Abstract: The dependences of differential spectral parameters (Δδi H) in spectra NMR 1H of monosubstituted benzenes C6H5X on substituent constants (σ) were investigated. The best correlation was founded for set of para-Brown's constants (σ+).

Abstract: The reaction pathways for the addition of OH- ion to cyclobutane-1,2-dione I are calculated by density functional theory procedures [B3LYP/6-31+G(d,p)]. Initially, I undergoes attack of the nucleophile, in this case OH- ion, at one of the two equivalent carbonyl carbon atoms leading to formation of a tetrahedral intermediate followed by rearrangement reactions. Density functional theory method (B3LYP) with basis set (6-31+G (d,p) are used to investigate the addition of OH- (hydrated) to the hydrated species of I. The most likely pathway consists in a ring contraction of the tetrahedral intermediate, formed from addition of OH– to I, leading to 1-cyclopropan-1-carboxylic acid.

Abstract: The present communication-reports a study on the variation of some structural and electronic properties related with electron conduction for the series of compounds represented by the formula Ph-(C2+nN4-nHn)-Ph, n=0-4. Properties such as planarity, aromaticity, band gap, and adiabatic electron affinity were analyzed from a theoretical perspective as a function of the number of nitrogen atoms in the molecular structure.

Abstract: Different partial charge distribution methodologies (Mulliken, Löwdin, Hirshfeld, Natural Population Analysis, Merz–Kollman Electrostatic Potential) were used for charge determination in manganese and zinc Schiff base complexes that are isostructural analogs. Chemical reliable clusters were chosen on the ground of experimental X-ray data. Packing effect on charges was found to be negligible. All calculation employed non hybrid ab-initio GGA PBE density functional method with conjunction of different basis sets to show small influence of basis set incompleteness. On the ground of chemical bonding theory Hishfeld partial charge definition was found to be most reliable in different situation – different spin states, H–bonding, molecular crystal and clusters.

Abstract: The reaction of substituted furans a-c and Danishefsky's diene which yield 5-benzofuranol derivatives has been studied using the hardness, the polarizability and the electrophilicity of the corresponding D-A primary adducts as global reactivity indexes. The main objective of this work is to investigate the power of these global indexes in predicting the major regioisomer. It has been demonstrated that both the hardness as well as the electrophilicity power of the adducts are appropriate descriptors for predicting the major product of the reactions at least in the cases study here. The maximum hardness principle and the minimun electropilicity principle are obeyed in these regiospecific Diels–Alder reactions. The stereoselectivity of the D-A reactions has also been studied.

Abstract: not available

Abstract: A comprehensive MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) study of the aromatic character of phospholes, Pn(CH)4-nPH with n = 0-4 was conducted. For this purpose, the structures for these compounds were optimized at both theoretical levels and different magnetic properties (magnetic susceptibility, χ, magnetic susceptibility anisotropy, χanis, and the nucleus-independent chemical shifts, NICS) were evaluated. For comparison, these magnetic properties were also calculated in the optimized structures with planarity constraints. We have also applied the ACID (anisotropy of the current-induced density) method in this analysis. The main conclusions are the aromatic character of these compounds, the relationship between aromaticity and planarity and the importance of other factors in this aromaticity.

Abstract: not available

Abstract: Complexes formed by anions and substituted molecular bowls were studied by means of computational calculations with density functional theory methods. An empirical dispersion term was included to correct the well known flaws of common functionals to describe dispersion interactions. The modified bowls consisted of corannulene molecules substituted with five or ten F, Cl, or CN units, whereas Cl-, Br- and BF4 - where the anions considered. Substitution with F, Cl and CN produces an inversion of the molecular electrostatic potential of the bowls, which become positive over the two faces of the bowl, therefore interacting favorably with anions. Three different structures were found for each of the complexes, corresponding to one arrangement with the anion interacting with the concave side of the bowl and two different arrangements with the anions interacting with the convex side of the bowl. The strength of the interaction roughly follows the values of molecular electrostatic potential, being more stable as more positive is the potential. However, the role of dispersion arises as essential for having a correct order of stabilities. In fact, when dispersion is included, most complexes are more stable by the concave face, where the closer proximity of the atoms allows for a larger dispersion effect. Also, it is dispersion which makes the complexes formed with a larger anion as BF4 - as stable as those formed with Cl- or Br-. The results suggest the possibility of employing these substituted molecular bowls as receptors for anions with a preferential concave complexation, specially for structured anions where dispersion effects will be larger.

