observed diastereoselectivities at the TS level indicate the involvement of ground state orbital effects

The Role of Homoaromaticity in the Tropylium-Catalyzed Carboxylic Acid O-H Insertion with Diazoesters

The tropylium catalyzed carboxylic acid O-H insertion with diazoesters providing α-hydroxy esters was reported recently through an activated carbene as the key intermediate. We report a revised mechanism involving a unique homoaromatic intermediate with the tropylium ion and the diazoester based on the DFT calculations. Our computational model provides a clear insight into the binding of the tropylium ion with the diazoester providing the homoaromatic intermediate. The reaction profiles of four different pathways were compared. The energies of the intermediates and the transition states are reported at B97-D3(SMD)/def2TZVP//B97-D3/def2TZVP (in dichloromethane). The energy profiles were compared across a few computational methods to study the sensitivity of our model across methods

Insights into the active catalyst formation in palladium catalyzed coupling reaction from di-nuclear palladium acetate: A DFT study

We explored the formation of active palladium catalyst species by degradation of Pd-acetate dimer with the addition of phosphine ligands (PH3 and PPh3 ) with an automated reaction search employing Density Functional Theory calculations followed by kinetic studies with stochastic simulation analysis. Our reaction search starting from dimeric form, considered a resting state of the catalyst, produced similar monomeric species by sequential ligand addition as found in the experimental investigation of the active catalytic species in Heck reactions. We analyzed the bonding in the Pd-acetate dimer and the role of Pd in the stability of the dimeric species. We implemented the Gillespie Stochastic Simulation Algorithm and applied it to the degradation reaction path. This algorithm can give more insights into multi-channel reaction paths. The energetics of the degradation path is reasonably achievable in the experimental reaction conditions that make dimeric species a potential catalytic precursor in the Pd-acetate catalyzed coupling reactions

Potential Prebiotic Pathways in Titan’s Atmosphere: A Computational Exploration of HCN and NH3 Reactions

In this study, we explore the potential for prebiotic chemistry in Titan’s atmosphere through computational modeling of reactions involving hydrogen cyanide (HCN), hydrogen isocyanide (HNC), and ammonia (NH3). Our automated reaction search identifies several key intermediates, including formamidine (A), hydrazone (B), and methanediimine (C), which serve as precursors for a variety of complex organic com- pounds. Among the products, methanamine (P5) and guanidine (P22) are highlighted for their relevance to early biological activity. The calculated low activation barriers and exothermic nature of several reactions suggest the viability of these pathways in Titan’s cold environment. Notably, the formation of molecules such as a triazole derivative (P18) and N-cyanoimidoformamide (P20), linked to biomarker cyanamide, underscores the potential for synthesizing biologically significant molecules. We pro- vide theoretical roto-vibrational spectral parameters to assist in the experimental de- tection of these species, offering insights into the molecular complexity achievable in Titan’s atmosphere and contributing to our understanding of prebiotic chemistry in extraterrestrial environments

Computational Study of Tandem C-C Coupling and C-H Activation Reaction of a Flexible Substrate

We carried out an extensive density functional theory calculations on the Pd catalyzed intramolecular Heck reaction followed by C-H activation of a flexible substrate like Stilbene system<br /

Control of stability through overlap matching: closo-carborynes and closo-silaborynes

