Nitração do fenol, um método em escala semi-micro para disciplina prática de 4 horas

A procedure for the nitration of phenol in a semi-micro scale, followed by separation of the formed orto- and para-nitrophenol isomers by column chromatography, is described. All the experiment, including determination of the melting point of the isolated products, require a period of 4 hours, and it is suitable for organic chemistry laboratory undergraduate courses.

Nitração aromática: substituição eletrofílica ou reação com transferência de elétrons?

Aromatic nitration is one of the most relevant class of reactions in organic chemistry. It has been intensively studied by both experimental, including works in the condensed as well as in the gas phase, and theoretical procedures. However, the published results do not seem to converge to an unique mechanism. Electrophilic substitution and electron transfer, in an exclusive way, are both proposed as the main mechanism for the reaction. We review these proposals and discuss the most recent findings.

Compostos alfa-diazo carbonílicos: uma estratégia atraente para a síntese orgânica

Diazocarbonyl compounds are a very important class of organic substances which have a long history of useful aplications in organic chemistry. The focus of this report deals with the use of diazocarbonyl compounds in a ariety of important reactions and their application in organic synthesis. These reactions are briefly summarized showing their broad scope.

Vinte e cinco anos de reações, estratégias e metodologias em Química Orgânica

An overview of the developments that occurred in the field of organic chemistry in Brazil in the last 25 years is presented. These developments are briefly compared to those observed worldwide, including some modern trends. The main source of information was the annual meeting of the Brazilian Chemical Society (RASBQ) covering the period 1979-2001 and the biennial Brazilian Meeting on Organic Synthesis (BMOS). All the contributions presented at these two meetings were classified according to six main indicatives, to permit a discussion about the past, present and future activities of Organic Chemistry in Brazil.

A extração de cafeína em bebidas estimulantes: uma nova abordagem para um experimento clássico em química orgânica

Caffeine extraction procedures from water soluble and water insoluble materials for preparing stimulating beverages are described. Water soluble materials used were instant tea and coffee and water insoluble materials were, among others, guaraná powder and maté leaves. The extraction of caffeine from water soluble materials, especially instant tea, is more suitable for an organic chemistry teaching laboratory than the classic experiment using tea leaves, due to the economy of time and a larger amount of extracted caffeine. The procedure is time-saving and requires only a four-hour period. The experiments illustrate the extraction process as used in undergraduate organic chemistry laboratories.

Síntese do isobutileno e seu emprego em reações de esterificação: propostas de aulas práticas de química orgânica para a graduação

An experiment for the synthesis of isobutylene from tert-butanol dehydratation using oxalic acid as catalyst, followed by preparations of tert-butyl benzoate and tert-butyl cinnamate is described. The synthesis are simple, requiring two periods of 4 hours and are suitable for undergraduate organic chemistry experimental courses.

Inserção do conceito de economia atômica no programa de uma disciplina de química orgânica experimental

In this paper, the atom economy concepts are applied in a series of experiments during an experimental organic chemistry class, to implement "green chemistry" in an undergraduate course.

Sucroquímica: síntese e potencialidades de aplicações de alguns derivados químicos de sacarose

The interest on the use of sucrose as raw material increased in the last years. In this work, the synthesis and applications of sucrose derivatives as esters, ethers, and other products are discussed in a concise manner aiming to presenting the sucrochemistry as a promising field in organic chemistry from a rather accessible, low-priced, ecological, and renewable source.

Estabilidade relativa de alcenos: análise dos critérios encontrados nos livros textos de graduação e uma proposta de explicação operacional para alcenos dissubstituídos

Despite of being used as thermodynamic criterion to rank alkene stability in a number of undergraduate textbooks, the heat of hydrogenation does not describe adequately the relative stability of disubstituted alkenes. In this work, both the heat of formation and the heat of combustion were used as thermodynamic criteria to rank correctly the stability of alkenes according to the degree of alkyl substitution and also in the disubstituted series (geminal > trans > cis). An operational model based on molecular orbital and valence bond representations of hyperconjugation is proposed to show how this effect can explain the order of stability of this class of compounds.

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.

Extração de pigmentos das sementes de Bixa orellana L.: uma alternativa para disciplinas experimentais de química orgânica

This paper describes methodologies for the extraction and characterization by TLC, UV-VIS, IR and NMR of bixin from Bixa orellana L. (urucum) seeds. Based on the results, the extraction with NaOH 5% is the fastest, uses low-cost materials, requires two to four laboratory hours and is a useful alternative for an experimental Organic Chemistry discipline.

Craqueamento térmico de alcanos: uma aula prática de química orgânica para a graduação

In this work we describe an experiment for the thermal cracking of octane and heptane and the qualitative analyses of the products using the Baeyer test for unsaturated compounds and gas chromatographic analyses. The experiment is very simple and requires one period of two hours and is suitable for undergraduate organic chemistry experimental courses.

Atualizando a química orgânica experimental da licenciatura

The present contribution describes three different modern experiments for possible adoption in undergraduate organic chemistry laboratories. These are: 1. electrocatalytic hydrogenation of benzaldehyde to benzyl alcohol; 2. identification of three volatile components, obtained from pineapple fruit, by mass spectrometry and 3. microwave mediated fast synthesis of N-(p-chlorophenyl)phthalamic acid from phthalic anhydride and p-chloroaniline under solvent-free conditions. The experiments can be executed in a short period of time, putting the undergraduate student in contact with a variety of topics in organic chemistry and several techniques of analysis, showing multidisciplinarity in organic chemistry.

Simulação de desdobramentos complexos de espectros de RMN de ¹H

Complex ¹H NMR spectra multiplets that cannot be easily understood by simple inspection are rather frequent in the daily work of the organic chemistry analyst. The multiple and excellent new techniques available from modern instruments usually provide satisfactory solutions, but there are still many cases where a simulation is necessary, at least to obtain a final confirmation. It is extremely convincing to see that a graph, obtained by calculations with chemical-shift and coupling-constant values only, can be virtually identical to the experimental spectrum. This paper describes a computer program to make such calculations. The program is free and can be downloaded from http://artemis.ffclrp.usp.br/NMR.htm (click on SimEsp_NMR_Compil.zip). All routines are also available and may be used without any restrictions. The paper includes a fairly detailed discussion about how the calculations are made.

Espectroscopia de Ressonância Magnética Nuclear de 13C no estudo de rotas biossintéticas de produtos naturais

During the last five decades, as a result of an interaction between natural product chemistry, synthetic organic chemistry, molecular biology and spectroscopy, scientists reached an extraordinary level of comprehension about the natural processes by which living organisms build up complex molecules. In this context, 13C nuclear magnetic resonance spectroscopy, allied with isotopic labeling, played a determinant role. Nowadays, the widespread use of modern NMR techniques allows an even more detailed picture of the biochemical steps by accurate manipulation of the atomic nuclei. This article focuses on the development of such techniques and their impact on biosynthetic studies.