Implications, large and small, from chemical education research for the teaching of chemistry

Research studies in chemical education pose a communication problem for chemists. Unlike the findings from other specializations in chemistry the findings in chemical education tend to be reported in education journals that are not readily accessible to most chemists or chemistry teachers. This lecture is an attempt to remedy this gap in communication. Research studies fall into three broad categories. (i) issues related to the content of chemistry itself, that is, What content to teach? And What meaning of each topic is to be conveyed? (ii) issues related to how chemical content is taught, such as, the role of lectures, practical work, particular pedagogies, etc. and (iii) issues related to its learning, that is, learning of concepts, conceptual change, motivation, etc. Findings in each of these categories of research over the last twenty years have drawn attention to opportunities for improving the quality of chemical education in each of the levels of formal education where chemistry is taught. Sometimes the research findings seem small since they, in fact, merely diagnose the actual problem in teaching and learning. At other times, the research findings are large because they provide a solution to these problems. What remains to be done is to disseminate the findings so that appropriate teaching occurs more widely, with its consequent gains in the quality of learning. Research findings, of these small and large types will be used to illustrate the potential of research to make the practice of chemical education more effective.

Gas-phase ion chemistry of silyl cations obtained from hexamethyldisilazane

The gas-phase ion-molecule reactions of the Me3SiN(H)SiMe2+ ion, obtained by electron ionization from Me3SiN(H)SiMe3, have been studied in a Fourier transform ion cyclotron resonance spectrometer in order to understand the mechanistic details of an important chemical system presently used in film formation. This silyl cation has been observed to undergo addition reactions at electron rich centers to form stable adducts that may undergo further methane elimination in the case of alcohols and amines. The most important feature of these reactions is the fact that a metathesis type reaction can be observed in the presence of H2O, and other hydrogen labile substrates like alcohols, leading to the formation of the corresponding oxygen-containing ion, i.e. Me3SiOSiMe2+. For alcohols (ROH), facile formation of a tertiary product ion, presumably corresponding to an Me3Si-O-Si(Me)=O+-R structure with elimination of an amine reveals the strong tendency of these nitrogen-containing ions to undergo metathesis type reactions with oxygen containing substrates.

"Green chemistry": os 12 princípios da química verde e sua inserção nas atividades de ensino e pesquisa

Green chemistry ¾ defined as the design, development, and application of chemical processes and products to reduce or eliminate the use and generation of substances hazardous to human health and the environment. This article summarizes the 12 principles of green chemistry, describing how they have been applied to the academic, industrial and research activities around the world.

O método das trajectórias clássicas: colisões coplanares do tipo A+BC

The general methodology of classical trajectories as applied to elementary chemical reactions of the A+BC type is presented. The goal is to elucidate students about the main theoretical features and potentialities in applying this versatile method to calculate the dynamical properties of reactive systems. Only the methodology for two-dimensional (2D) case is described, from which the general theory for 3D follows straightforwardly. The adopted point of view is, as much as possible, that of allowing a direct translation of the concepts into a working program. An application to the reaction O(¹D)+H2->O+OH with relevance in atmospheric chemistry is also presented. The FORTRAN codes used are available through the web page www.qqesc.qui.uc.pt.

The chemistry involved in the steam treatment of lignocellulosic materials

Pretreatment of lignocellulosic materials is essential for bioconversion because of the various physical and chemical barriers that greatly inhibit their susceptibility to bioprocesses such as hydrolysis and fermentation. The aim of this article is to review some of the most important pretreatment methods developed to date to enhance the conversion of lignocellulosics. Steam explosion, which precludes the treatment of biomass with high-pressure steam under optimal conditions, is presented as the pretreatment method of choice and its mode of action on lignocellulosics is discussed. The optimal pretreatment conditions for a given plant biomass are defined as those in which the best substrate for hydrolysis is obtained with the least amount of soluble sugars lost to side reactions such as dehydration. Therefore, pretreatment optimization results from a compromise between two opposite trends because hemicellulose recovery in acid hydrolysates can only be maximized at lower pretreatment severities, whereas the development of substrate accessibility requires more drastic pretreatment conditions in which sugar losses are inevitable. To account for this heterogeneity, the importance of several process-oriented parameters is discussed in detail, such as the pretreatment temperature, residence time into the steam reactor, use of an acid catalyst, susceptibility of the pretreated biomass to bioconversion, and process design.

NMR investigation and theoretical calculations of the effect of solvent on the conformational analysis of 4',7-di-hydroxy-8-prenylflavan

The NMR conformational study of 4',7-di-hydroxy-8-prenylflavan 1 was carried out in acetone-d6, DMSO-d6 and CDCl3 which enabled the proposition of three conformations, namely 1a, 1b and 1c, differing in the position of the prenyl group. Geometry optimizations performed using AM1 method showed that 1a (deltaHf = -86.2 kcal/mol) is as stable as 1b (deltaHf = -85.1 kcal/mol) and 1c (deltaHf = -85.4 kcal/mol). When the solvent was included, the calculations showed that the solute-solvent interactions could be explained either in the light of the electronic intermolecular delocalization or the electrostatic character between solute and solvent. Theoretical calculations (HF/6-31G*, deltaFT/BLYP/6-31G*, and deltaFT/B3LYP/6-31G*) showed that the combination of these types of interactions present in each solute-solvent system, dependent on the chemical properties of the solvent, lead to different spatial arrangements of the prenyl group, which in turn determined the conformation of 1.