Abstract: Optimized geometry and the corresponding electronic structure and thermodynamic properties of cyclopropylmethoxychlorocarbene (cpmcc), 3-cyclopropylmethoxy-3- chlorodiazirine and their -N2 and –CO elimination and consequent rearrangement products, cyclopropylmethoxyfluorocarbene (cpmfc), 3-cyclopropylmethoxy-3-fluorodiazirine and its transition state and cyclopropylmethoxyhydrocarbene (cpmhc), 3-cyclopropylmethoxy-3- hydrodiazirine and its transition state have been calculated using ab initio methods DFTB3LYP with 6-311++G** basis set. The effect of substitutions was investigated on thermodynamic properties of conversion of 3-cyclopropylmethoxy-3-chloro (flouro or hydro) diazirine to different products. Also, nuclear magnetic resonance chemical shifts have been calculated for reactant, transition state and product with various substitutions.

Abstract: Thiiranium heterocycles play an important role in a biocatalytic processes of cells. Usually formation of thiiranium ions are known to proceed by the electrophilic additions of sulfenylhalides to a substituted olefins. We focused attention on the electrophilic addition reaction of methylsulfenyl chloride to the propene. In our work this reaction have been modeled using Ab-initio methods at the MP2/6-31+G(d,f) level of theory to look into the mechanism of the reaction and to explain how the regioselectivity of the reaction is controlled. Calculations of the intrinsic reaction coordinate on the minimum energy pathway revealed the stepwise mechanism for the addition reaction.

Abstract: There are many enantioselective reactions of organolithium to imines described in a very different conditions. In this work, we constructed from experimental outcomes large Complex Network, which may be used to perform datamining and quantitatively describe changes in reaction variables that determine the enantiomeric excess and configuration of the stereogenic centre formed in product.

Abstract: Optimized geometry and the corresponding electronic structure, vibrational frequencies and thermodynamic properties of cyclopropylmethoxychlorocarbene (cpmcc), 3- cyclopropylmethoxy-3-chlorodiazirine have been calculated using ab initio methods DFTB3LYP with 6-311++G** basis set. Results show that cpmcc is transition state with a first order TS saddle point. The displacement matrix of the negative mode of vibration of the TS specie shows that the reaction path follows in the direction of the elimination of the CO group which is consistent with the mechanism proposed upon experimental data. Calculations were also carried out for reactants and products at the same levels of theory. Nuclear quadrupole coupling constants (NQCC), χ, and asymmetry parameter, η, of the 2H, 35Cl nuclei have been calculated for reactants, transition states and products.

Abstract: Classification algorithms are proposed based on information entropy. It is studied the molecular classification of anti-human immunodeficiency virus thiocarbamates. The 62 thiocarbamates (TCs) are classified by their structural chemical properties. Many classification algorithms are based on information entropy. An excessive number of results appear compatible with the data and suffer combinatorial explosion. However, after the equipartition conjecture one has a selection criterion. According to this conjecture, the best configuration of a flowsheet is that in which entropy production is most uniformly distributed. The structural elements of an inhibitor can be ranked according to their inhibitory activity in the order: B1/2 > R > R1 > R2 substitution. In TC 17, B1/2 = B1, R = 4-CH3 and R1 = R2 = H; its associated vector is unary. The TC 17 is selected as a reference. In some TCs B1/2 = B1, in some others B1/2 = B2. The analysis is in qualitative agreement with other classification taken as good based on k-means clustering. Program MolClas is a simple, reliable, efficient and fast procedure for molecular classification, based on the equipartition conjecture of entropy production. The structural elements allow the periodic classification of the TCs. A validation is performed with an external property, cytoprotection activity, not used in the development of the table.

