Topology of electrostatic potential and electron density reveals a covalent to non-covalent carbon-carbon bond continuum

The covalent and non-covalent nature of carbon-carbon (CC) interactions in a wide range of molecular systems can be characterized using various methods, including the analysis of molecular electrostatic potential (MESP), represented as V(r), and the molecular electron density (MED), represented as ρ(r). These techniques provide valuable insights into the bonding between carbon atoms in different molecular environments. By uncovering a fundamental exponential relationship between the distance of the CC bond and the highest eigenvalue (λv1) of V(r) at the bond critical point (BCP), this study establishes the continuum model for all types of CC interactions, including transition states. The continuum model is further delineated into three distinct regions, namely covalent, borderline cases, and non-covalent, based on the gradient, , with the bond distance of the CC interaction. For covalent interactions, this parameter exhibits a more negative value than -5.0 a.u. Å-1, while for non-covalent interactions, it is less negative than -1.0 a.u. Å-1. Borderline cases, which encompass transition state structures, fall within the range of -1.0 to -5.0 a.u. Å-1. Furthermore, this study expands upon Popelier's analysis of the Laplacian of the MED, denoted as ∇2ρ, to encompass the entire spectrum of covalent, non-covalent, and borderline cases of CC interactions. Therefore, the present study presents compelling evidence supporting the concept of a continuum model for CC bonds in chemistry. Additionally, this continuum model is further explored within the context of C-N, C-O, C-S, N-N, O-O, and S-S interactions, albeit with a limited dataset.

Double-Regiodetermining-Stages Mechanistic Model Explaining the Regioselectivity of Pd-Catalyzed Hydroaminocarbonylation of Alkenes with Carbon Monoxide and Ammonium Chloride

Pd-catalyzed hydroaminocarbonylation (HAC) of alkenes with CO and NH₄Cl enables atom-economic and regiodivergent synthesis of primary amides, but the origin of regioselectivity was incorrectly interpreted in previous computational studies. A density functional theory study was performed herein to investigate the mechanism. Different from the previous proposals, both alkene insertion and aminolysis were found to be potential regioselectivity-determining stages. In the alkene insertion stage, 2,1-insertion is generally faster than 1,2-insertion irrespective of neutral or cationic pathways for both P(^tBu)₃ and xantphos. Such selectivity results from the unconventional proton-like hydrogen of the Pd-H bond in alkene insertion transition states. For less bulky alkenes, aminolysis with P(^tBu)₃ shows low selectivity, while linear selectivity dominates in this stage with xantphos due to a stronger repulsion between xantphos and branched acyl ligands. It was further revealed that the less-mentioned CO concentration and solvents also influence the regioselectivity by adjusting the relative feasibilities of CO-involved steps and NH₃ release from ammonium chloride, respectively. The presented double-regiodetermining-stages mechanistic model associated with the effects of ligands, CO concentration, and solvents well reproduced the experimental selectivity to prove its validity and illuminated new perspectives for the regioselectivity control of HAC reactions.

Experimental and theoretical studies of sodium acetyldithiocarbamate for the removal of Cu2+ and Ni2+ from aqueous solution

With the continuous worsening of water pollution, the use of various collectors to remove heavy metal ions from aqueous solutions has attracted widespread attention. In this work, an acid-resistant collector, sodium acetyldithiocarbamate (ADTC) that combines acetamide with carbon disulfide was proposed for heavy metal removal. The structure of ADTC was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectrometer (NMR). Flame atomic absorption spectrophotometry (FAAS) was used to detect the concentration of metal ions in the solution before and after the treatment of the chelating agents. The chelation removal efficiency are compared for different chelating agents for Cu²⁺ and Ni²⁺ in acidic aqueous solution with pH = 1-7, and compared to the chelation removal efficiency of sodium diethyldithiocarbamate (DDTC) and sodium ethyl xanthate (SEX) chelating agents. The experimental results suggest the order of the chelating ability is ADTC > DDTC > SEX for Cu²⁺ and Ni²⁺. The chelating ability of ADTC to Ni²⁺ is stronger than that of Cu²⁺. The chelating ability of the collector is greatly affected by the pH value. The ADTC has a good chelating ability in the pH range of 3-7. The molecular orbital distribution, charge and electrostatic potential surfaces in quantum chemistry are used to explore the main active sites of the chelating agent are the S atom. The results of high resolution mass spectrometry showed that the ADTC is coordinated with the positive divalent metal ion in the ratio of 2:1. According to the results, the dithioamino (-NHCSS^-) groups are coordinated with the positive divalent metal ion in a 2:1 ratio. Molecular dynamics simulation is used to explore the adsorption energy and binding strength of the chelating agent on the metal surface.

The mechanism and structure–activity relationship of amide bond formation by silane derivatives: a computational study

The detailed reaction mechanism and structure–activity relationship of substrates in silane reagent-mediated amide bond formation reactions are clarified.

Computational Study of Mechanism and Thermodynamics of Ni/IPr-Catalyzed Amidation of Esters

Nickel catalysis has shown remarkable potential in amide C⁻N bond activation and functionalization. Particularly for the transformation between ester and amide, nickel catalysis has realized both the forward (ester to amide) and reverse (amide to ester) reactions, allowing a powerful approach for the ester and amide synthesis. Based on density functional theory (DFT) calculations, we explored the mechanism and thermodynamics of Ni/IPr-catalyzed amidation with both aromatic and aliphatic esters. The reaction follows the general cross-coupling mechanism, involving sequential oxidative addition, proton transfer, and reductive elimination. The calculations indicated the reversible nature of amidation, which highlights the importance of reaction thermodynamics in related reaction designs. To shed light on the control of thermodynamics, we also investigated the thermodynamic free energy changes of amidation with a series of esters and amides.