Unexpected discovery: "A new 3,3'-bipyrazolo[3,4-b]pyridine scaffold and its comprehensive analysis".

In this study, a novel 3,3'-bipyrazolo [3,4-b]pyridine-type structure was synthesized from 5-acetylamino-3-methyl-1-phenylpyrazole using the Vilsmeier-Haack reaction as a key step. The spectroscopic properties and structural elucidation of the compound were determined with the use of FT-IR, HRMS, 1H NMR, and 13C NMR. Likewise, the theoretical analysis of the IR and NMR spectra allowed peaks to be assigned and a solid correlation was demonstrated between the experimental and theoretical results. Finally, ab initio calculations based on the density functional theory method at the B3LYP/6-311G (d,p) level of theory were used to determine the conformational energy barrier, facilitating the identification of the most probable conformers of the synthesized compound. Overall, our findings contribute to the understanding of bipyrazolo [3,4-b]pyridine derivatives.

Exploring the maximum Fukui function sites with the frontier-controlled soft-soft reactions using 1,3-dipolar cycloaddition reactions of nitrilium betaines.

According to P.K. Chattaraj. J Phys Chem A 2001, 105, 511-513 "the maximum Fukui function site is the best for the frontier-controlled soft-soft reactions whereas for the charge-controlled hard-hard interactions the preferred site is associated with the maximum net charge and not necessarily the minimum Fukui function". Taking into account these outcomes in this research is explored this reactivity scheme using in first case the reaction between fulminic acid with ethylene (reference reaction), after is varying the dipolarophile in the reaction between fulminic acid with acetylene, and finally is varying the dipole in the reaction between formonitrile imine with ethylene. These results allow study parameter such as charge transfer, polarizability, covalent character on bonding, among other; also shown the preference by the sf- / sf+ interactions in the transition state on the sf- / sf- interactions. On the other hand, these results also were justified using net electrophilicity which is defined as the electrophilic power of a system relative to its own nucleophilic power.

Property-oriented basis sets for computation of atomization energies.

The SBO4-DZ(d,p)-3G basis sets introduced in a previous paper have been modified to improve their performance in the calculation of the atomization energies of organic molecules (pure or substituted hydrocarbons). The first step was to explore the possibility of improving those basis sets by adding a second D shell. The scale factor for an additional "D-3G" shell was first studied by minimizing the total energies. In a second step, the scale factor was calculated by optimizing atomization energies directly (instead total energies). This way the results obtained were very similar to those of the cc-pV5Z basis sets. Finally, we optimized simplified box orbital (SBO) basis sets for different methods obtaining optimal SBO basis sets for HF, DFTs, and MP2.

New insights about electronic mechanism of electrocyclic reactions: theoretical study about stereoselectivity in cyclobutenes.

This work presents the study of a series of electrocyclic reactions with the main aim of obtaining new insights into the reaction process along IRCs. The energy variation of the different reaction paths as well as the different transition states have been calculated. These trends are according to the experimental data. The natural bond orbitals have been obtained and the second order perturbational theory analysis has been carried out to determine the main charge transfers due to delocalization. Bond reactivity indexes have been used to describe the reactivity mechanism in a local way. These reactivity indexes are also based on NBOs and this has made it possible to connect the results of the indexes with the previous analysis. To determine quantitatively the bond structure, we used the quantum theory of atoms in molecules and we have hereby completed the information obtained from the NBO analysis. Finally, we used the Hirshfeld population analysis as an approximation to understand how the load density changes in the different reaction pathways, and we have connected these variations with the information obtained from the bond structure. The results has found that the reaction path with the lowest energy barrier Transition State Inward Conrotatory (TSIC) or Transition State Outward Conrotatory (TSOC) is determined by two magnitudes: the charge donations by delocalisation of the substituents (which we obtained from the Second Order Perturbational Theory Analysis of the NBOs) and in the case that these donations were very similar, the non-covalent interactions dominated (which we studied by means of the interaction energies of the Hirshfeld charges). Additionality, the most important factor influencing the lower energy reaction path was the interaction of lone pairs of the substituents with the σ∗(C-C) bond that is broken at the opening of the cycle. The alignment of these lone pairs with the C-C bond favours charge donation between them and, as can be seen in the discussion, this alignment varies depending on whether the structure is TSIC and TSOC.

Bond reactivity indices approach analysis of the [2+2] cycloaddition of jatrophane skeleton diterpenoids from Euphorbia gaditana Coss to tetracyclic gaditanone.