Abstract: not available

Abstract: Quantitative structure-affinity relationships were applied to a series of 27 disperse dyes by partial least squares (PLS) analysis and compared to previously published MLR (multiple linear regression), MTD (minimum steric difference) and CoMFA (comparative molecular field analysis) results. Calculated 0D, 1D and 2D structural dye features were correlated to their affinity for cellulose by PLS. A robust model (R2X(cum) = 0.617, R2Y(cum) = 0.959, Q2(cum) = 0.953) with predictive power was obtained from these correlations. Better statistical results were achieved in the PLS model, in comparison to the previous MLR, MTD and CoMFA results, but the three-dimensional models obtained by CoMFA gave more information on the dye-cellulose specific interactions.

Abstract: test abstract

Abstract: In this work, we have studied from a theoretical perspective the electronic properties such as HOMO → LUMO excitation energy, ionization potential and reorganization energy of oligotiophenes and their alkyl and alcoxy derivatives. The effect of charge injection was also studied. The oligomeric approximation was employed in order to calculate the band gap and ionization potential of an ideal polymeric chain for each one of the selected systems. The variation of reorganization energy on the backbone length was also analyzed.

Abstract: The non-stochastic and stochastic atom-based quadratic indices are applied to develop quantitative structure-activity relationship (QSAR) models for the prediction of aquatic toxicity. The used dataset, consisting of 392 benzene derivatives for which toxicity data to the ciliate Tetrahymena pyriformis were available, is divided into training and test sets. The obtained multiple linear regression models are statistically significant (R2 = 0.787 and s = 0.347, R2 = 0.806 and s = 0.329, for non-stochastic and stochastic quadratic indices, respectively) and show rather good stability in a cross-validation experiment (q2 = 0.769 and scv = 0.357, q2 = 0.791 and scv = 0.337, correspondingly). In addition, a validation through an external test set is performed, which yields significant values of R2 pred of 0.745 and 0.742. The comparison with other approaches exposes a good behavior of our method of predicting the aquatic toxicity of benzenes. The obtained results suggest that, the non-stochastic and stochastic quadratic indices seem to provide an interesting alternative to costly and timeconsuming experiments for determining toxicity.

Abstract: The mechanism of ketonization of acetic acid over SiO₂ was investigated by semiempirical quantum chemical AM1 method using the cluster approach. It has been found that the adjacent acid-base pair of the catalytic sites provokes dissociative adsorption of the acetic acid molecules resulting in the formation of surface carboxylate species. The adsorption process proceeds spontaneously. After blocking the acid-base pairs of catalyst, the new portions of acetic acid molecules interact with active species in the gas phase, converting into acyl cations. The adsorbed carboxylate species is attacked from the methyl group side by the acyl cation resulting in the formation of an acetone molecule and CO₂ by bimolecular electrophilic substitution reaction.

Abstract: The concept of bond-based quadratic indices is generalized to codify chemical structure information for chiral drugs, making use of a trigonometric 3D-chirality correction factor. In order to evaluate the effectiveness of this novel approach in drug design, we have modeled several well-known data sets. In particularly, Cramer's steroid data set has become a benchmark for the assessment of novel QSAR methods. This data set has been used by several researchers using 3D-QSAR approaches. Therefore, it is selected by us for the shake of comparability. In addition, to evaluate the effectiveness of this novel approach in drug design, we model the angiotensin-converting enzyme inhibitory activity of perindoprilate's σ-stereoisomers combinatorial library, as well as codify information related to a pharmacological property, highly dependent on the molecular symmetry, of a set of seven pairs of chiral N-alkylated 3-(3-hydroxyphenyl)-piperidines, which bind σ-receptors. The validation of this method is achieved by comparison with earlier publications applied to the same data sets. The non-stochastic and stochastic bond-based 3D-chiral quadratic indices appear to provide a rather interesting alternative to other more common 3D-QSAR descriptors.