Adaptação no método do peso da gota para determinação da tensão superficial: um método simplificado para a quantificação da CMC de surfactantes no ensino da química

The discussion based on surfactant cleaning action is commonly used in chemistry classrooms for the comprehension of theoretical concepts related to surface tension and micelle formation. The experimental quantification of surface tension of aqueous solutions of surfactants provides the practical instruments for this discussion. The present paper describes a simplification on the common apparatus employed for the drop-weight method, making the determination of surface tension accessible to any chemistry lab. The surface tension of various liquids and the critical micelle concentration, CMC, of three commercial surfactants were measured with this modified method, and proved to be consistent with literature values.

Esquema para interpretação de espectros de substâncias orgânicas na região do infravermelho

This article decribes a simple and systematic method to interpret an infrared spectrum using a flow chart to elucidate the structure of a simple organic compound. It is aimed at undergraduate courses of organic chemistry to make beginners proficient. The proposed flow chart for infrared spectrum interpretation and characterization of organic compounds is suitable for theoretical and experimental courses.

Experimentos didáticos envolvendo radiação microondas

Theoretical and practical aspects of the use of microwave-assisted strategies in chemistry are introduced for students using simple and safe experiments employing a domestic oven. Three procedures are proposed for evaluating the distribution of microwave radiation inside the microwave oven cavity: (1) variation of the volume of marshmallows; (2) drying of filter paper wetted with Co(II) solution, and (3) variation of water temperature, after microwave-assisted heating. These experiments establish the position with the highest incidence of microwave radiation in the oven cavity, which was chosen for the synthesis of salicylic acid acetate. This synthesis was performed in 5 min of heating and the yield was around 85%. All experiments can be carried out in a 4 h lab-session using low-cost instrumentation.

The saccharinate anion: a versatile and fascinating ligand in coordination chemistry

The saccharinate anion, obtained by deprotonation of the N-H moiety of saccharin (o-sulfobenzimide) is a very versatile and polyfunctional ligand in coordination chemistry. In this review the different forms of metal-to-ligand interactions involving this anion and some other coordination peculiarities are briefly discussed on the basis of some selected examples.

Do general chemistry textbooks facilitate conceptual understanding?

Research in chemistry education has recognized the need for facilitating students' understanding of different concepts. In contrast, most general chemistry curricula and textbooks not only ignore the context in which science progresses but also emphasize rote learning and algorithmic strategies. A historical reconstruction of scientific progress shows that it inevitably leads to controversy and debate, which can arouse students' interest and thus facilitate understanding. The objective of this article is to review research related to the evaluation of general chemistry textbooks (based on history and philosophy of science, HPS) and suggest alternatives that can facilitate conceptual understanding.

Preparo da para-cloroanilina: um experimento simples, rápido e barato

Experiments simple, short and efficient for experimental disciplines in undergraduate courses in Chemistry are an excellent opportunity for students to consolidate the learning of theoretical concepts in classical chemical transformations. The use of a safe reagent, of low cost and easy access is the motivation for this communication, that describes the use of trichloroisocyanuric acid - a chlorinating agent used in the treatment of swimming pool water - for the chlorination of acetanilide, an intermediate in the preparation of para-chloroaniline.

Aplicação da química quântica computacional no estudo de processos químicos envolvidos em espectrometria de massas

The field of application of mass spectrometry (MS) has increased considerably due to the development of ionization techniques. Other factors that have stimulated the use of MS are the tandem mass spectrometry (MS/MS) and sequential mass spectrometry (MSn) techniques. However, the interpretation of the MS/MS and MSn data may lead to speculative conclusions. Thus, various quantum chemical methods have been applied for obtaining high quality thermochemical data in gas phase. In this review, we show some applications of computational quantum chemistry to understand the formation and fragmentation of gaseous ions of organic compounds in a MS analysis.

O ensino de reações orgânicas usando química computacional: I. reações de adição eletrofílica a alquenos

Basic concepts that play an important role in some organic reactions are revisited in this paper, which reports a pedagogical experience involving undergraduate and graduate students. A systematic procedure has been applied in order to use widespread available computational tools. This paper aims to discuss the use of computers in teaching electrophilic addition reactions to alkenes. Two classical examples have been investigated: addition to non-conjugated alkenes and addition to conjugated dienes. The results were compared with those normally discussed in organic textbooks. Several important concepts, such as conformational analysis and energy control (kinetic and thermodynamic) involved in reaction mechanisms can be taught more efficiently if one connects theoretical and practical tools.

Concepções e ações de formadores de professores de química sobre o estágio supervisionado: propostas brasileiras e portuguesas

The purpose of this paper is to investigate lecturers'actions and conceptions about pre-service teaching practices in chemistry. In this sense, it takes into account several theoretical references concerned with teacher education, which support the qualitative analysis of 18 interviews, gathered with 14 brazilian and 4 portuguese lecturers. Results reveal that the pre-service teaching practices in chemistry have been performed far from a technical approach, showing a paradigmatic rupture and presenting another logic related with teacher education in chemistry, which have improved the comprehension of the teachers' real practices, since these have been shaped by complex and unprescribed factors.