The reaction mechanism of the intramolecular [2 + 2] cycloaddition from a jatrophane precursor to the gaditanane skeleton, an unprecedented 5/6/4/6-fused tetracyclic ring framework recently isolated from Euphorbia spp., was studied using the bond reactivity indices approach. Furthermore, six diterpenoids, including three undescribed jatrophanes isolated from E. gaditana Coss, were described. The structures of these compounds were deduced by a combination of 2D NMR spectroscopy and ECD data analysis.

Discerning the thermal cyclotrimerizations of fluoro- and chloroacetylenes through ELF, NBO descriptors and QTAIM analysis: pseudodiradical character.

In this study the thermal cyclotrimerization reactions of fluoro- and chloroacetylenes involving regioselectively stepwise {2 + 2} and stepwise {4 + 2} cycloadditions were studied using the topological analysis of the electron localization function (ELF), the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. These methodologies have shown that the electronic reorganization in the regioselectively stepwise {2 + 2} and stepwise {4 + 2} cycloadditions may be considered as {2n+2n} and {2π+2n} pseudodiradical process, respectively. Finally, the last phase of this thermal reaction can be understood as an electronic migration process under the pseudodiradical character in the thermal ring-opening reaction, with the subsequent formation of reaction products. In this sense, new insights are reported on the electronic behavior in the bond formation in the thermal cyclotrimerization of fluoroacetylene.

On Electronegativity, Hardness, and Reactivity Descriptors: A New Property-Oriented Basis Set.

In this study, various ways of calculating electronegativity are analyzed after a brief summary of the evolution of this concept. We point out that some commonly used basis sets to calculate this parameter, such as 6-311G(d), provide results with an extraordinarily high margin of error. Therefore, a correction to the 6-311G(d) basis set is proposed that leads to calculations of electronegativity and hardness with a quality similar to those obtained with much broader basis sets, such as Aug-cc-pVQZ and Aug-cc-pV5Z. Since the calculation effort of the proposed basis is small, it can be applied to the accurate calculation of electronegativity and hardness in relatively large systems. It has also been tested in the calculation of reactivity indices and we have obtained results similar to those of the Aug-cc-pV5Z basis set. Finally, we have studied the densities corresponding to the frontier molecular orbitals in a representative sample set of molecules, using both the improved and other standard basis sets, and we have verified that the quality level of the proposed basis set is clearly better than that of standard basis sets with a similar calculation effort.

Software to obtain spatially localized functions from different radial functions.

We have developed an algorithm that enables simplified box orbital functions (SBO) to be obtained with optimized coefficients by fitting them to functions of many types. SBOs are a linear combination of radial functions useful in quantum chemistry calculations which can be spatially restricted (defined in [Formula: see text] interval, and zero for [Formula: see text]). The algorithm proposed makes it possible to obtain the optimal radius [Formula: see text] and the coefficients of the SBOs of any number of terms from the functions to be fitted, but also allows the user to define a particular radius r and calculate the coefficients of the combination of terms of the SBOs. SBOs have proved to be useful in the calculation of molecular properties, and can reduce the complexity of the integral calculations, especially in huge chemical systems such as atomic clusters. These types of functions are also adequate for studying confined systems such as molecules in solution or big chemical systems such as atomic clusters. In addition, while carrying out the examples presented in this study we have tested the suitability of SBO functions to calculate molecular reactivity, showing that the basis functions provide results as good as the basis sets typically used for this kind of calculations.

Correlations between Fukui Indices and Reactivity Descriptors Based on Sanderson's Principle.

A previous study presented a very simple model mainly based on Sanderson's principle for estimating important reactivity descriptors, such as the local hardness and the local electrophilicity. In another study, a new way of calculating the Fukui function was obtained that resulted in a new operative formula for the function. We also obtained the second-order partial derivative of the electron density with regard to the number of electrons. The current study analyzes the relationships between the two models and justifies the origin of these relationships.

New advances in conceptual-DFT: an alternative way to calculate the Fukui function and dual descriptor.

An alternative way of calculating the Fukui function and the partial derivative of second order of the electronic density with respect to the number of electrons N is presented, the new formulas agree with the usual ones but only in cases without degeneracy. The new operative formulas are more general than the previous ones and are the right ones for those problematic cases where one or both of the frontier molecular orbitals are degenerate. Finally, we present a new way of applying the finite difference approximation that leads to more realistic results than the usual formulas. Graphical abstract A new way of calculating the Fukui function is presented that results in a new operative formula of the function. It has also been obtained the partial derivative of second order of the electronic density with respect to the number of electrons N, and it agree with the usual formula of the dual descriptor function but only in cases without degeneration.

Introducing a new bond reactivity index: Philicities for natural bond orbitals.

