High-accuracy theoretical study on the thermochemistry of several formaldehyde derivatives

In the case of several formaldehyde derivatives, with importance in atmospheric and combustion chemistry, the currently available thermochemical values suffer from considerably large uncertainties. In this study a high-accuracy theoretical model chemistry has been used to provide accurate thermochemical data including heats of formation at 0 and 298 K and standard molar entropies at 298 K for CF(2)O, FCO, HFCO, HClCO, FClCO, HOCO, and NH(2)CO. For most of the thermochemical quantities studied here, this investigation delivers the best available estimate.     

Thermochemical approach to solid-state decomposition reactions against the background of traditional theories

The novel thermochemical and traditional Arrhenius approaches to solid-state decomposition reactions have been evaluated from the standpoints of the number and the validity of the assumptions introduced in the theories, and achievements obtained over the last decade in the frameworks of both approaches. As it follows from the analysis, in both respects, the thermochemical approach is preferable. The so-called ‘controversial’ problem of the use of thermodynamic concepts and thermochemical data for the quantitative evaluation of decomposition kinetics in the thermochemical approach has also been discussed.     

Resolution of two-way data: theoretical background and practical problem-solving Part 1: Theoretical background and methodology

This paper reviews recent progress in the resolution of two-way data obtained from hyphenated instruments. Special emphasis is placed on the solution of practical problems. Methods for estimating the number of chemical components both statistically and visually (the first step in solving the resolution problem) and methods for resolving the pure profiles (the second step in solving the resolution problem) are discussed in detail. To deal with real-world problems, pitfalls in the chemometric analysis of the two-way data from the instrumental measurements are also pointed out. Applications of methods for solving some difficult practical problems in environmental chemistry, pharmaceutical chemistry, and physical chemistry will be discussed in the second part of this paper.     

Resolution of two-way data: theoretical background and practical problem-solving. Part 1: theoretical background and methodology

This paper reviews recent progress in the resolution of two-way data obtained from hyphenated instruments. Special emphasis is placed on the solution of practical problems. Methods for estimating the number of chemical components both statistically and visually (the first step in solving the resolution problem) and methods for resolving the pure profiles (the second step in solving the resolution problem) are discussed in detail. To deal with real-world problems, pitfalls in the chemometric analysis of the two-way data from the instrumental measurements are also pointed out. Applications of methods for solving some difficult practical problems in environmental chemistry, pharmaceutical chemistry, and physical chemistry will be discussed in the second part of this paper.     

Challenges and perspectives of combustion chemistry research

In the past decades, combustion chemistry research grew rapidly due to the development of combustion diagnostic methods,quantum chemistry methods, kinetic theory, and computational techniques. A lot of kinetic models have been developed for fuels from hydrogen to transportation fuel surrogates. Besides, multi-scale research method has been widely adopted to develop comprehensive models, which are expected to cover combustion conditions in real combustion devices. However, critical gaps still remain between the laboratory research and real engine application due to the insufficient research work on high pressure and low temperature combustion chemistry. Besides, there is also a great need of predictive pollutant formation model. Further development of combustion chemistry research depends on a closer interaction of combustion diagnostics, theoretical calculation and kinetic model development. This paper summarizes the recent progress in combustion chemistry research briefly and outlines the challenges and perspectives.     

Structured system in chemistry: comparison with mechanics and biology

The fundamental concept of structured chemical system has been introduced and analysed in this paper. This concept, as in biology but not in physics, is very important in chemistry. In fact, the main chemical concepts (molecule and compound) have been identified as systemic concepts and their use in chemical explanation can only be justified in this approach. The fundamental concept of “environment” has been considered and then the system concept in mechanics, chemistry and biology. The differences and the analogies between the use of the systemic approach in these disciplines have been analyzed and correlated to the general problem of reductionism and complexity perspectives. The inanimate–animate dichotomy can be reconsidered in this new approach. Since the chemical systemic concepts of molecule and compound can be dated to the nineteenth century, chemistry can be considered the first true systemic science and its historical evolution can be a model for other sciences (such as the humanities) where the systemic concepts are important.     

