Esquema geral para elucidação de substâncias orgânicas usando métodos espectroscópico e espectrométrico

This work describes a systematic method to be applied in undergraduate courses of organic chemistry, correlating infrared spectra, hydrogen and carbon-13 nuclear magnetic resonance, and mass spectra. To this end, a scheme and a table were developed to conduct the elucidation of the structure of organic compounds initially using infrared spectra. Interpretation of hydrogen and carbon-13 nuclear magnetic resonance spectra and of mass spectra is used to confirm the proposed structure.

Synthesis and antiprotozoal activity of oligomethylene- and p-phenylene-bis(methylene)-linked bis(+)-huprines

We have synthesized a series of dimers of (+)-(7R,11R)-huprine Y and evaluated their activity against Trypanosoma brucei, Plasmodium falciparum, rat myoblast L6 cells and human acetylcholinesterase (hAChE), and their brain permeability. Most dimers have more potent and selective trypanocidal activity than huprine Y and are brain permeable, but they are devoid of antimalarial activity and remain active against hAChE. Lead optimization will focus on identifying compounds with a more favourable trypanocidal/anticholinesterase activity ratio.

Synthesis and antiprotozoal activity of oligomethylene- and p-phenylene-bis(methylene)-linked bis(+)-huprines

We have synthesized a series of dimers of (+)-(7R,11R)-huprine Y and evaluated their activity against Trypanosoma brucei, Plasmodium falciparum, rat myoblast L6 cells and human acetylcholinesterase (hAChE), and their brain permeability. Most dimers have more potent and selective trypanocidal activity than huprine Y and are brain permeable, but they are devoid of antimalarial activity and remain active against hAChE. Lead optimization will focus on identifying compounds with a more favourable trypanocidal/anticholinesterase activity ratio.

Larock Reaction in the synthesis of heterocyclic compounds

The indole ring is one of the most common features in natural products and small molecules with important bioactivity. Larock reported a new methodology for the synthesis of the indole ring system based on the palladium-catalyzed heteroannulation of 2-iodoaniline and substituted alkyne moieties. This procedure was subsequently extended to the preparation of other nitrogen- and oxygen- containing heterocycles. This is the process of choice for the synthesis of a large number of heterocyclic derivatives, as it provides outstanding regioselectivity and good to excellent yields.

Larock Reaction in the synthesis of heterocyclic compounds

The indole ring is one of the most common features in natural products and small molecules with important bioactivity. Larock reported a new methodology for the synthesis of the indole ring system based on the palladium-catalyzed heteroannulation of 2-iodoaniline and substituted alkyne moieties. This procedure was subsequently extended to the preparation of other nitrogen- and oxygen- containing heterocycles. This is the process of choice for the synthesis of a large number of heterocyclic derivatives, as it provides outstanding regioselectivity and good to excellent yields.

Cânfora: um bom modelo para ilustrar técnicas de RMN

The use of Nuclear Magnetic Resonance spectroscopy to establish the three-dimensional structures of molecules is an important component of modern Chemistry courses. The combination of techniques that can be used for this purpose is conveniently illustrated by their application to the camphor molecule. This paper presents applications of several techniques used in NMR spectral interpretation in an increasing order of complexity. The result of individual experiments is illustrated in order to familiarize the user with the way connectivity through bonds and through space is established from 1D/2D-NMR spectra and molecular stereochemistry is determined from different NMR experiments.

Extração de β-caroteno de cenouras: uma proposta para disciplinas experimentais de química

This paper reports on the development of a simple and fast procedure for β-carotene extraction from carrots and its quantification by UV/Vis spectroscopy. Carotenoids extracted from carrots may also be used as alternative reagents for TLC (thin layer chromatography) detection of natural compounds with antioxidant properties, replacing the commercial p.a. grade β-carotene. Although this reagent had around 10% b-carotene, it proved to be as efficient for TLC analysis as the commercial p.a. grade β-carotene. This practice is a useful alternative for teaching undergraduate organic chemistry laboratory classes.

Cloração do anisol, tolueno e nitrobenzeno com ácido tricloroisocianúrico (ATCI): aspectos computacionais sobre a reatividade e regiosseletividade

We present in this educational article a theoretical analysis based on DFT/B3LYP 6-311++G (d,p) and ab initio MP2/6-311++G(d,p) computational calculation about the reactivity and the regioselectivity on the chlorination reaction of anisole, toluene and nitrobenzene, using trichloroisocyanuric acid (TICA) as donor of Cl+. The H.O.M.O. / L.U.M.O. energy and N.B.O. atomic charges of various aromatic systems were calculated in ab initio level. The energies of the reagents and intermediaries were calculated using D.F.T.. These results have been presented as a quantitative example for the S E A mechanism, in the undergraduate organic chemistry disciplines.