The matching of ring and cap orbitals for overlap is used to arrive at the best carborynes among the many possibilities. Accordingly, 1,2-carboranes, 1,2-silaboranes (C2BnHn+2, and Si2BnHn+2, n = 4, 5, 8, and 10), and their dehydrogeno derivatives were studied with use of the Density Functional Theory (B3LYP/6-311+G&#8727;). The dehydrogenation of 2,3-C2B5H7 (6a) to 2,3-C2B5H5 (13a) is estimated to be even less endothermic than those of benzene and 1,2- C2B10H12 (1a) to benzyne and 1,2-C2B10H10 (8a) by more than 21 kcal/mol. This is due to the extra stabilization gained through better overlap of the C2B3H3 ring with the 2 BH caps. The relatively larger size of the Si atom leads to overlap requirements in silaboranes that are different from those in carboranes. The lower Si-Si single bond energy and the preference of Si for lower coordination result in unusual structures in dehydrogenosilaboranes. One of the Si atoms moves away from the surface in Si2B10H10 (15), Si2B8H8 (16, 17, and 18), and 1,2-Si2B5H5 (19). One Si atom forms a bridge to a trigonal surface in 2,3-Si2B5H5 (20) and 1,2-Si2B4H4 (21). Estimates of three-dimensional aromaticity with NICS calculations show that the exohedral double bond does not influence three-dimensional aromaticity

Does the Mechanism of the Garratt–Braverman Cyclization Differ with Substrates? A Computational Study on Bispropargyl Sulfones, Sulfides, Ethers, Amines, and Methanes

We studied the variation in mechanism among different bispropargyl substratessulfone, sulfide, ether, amine, and methanetoward Garratt–Braverman (GB) cyclization using density functional theory calculations. Isomerization and cycloaddition are the key steps in the GB cyclization. To compare the reactivity among the various substrates, we computed the free energy of activation (Δ<i>G</i>^⧧) for the cycloaddition and the cyclization steps, whereas we used the theoretically computed p<i>K</i>_a values for the isomerization steps. Our results suggest that the sulfones undergo a relatively fast isomerization followed by slower cyclization, while the ethers undergo a slow isomerization followed by easy cyclization. The methanes and amines are similar to the ethers, and the sulfides showed intermediate behavior. We extended our study to unsymmetrical substrates and compare the results with experiments that suggest the isomerization to be the rate-limiting step for bispropargyl ethers, while cyclization through a diradical intermediate is crucial to the rate for the bispropargyl sulfones. On the basis of these findings, we made predictions on the selectivity of unsymmetrical bispropargyl sulfones, amines, methanes, and sulfides. This is the first detailed mechanistic study on the GB cyclization of bispropargyl substrates other than sulfones

HCN Dimers to HCN Tetramers: Computational Exploration of Binary Reactions

This study explores the self and cross-dimerization of HCN and HNC dimers, key elements in prebiotic chemistry, to explore potential phenomena crucial to the early stages of life on Earth, Titan, and other extraterrestrial environments. We utilise computational analysis to reveal various reaction products, predominantly featuring imine, nitrile, amine, and iminoamine functional groups, along with N-heterocycles like aziridines, azetenes, and triazole. Transition state search methods illuminate the mechanistic details of these reactions. Notably, we identify biomarkers such as a func- tional isomer of DAMN (D95) and imidazole derivatives (D45, D76, D79), which are potential precursors to nucleobases such as adenine, and polyimines that may serve as precursors to DNA and RNA helical structures. This study enhances our under- standing of the complex chemical pathways that may have contributed to the genesis of life’s foundational molecules in various cosmic settings

Effect of metal complexation on ring opening of bowl-shaped hydrocarbons: theoretical study

Density functional theory study on benzenoid and tris-acetylenic structure of fullerene and its fragments shows that tris-acetylenic model structures lead to benzenoid model structure due to the proximity of p-orbitals in the former. The tris-acetylenic model structures are stabilized on metal complexation in comparison to the parent benzene-acetylene equilibrium. In going from Cr to Co, the acetylenic metal complex becomes more stabilized than the benzene-metal complex. The curved surface of the tris-acetylenic fullerene fragments causes one set of π-orbital of the tris-acetylenic groups to rehybridize so as to bend more toward the metal fragments than found in the parent acetylene complexes. This leads to the increased overlap between metal fragments and tris-acetylenic model structures. We also studied the benzenoid and tris-acetylenic model complexes of C<SUB>12</SUB>H<SUB>6</SUB> and C<SUB>12</SUB>H<SUB>12</SUB> where five-membered rings are replaced with more strained four-membered rings