Thermochemical characteristics of chitosan–polylactide copolymers

The energies of combustion of chitosan and its block-copolymers with different polylactide contents are determined in a static bomb calorimeter. Standard enthalpies of combustion and formation are calculated for these substances. The dependences of the thermochemical characteristics on block-copolymer composition are determined and discussed.     

Accurate thermochemistry of hydrocarbon radicals via an extended generalized bond separation reaction scheme

Detailed knowledge of hydrocarbon radical thermochemistry is critical for understanding diverse chemical phenomena, ranging from combustion processes to organic reaction mechanisms. Unfortunately, experimental thermochemical data for many radical species tend to have large errors or are lacking entirely. Here we develop procedures for deriving high-quality thermochemical data for hydrocarbon radicals by extending Wheeler et al.'s "generalized bond separation reaction" (GBSR) scheme (J. Am. Chem. Soc., 2009, 131, 2547). Moreover, we show that the existing definition of hyperhomodesmotic reactions is flawed. This is because transformation reactions, in which one molecule each from the predefined sets of products and reactants can be converted to a different product and reactant molecule, are currently allowed. This problem is corrected via a refined definition of hyperhomodesmotic reactions in which there are equal numbers of carbon-carbon bond types inclusive of carbon hybridization and number of hydrogens attached. Ab initio and density functional theory (DFT) computations using the expanded GBSRs are applied to a newly derived test set of 27 hydrocarbon radicals (HCR27). Greatly reduced errors in computed reaction enthalpies are seen for hyperhomodesmotic and other highly balanced reactions classes, which benefit from increased matching of hybridization and bonding requirements. The best performing DFT methods for hyperhomodesmotic reactions, M06-2X and B97-dDsC, give average deviations from benchmark computations of only 0.31 and 0.44 (±0.90 and ±1.56 at the 95% confidence level) kcal/mol, respectively, over the test set. By exploiting the high degree of error cancellation provided by hyperhomodesmotic reactions, accurate thermochemical data for hydrocarbon radicals (e.g., enthalpies of formation) can be computed using relatively inexpensive computational methods.     

Chemie im Motor: Verbrennungsmotoren versus Brennstoffzelle und Elektromotor

This article draws a bow from the fundamentals of the flame chemistry to combustion in engines. Aspects of radical chemistry, pollutant formation and combustion are highlighted. Concepts of current and future internal combustion engines are presented. A main focus lies on pollutant formation and reduction (CO₂, CO, NO_x, HC and soot). Finally, a vision of the future role of the internal combustion engine with respect to fuel cell and electrical engine is outlined.     

Theoretical studies on the unimolecular decomposition of propanediols and glycerol

Polyols, a typical type of alcohol containing multiple hydroxyl groups, are being regarded as a new generation of a green energy platform. In this paper, the decomposition mechanisms for three polyol molecules, i.e., 1,2-propanediol, 1,3-propanediol, and glycerol, have been investigated by quantum chemistry calculations. The potential energy surfaces of propanediols and glycerol have been built by the QCISD(T) and CBS-QB3 methods, respectively. For the three molecules studied, the H(2)O-elimination and C-C bond dissociation reactions show great importance among all of the unimolecular decomposition channels. Rate constant calculations further demonstrate that the H(2)O-elimination reactions are predominant at low temperature and pressure, whereas the direct C-C bond dissociation reactions prevail at high temperature and pressure. The temperature and pressure dependence of calculated rate constants was demonstrated by the fitted Arrhenius equations. This work aims to better understand the thermal decomposition process of polyols and provide useful thermochemical and kinetic data for kinetic modeling of polyols-derived fuel combustion.     