A química orgânica na consolidação dos conceitos de átomo e molécula

The present work discusses the appearance of the concepts of valence and molecular structure, and describes the appropriation and evolution of the concept of molecule in the period following the publication of Avogadro's Hypothesis. The point of reference is the development of what became known as Organic Chemistry, which encompassed Pharmacy, Physiological Chemistry, Animal and Plant Chemistry, Chemistry of Dyestuffs, Agricultural Chemistry, and the fledgling Organic Synthesis industry in the early 19th century. The theories formulated in these areas and the quest for accurate atomic weights led to those concepts of valence and molecular structure and to a precise differentiation between atom and molecule.

Aspectos mecanísticos da bioatividade e toxicidade de nitrocompostos

Nitrocompounds are bioactive molecules used as antibacterial, antiparasitic and antitumoral agents. In the past of years, these molecules have been broadly studied in several fields, such as medicinal chemistry, organic chemistry, biochemical, toxicology and electrochemistry. The nitrocompounds mode of action involves the biotransformation of the nitro group, releasing intermediates in the redox process. Some of those intermediates attack enzymes, membranes and DNA, providing the basis for their biological activity and adverse effects. In this report, some aspects regarding the biological activity, mechanism of action and toxicity of nitrocompounds are explored, purposing the research of new bioactive derivatives having low toxicity.

Extração e purificação de clorofila a, da alga Spirulina maxima: um experimento para os cursos de química

This work describes a simple and economical experiment for the extraction and purification of chlorophyll a from Spirulina maxima. Extraction and purification of natural compounds can be considered one of the most illustrative experiments that can be performed in Organic Chemistry courses. Particularly, the chromatography of dyes and pigments allows students to have a better comprehension of the chromatography separations. These compounds represent an important class of organic pigments applied in pharmaceutical, cosmetic, detergent compositions, and various other fields and can be extracted from plants and algae. To extract, separate and purify chlorophyll a from associated pigments such as xanthophylls, carotenes, and pheophytins, very costly processes are reported. The present approach is perfectly adequate for use in Chemistry experiments for undergraduate students.

Óleo essencial de limão no ensino da cromatografia em camada delgada

This paper describes a simple experiment employing the essential oil of limes which can be applied in undergraduate organic chemistry laboratory classes for the teaching of thin layer chromatography (TLC). The experiment consists in submit lime peel oil to TLC separation employing hexane and dichloromethane as the eluents and five different systems for visualization of the chromatogram. In one experiment it is possible to teach the different variables of the TLC technique. This experiment may also be performed following vapor distillation and liquid-liquid extraction technique in experimental classes.

Aplicação de α-oxoceteno ditiocetais em síntese orgânica

The synthesis and reactivity of α-oxoketenes dithioacetals (S,S-acetals), general structure [(R¹C=OC(R²)=C(SR³)(SR4)], are reported. We also showed the application of S,S acetals as synthons for efficient synthesis of isoxazoles, pyrazoles, indazoles, thiophenes, dithiol thiones, pyridines, pyrimidines and other heterocycles. This work aims to review the importance of α-oxoketenes dithioacetals in organic chemistry during the past few years.

El aprendizaje basado en problemas como estrategia para el cambio metodológico en los trabajos de laboratorio

The Problem Based Learning (PBL) can be used as a strategy for methodological change in conventional learning environments. In this paper, the integration of laboratory work in PBL grounded activities during an introductory organic chemistry course is described. The most decisive issues of their implementation are discussed. The results show how this methodology favours the laboratory work contextualization in subject-matter and promotes the Science-Technology-Society-Environment relationships. Besides, it contributes to competence development like planning and organization skills, information search and selection, cooperative work, etc., the same way as the tutorial action improvement.

A Química Quântica na compreensão de teorias de Química Orgânica

Quantum chemical calculations were performed in order to obtain molecular properties such as electronic density, dipole moment, atomic charges, and bond lengths, which were compared to qualitative results based on the theories of the organic chemistry. The quantum chemistry computational can be a useful tool to support the main theories of the organic chemistry.