In the present work, a new methodology defined for obtaining reactivity indices (philicities) is proposed. This is based on reactivity functions such as the Fukui function or the dual descriptor, and makes it possible to project the information from reactivity functions onto molecular orbitals, instead of onto the atoms of the molecule (atomic reactivity indices). The methodology focuses on the molecules' natural bond orbitals (bond reactivity indices) because these orbitals have the advantage of being localized, allowing the reaction site of an electrophile or nucleophile to be determined within a very precise molecular region. This methodology provides a "philicity" index for every NBO, and a representative set of molecules has been used to test the new definition. A new methodology has also been developed to compare the "finite difference" and the "frontier molecular orbital" approximations. To facilitate their use, the proposed methodology as well as the possibility of calculating the new indices have been implemented in a new version of UCA-FUKUI software. In addition, condensation schemes based on atomic populations of the "atoms in molecules" theory, the Hirshfeld population analysis, the approximation of Mulliken (with a minimal basis set) and electrostatic potential-derived charges have also been implemented, including the calculation of "bond reactivity indices" defined in previous studies. Graphical abstract A new methodology defined for obtaining bond reactivity indices (philicities) is proposed and makes it possible to project the information from reactivity functions onto molecular orbitals. The proposed methodology as well as the possibility of calculating the new indices have been implemented in a new version of UCA-FUKUI software. In addition, this version can use new atomic condensation schemes and new "utilities" have also been included in this second version.

Introducing new reactivity descriptors: "Bond reactivity indices." Comparison of the new definitions and atomic reactivity indices.

A new methodology to obtain reactivity indices has been defined. This is based on reactivity functions such as the Fukui function or the dual descriptor and makes it possible to project the information of reactivity functions over molecular orbitals instead of the atoms of the molecule (atomic reactivity indices). The methodology focuses on the molecule's natural bond orbitals (bond reactivity indices) because these orbitals (with physical meaning) have the advantage of being very localized, allowing the reaction site of an electrophile or nucleophile to be determined within a very precise molecular region. This methodology gives a reactivity index for every Natural Bond Orbital (NBO), and we have verified that they have equivalent information to the reactivity functions. A representative set of molecules has been used to test the new definitions. Also, the bond reactivity index has been related with the atomic reactivity one, and complementary information has been obtained from the comparison. Finally, a new atomic reactivity index has been defined and compared with previous definitions.

Reactivity indices for natural bond orbitals: a new methodology.

A new reactivity index has been defined; this parameter is focused on a molecule's natural bond orbitals (NBOs) and derives in a natural way from Fukui functions. NBOs have the advantage of being very localized, allowing the reaction site of an electrophile or nucleophile to be determined within a very precise molecular region. Finally, the indices for a representative set of organic molecules were calculated and their usefulness tested on some protonation reactions.

Introducing "UCA-FUKUI" software: reactivity-index calculations.

A new software (UCA-FUKUI) has been developed to facilitate the theoretical study of chemical reactivity. This program can calculate global parameters like hardness, softness, philicities, and Fukui condensed functions, and also local parameters from the condensed functions. To facilitate access to the program we have developed a very easy-to-use interface. We have tested the performance of the software by calculating the global and local reactivity indexes of a group of representative molecules. Finite difference and frontier molecular orbital methods were compared and their correlation tested. Finally, we have extended the analysis to a set of ligands of importance in coordination chemistry, and the results are compared with the exact calculation. As a general trend, our study shows the existence of a high correlation between global parameters, but a weaker correlation between local parameters.

Experimental and theoretical study of the electronic properties of Cu-doped anatase TiO2.

A good correlation was obtained between the electronic properties of Cu-doped anatase TiO2 by virtue of both physical chemistry characterization and theoretical calculations. Pure and Cu-doped TiO2 were synthesized. The composition, structural and electronic properties, and the band gap energy were obtained using several techniques. The method of synthesis used produces Cu-doped anatase TiO2, and XRD, XPS and Raman spectroscopy indicate that Cu atoms are incorporated in the structure by substitution of Ti atoms, generating a distortion of the structure and oxygen vacancies. In turn, the band gap energy of the synthesized samples decrease drastically with the Cu doping. Moreover, periodic density functional theory (DFT-periodic) calculations were carried out both to model the experimentally observed doped structures and to understand theoretically the experimental structures obtained, the formation of oxygen vacancies and the values of the band gap energy. From the analysis of density of states (DOS), projected density of states (PDOS) and the electron localization function (ELF) a decrease in the band gap is predicted upon increasing the Cu doping. Thus, the inclusion of Cu in the anatase structure implies a covalent character in the Cu-O interaction, which involves the appearance of new states in the valence band maximum with a narrowing in the band gap.