Theory of solid-state thermal decomposition reactions

A case is presented to recommend strongly that scientists interested in thermal chemistry should make comprehensive, conscientious, clinical and critical analyses of the strengths and weaknesses of The L??vov Thermochemical Theory (L??vov, Thermal decomposition of solids and melts??new thermochemical approach to the mechanism, kinetics and methodology, Springer, Berlin, 2007), used to interpret the kinetics and mechanisms of reactions that occur on heating. The shortcomings underlying the theory (some originally developed for solid decompositions) currently uncritically accepted in this field are reviewed, and these deficiencies are contrasted with the successes of L??vov??s approach. To promote the use of this alternative theory, features that may have discouraged researchers unfamiliar with its assumptions, methodology and applications are discussed here. A new scientific theory cannot be ignored or discounted without adequate consideration and testing, particularly in a stagnant area of chemistry that lacks guiding principles and unifying concepts. Novel ideas in the literature (L??vov 2007) deserve recognition, critical appraisal and, if possible, exploitation to maintain the progress of scientific research.     

Ab initio aqueous thermochemistry: application to the oxidation of hydroxylamine in nitric acid solution

Ab initio molecular orbital calculations were performed and thermochemical parameters estimated for 46 species involved in the oxidation of hydroxylamine in aqueous nitric acid solution. Solution-phase properties were estimated using the several levels of theory in Gaussian03 and using COSMOtherm. The use of computational chemistry calculations for the estimation of physical properties and constants in solution is addressed. The connection between the pseudochemical potential of Ben-Naim and the traditional standard state-based thermochemistry is shown, and the connection of these ideas to computational chemistry results is established. This theoretical framework provides a basis for the practical use of the solution-phase computational chemistry estimates for real systems, without the implicit assumptions that often hide the nuances of solution-phase thermochemistry. The effect of nonidealities and a method to account for them is also discussed. A method is presented for estimating the solvation enthalpy and entropy for dilute aqueous solutions based on the solvation free energy from the ab initio calculations. The accuracy of the estimated thermochemical parameters was determined through comparison with (i) enthalpies of formation in the gas phase and in solution, (ii) Henry's law data for aqueous solutions, and (iii) various reaction equilibria in aqueous solution. Typical mean absolute deviations (MAD) for the solvation free energy in room-temperature water appear to be ~1.5 kcal/mol for most methods investigated. The MAD for computed enthalpies of formation in solution was 1.5-3 kcal/mol, depending on the methodology employed and the type of species (ion, radical, closed-shell) being computed. This work provides a relatively simple and unambiguous approach that can be used to estimate the thermochemical parameters needed to build detailed ab initio kinetic models of systems in aqueous solution. Technical challenges that limit the accuracy of the estimates are highlighted.     

Encoding of polycyclic Si-containing molecules for determining species uniqueness in automated mechanism generation

Automated mechanism generation is an attractive way to understand the fundamental kinetics of complex reaction systems such as silicon hydride clustering chemistry. It relies on being able to tell molecules apart as they are generated. The graph theoretic foundation allows molecules to be identified using unique notations created from their connectivity. To apply this technique to silicon hydride clustering chemistry, a molecule canonicalization and encoding algorithm was developed to handle complex polycyclic, nonplanar species. The algorithm combines the concepts of extended connectivity and the idea of breaking ties to encode highly symmetric molecules. The connected components in the molecules are encoded separately and reassembled using a depth-first search method to obtain the correct string codes. A revised cycle-finding algorithm was also developed to properly select the cycles used for ring corrections when thermodynamic properties were calculated using group additivity. In this algorithm, the molecules are expressed explicitly as trees, and all linearly independent cycles of every size in the molecule are found. The cycles are then sorted according to their size and functionality, and the cycles with higher priorities will be used to include ring corrections. Applying this algorithm, more appropriate cycle selection and more accurate estimation of thermochemical properties of the molecules can be obtained.     

