On the initial treatment of kinetic data

The kinetic methods usually employed to determine reaction orders involve some sort of mathematical approximation and provide values approximate and very often discrepant. Three methods are reported to determine accurate reaction orders without introducing approximations.

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Altered Volcanic Tuffs from Los Frailes Caldera. A Study of Their Pozzolanic Properties

This work presents the results of the study of the physical, chemical, mineralogical and pozzolanic properties of the altered volcanic tuffs (AVT) that lie in the Los Frailes caldera, south of the Iberian Peninsula, and demonstrates their qualities as pozzolans for the manufacturing of mortars and pozzolanic cements of high mechanical strength. The main objective of this research is to show to what extent the AVTs can replace portland cement (PC) in mortars, with standardised proportions of 75:25% and 70:30% (PC-AVT). To achieve these objectives, three AVT samples were studied by a petrographic analysis of thin section (PATS), DRX, FRX and MEB. The pozzolanic properties were determined by three methods: electrical conductivity (ECT), chemical pozzolanicity tests (CPT) at 8 and 15 days and mechanical strength tests (MS) of the specimens at 2, 7, 28 and 90 days. Studies of a PATS, DRX, FRX and MEB showed that the AVT samples’ constitutions are complex where smectite (montmorillonite), mordenite, quartz, halloysite, illite, kaolinite, volcanic glass and lithic fragments coexist. The results of the ECT and CPT tests confirmed the pozzolanic properties of the samples analysed and proved an increase in mechanical strength from 2 to 90 days of testing.     

Effect of concentration, particle size and the presence of protective coatings in DRIFT spectra of building materials

This paper discusses the effect of particle size (from under 45 to 425 μm), sample concentration (5 and 50% dilution in KBr) and the presence/absence of anti-graffiti coatings on the quality of diffuse reflectance spectra, specifically the spectra for limestone, granite and brick. In limestone, sample dilution was found to affect spectral resolution significantly, whereas the increase in particle size leads to a slight decrease in signal intensity. The presence of anti-graffiti protection was the factor that disturbed spectral quality most visibly, except in very dilute (5%) samples with a very fine particle size (under 45 μm). In more heterogeneous materials such as brick and granite, particle size proved to have a greater impact than dilution, while the presence of protective treatment was again the parameter with the greatest effect on quality and consequently signal reproducibility. This effect was slighter in very dilute samples with a small particle size.     

Intramolecular Diels-Alder reaction of 1-aminoisobenzofurans: Application to the synthesis of benzo[c]phenanthridines

Intramolecular Diels-Alder reactions of 1-aminoisobenzofurans give benzo[c]phenanthridines. The reactive intermediates are generated from o-(diazomethyl)benzamides.     

Simple one-step ultrasonic synthesis of anatase titania/polypyrrole nanocomposites

In this work, hybrid nanocomposites based on anatase titania:polypyrrole (TiO₂:PPy) were directly obtained from a simple, one-step, ultrasonic (UT)-assisted synthesis. The properties of these crystalline nanocomposites were compared with those of others fabricated using cold (Cold)-assisted synthesis without any UT assistance, which required a hydrothermal treatment (HT) to yield crystalline anatase titania in the nanocomposite (TiO₂:PPy) at low temperature (130 °C) and in a short time (3 h). The SEM results demonstrated that the UT-assisted synthesis is a feasible method to obtain anatase TiO₂:PPy nanocomposites with controlled morphology using low energy. The Fourier transform infrared (FT-IR) bands of the crystalline nanocomposites exhibited a shift with respect to neat components, which was attributed to the strong interaction between the secondary amine groups (N–H) of PPy and the oxygen from TiO₂. The acceptable absorption in the visible region (λ_max = 670 nm) indicates that these nanocomposites are good candidates for harvesting energy in solar cells. Devices based on these nanocomposites were built to evaluate their electrical properties. An increase in the photocurrent was observed for the devices prepared with the nanocomposites from the UT-assisted synthesis.     

DFT study on the cycloreversion of thietane radical cations

The molecular mechanism of the cycloreversion (CR) of thietane radical cations has been analyzed in detail at the UB3LYP/6-31G* level of theory. Results have shown that the process takes place via a stepwise mechanism leading to alkenes and thiobenzophenone; alternatively, formal [4+2] cycloadducts are obtained. Thus, the CR of radical cations 1a,b(?+) is initiated by C2-C3 bond breaking, giving common intermediates INa,b. At this stage, two reaction pathways are feasible involving ion molecule complexes IMCa,b (i) or radical cations 4a,b(?+) (ii). Calculations support that 1a(?+) follows reaction pathway ii (leading to the formal [4+2] cycloadducts 5a). By contrast, 1b(?+) follows pathway i, leading to trans-stilbene radical cation (2b(?+)) and thiobenzophenone.     

Understanding the mechanisms of [3+2] cycloaddition reactions. The pseudoradical versus the zwitterionic mechanism

Analysis of 12 three-atom-components (TACs) participating in [3+2] cycloaddition (32CA) reactions towards ethylene and acetylene allows establishing good correlations between the pseudodiradical character, the hardness η, and the nucleophilicity N index of the TAC with the feasibility of these non-polar reaction. These results allow the introduction of the pr index, which comprises the two aforementioned DFT reactivity indices. The increase of the pr index for an allylic-type TAC goes accompanied by a linear decrease of the activation enthalpy of the reaction. The present study makes it possible to establish a useful classification of 32CA reactions into zw-type reactions involving TACs with a high zwitterionic character, and pr-type reactions involving TACs with a high pseudodiradical character.     

Hybrid Transported-Tabulated Strategy to Downsize Detailed Chemistry for Numerical Simulation of Premixed Flames

A strategy to introduce hydrocarbon combustion detailed chemistry into three-dimensional numerical simulation of flames is reported. Significant progress has been made recently in terms of accuracy and robustness in both chemical kinetics and flow computations. However, the highest resolution reached in simulation of practical burner does not yet ensure that the response of intermediate radical species is fully captured. In the method discussed, the full set of species and elementary reaction rates of the detailed mechanism are retained, but only species featuring non-zero concentration in fresh and burnt gases are transported with the flow. Intermediate chemical species, developing within thin flame layers, are expressed resorting to their self-similar properties observed in a series of canonical combustion problems, projected into an optimized progress variable defined from all transported species. The method is tested with success in various adiabatic and non-adiabatic laminar steady- and unsteady-strained premixed flames.     

Steric interactions controlling the syn diastereofacial selectivity in the [3 + 2] cycloaddition reaction between acetonitrile oxide and 7‐oxanorborn‐5‐en‐2‐ones: A molecular electron density theory study

A Molecular Electron Density Theory study of the zw‐type 32CA reactions of acetonitrile oxide (NO) with two 7‐oxanorborn‐5‐en‐2‐ones (ONBs) has been performed at the DFT B3LYP/6‐31G(d) computational level. These cycloadditions proceed through one‐step mechanisms with high activation energies and present low para regio and complete syn diastereofacial selectivities. While the non‐polar character of these zw‐type 32CA reactions, which is the consequence of the insufficient electrophilic activation of ONBs, according to the analysis of the conceptual DFT reactivity indices, accounts for the high activation energies, and low para regioselectivity, NCI topological analyses at the anti/syn pairs of para TSs reveal that the steric hindrance encountered between the NO framework and the ONB side containing the carbonyl group along the anti approach mode is responsible for the complete syn diastereofacial selectivity.