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Grid is a free and open-source Python library for constructing numerical grids to integrate, interpolate, and differentiate functions (e.g., molecular properties), with a strong emphasis on facilitating these operations in computational chemistry and conceptual density functional theory. Although designed, maintained, and released as a stand-alone Python library, Grid was originally developed for molecular integration, interpolation, and solving the Poisson equation in the HORTON and ChemTools packages. Grid is designed to be easy to use, extend, and maintain; this is why we use Python and adopt many principles of modern software development, including comprehensive documentation, extensive testing, continuous integration/delivery protocols, and package management. We leverage popular scientific packages, such as NumPy and SciPy, to ensure high efficiency and optimized performance in grid development. This article is the official release note of the Grid library showcasing its unique functionality and scope. [ABSTRACT FROM AUTHOR]

The hard/soft acid/base (HSAB) principle is a cornerstone in our understanding of chemical reactivity preferences. Motivated by the success of the original ("global") version of this rule, a "local" counterpart was readily proposed to account for regioselectivity preferences, in particular, in ambident reactions. However, ample experimental evidence indicates that the local HSAB principle often fails to provide meaningful predictions. Here we examine the assumptions behind the standard proof of the local HSAB rule, showing that it is based on a flawed premise. By solving this issue, we show that it is critical to consider not only the charge transferred between the different reacting centers but also the charge reorganization within the non-reacting parts of the molecule. We propose different reorganization models and derive the corresponding regioselectivity rules for each. [ABSTRACT FROM AUTHOR]

Dipolar cycloaddition reactions involving munchnönes and simple dipolarophiles provide a versatile synthetic route toward pyrrole derivatives. However, despite their widespread use, there are still debates regarding the factors governing the regio-selectivity of these reactions. In this contribution, we study the regio-selectivity of 1,3-dipolar cycloadditions of munchnönes and alkenes, and the ability of conceptual density functional theory (c-DFT) descriptors to correctly study these processes. We base our analysis on the variation of different reactivity descriptors along the reaction path, calculated for the whole reacting complex, and for the isolated species, with the strained geometries they present within this supra-molecular aggregate. The study of several global descriptors indicates that the path leading to the preferred product proceeds via an asynchronous mechanism, with the maximum extent of charge transfer occurring after the transition state. This helps to understand why several reactivity principles fail to correctly account for the position of the transition state in this case. This also explains why local c-DFT descriptors fail to predict the observed majoritarian regio-isomer. These results highlight the fundamental role of the distortion effects for determining the extent of charge transfer between the reactants, and thus their impact on the reactivity and regio-selectivity in these reactions. [ABSTRACT FROM AUTHOR]

To assess the title issue, 38 hydrogen transfer barrier heights and 38 non-hydrogen transfer barrier heights/isomerizations extracted from extensive databases have been considered, in addition to 4 2 p-isomerization reactions and 6 others for large organic molecules. All Kohn-Sham DFT calculations have employed the popular M06-2X functional, whereas the correlated molecular orbital (MO)-based ones are from single-reference MP2 and CCSD(T) methods. They have all utilized the same basis sets, with raw MO energies subsequently extrapolated to the complete basis set limit without additional cost. MP2 calculations are found to be as cost-effective as DFT ones and often slightly more, while showing a satisfactory accuracy when compared with the reference data. Although the focus is on barrier heights, the results may bear broader implications, in that one may see successes and difficulties of DFT when compared with traditional MO theories for the same data. [ABSTRACT FROM AUTHOR]

The retro-cycloaddition thermal reaction of isoxazolino[4,5:1,2][60]fullerenes to pristine fullerene seems to be guided by the electronic nature of the substituted nitrile oxide 1,3-dipole in the isoxazoline ring. Trapping experiments proved that the reaction mechanism occurs by thermal removal of the nitrile oxide 1,3-dipole in a process that is favored in the presence of a big excess of a highly efficient dipolarophile such as maleic anhydride. Theoretical gas phase calculations carried out at the B3LYP/6-31G(d) and M06-2X/6-31G(d) levels of theory underpin the experimental findings and predict that compound 1c, bearing the p-(CH3)2N-Ph substituent on the isoxazoline ring and with a remarkable experimental conversion efficiency in just 12 h, showed the lowest activation energy. Solvent calculations have predicted the same behavior in gas phase. Different approaches such as electrostatic natural population analysis and Houk's distortion/interaction model have been applied to understand how the electronic nature of these substituents affects the retro-cycloaddition reaction process. Analysis of the values of the condensed Fukui functions and dual descriptor shed light on the mechanism of the retro-cycloaddition reaction. [ABSTRACT FROM AUTHOR]

Using the maximum hardness principle, we show that the oxidation potential of a molecule increases as its electronegativity increases and also increases as its electronegativity in its oxidized state increases. This insight can be used to construct a linear free energy relation for the oxidation potential, which we train on a set of 31 organic redox couples and test on a set of 10 different redox reactions. Better results are obtained when the electronegativity of the oxidized/reduced reagents are adjusted to account for the reagents' interaction with their chemical environment. [ABSTRACT FROM AUTHOR]