Configurational enthalpy of polystyrene

Recent precision measurements of the heats of combustion of atactic and isotactic polystyrene permit an unequivocal calculation of the enthalpy difference in the bulk amorphous forms of the two isomers of this polymer. Contributions to this quantity arise mainly from the differences in nonbonded interactions in the two configurations but may also contain terms relating to higher energy conformations and to intermolecular interactions. The thermochemical and NMR data of specific polymers and of simple molecules are discussed in a comparison with model compound calculations. The thermochemical method has potentially important applications in studying molecular interactions in stereoregular polymers.     

无机化学四个易混淆基本概念的讲授建议

Fuzzy representation of chemical concepts is an obstacle for learning, and this prevents students from developing strict logical thought. Inorganic chemistry is one of the basic courses for most of first-year undergraduate students of chemistry and related majors. We dissect four common concepts in inorganic chemistry which are easily confused, point out the reasons for the wrong conclusions and give some teaching suggestions. This article helps teachers for clear presentation of these concepts.     

Thermochemical characteristics of cellulose acetates with different degrees of acetylation

The standard enthalpies of combustion and formation of cellulose acetates with different degrees of acetylation are determined. It is established that there is a proportional dependence of these thermochemical characteristics vs. the degree of acetylation, weight fraction of bonded acetic acid, and molar mass of the repeating unit of cellulose acetates.     

Circulation of Concepts

A major obstacle to chemistry being a deductive science is that its core concepts very often are defined in a circular manner: it is impossible to explain what an acid is without reference to the complementary concept of a base. There are many such dual pairs among the core concepts of chemistry. Such circulation of concepts, rather than an infirmity chemistry is beset with, is seen as a source of vitality and dynamism.     

A mechanistic and kinetic study on the decomposition of morpholine

The combustion chemistry of morpholine (C(4)H(8)ONH) has been experimentally investigated recently as a representative model compound for O- and N-containing structural entities in biomass. Detailed profiles of species indicate the self-breakdown reactions prevailing over oxidative decomposition reactions. In this study, we derive thermodynamic and kinetic properties pertinent to all plausible reactions involved in the self-decomposition of morpholine and its derived morphyl radicals as a crucial task in the development of comprehensive combustion mechanism. Potential energy surfaces have been mapped out for the decomposition of morpholine and the three morphyl radicals. RRKM-based calculations predict the self-decomposition of morpholine to be dominated by 1,3-intramolecular hydrogen shift into the NH group at all temperatures and pressures. Self-decomposition of morpholine is shown to provide pathways for the formation of the experimentally detected products such as ethenol and ethenamine. Energetic requirements of all self-decomposition of morphyl radicals are predicted to be of modest values (i.e., 20-40 kcal/mol) which in turn support the occurrence of breaking-down reactions into two-heavy-atom species and the generation of doubly unsaturated four-heavy-atom segments. Calculated thermochemical parameters (in terms of standard enthalpies of formation, standard entropies, and heat capacities) and kinetic parameters (in terms of reaction rate constants at a high pressure limit) should be instrumental in building a robust kinetic model for the oxidation of morpholine.     

Pyrazolyltetrazoles—a High-Enthalpy Backbone for Designing High-Energy Compounds: An Experimental Study of the Enthalpy of Formation

The standard enthalpies of combustion and formation of isomeric nitropyrazolyltetrazoles have been measured by combustion calorimetry. Positional isomerism has been shown to have a significant effect on thermochemical characteristics. The contributions of some explosophore groups and moieties to the total heat content of the molecules have been determined. These contributions can be used to correctly calculate the enthalpy of formation of both known and hypothetical energy-intensive compounds.     

《高分子化学》教学中有机化学知识的有效利用探索

高分子化学和有机化学紧密相连,后者是学习前者的基础.在高分子化学教学中,有效利用有机化学知识解释聚合物的一些概念,将有助于学生更好的理解和掌握高分子化学知识.本文根据教学实践,介绍了几点利用有机化学知识帮助解释高分子化学中的概念或反应的实例,并对教材中存在的疑点提出了自己的看法.