a modo de experiencia en el ámbito de la enseñanza universitaria. Para ello, se adaptaron estrategias utilizadas en otros niveles educativos, en especial en lo concerniente a respetar los estilos de trabajo de las docentes implicadas. Se desarrolló un sitio Web exclusivo para este grupo, con materiales didácticos especialmente diseñados. Todos los actores implicados, profesoras y alumnos, mostraron un alto grado de satisfacción con esta nueva estrategia didáctica, por lo que amerita ser continuada y ampliada a otros cursos universitarios.
Monoarylhydrazones of α-Lapachone: Synthesis, Chemical Properties and Antineoplastic Activity. -(RENOU*, S. G.; ASIS, S. E.; ABASOLO, M. I.; BEKERMAN, D. G.; BRUNO, A. M.; Pharmazie 58 (2003) 10, 690-695; Dep. Quim.
Resumen: Una clase de química puede ser considerada como un espacio de comunicación entre el docente experto y los estudiantes novatos, donde los lenguajes utilizados son la interfase explícita y observable del intercambio comunicativo. En el presente trabajo se muestra con dos ejemplos cómo la diversidad de lenguajes químicos en lugar de favorecer la comprensión de los estudiantes, puede actuar como fuente de obstáculos que dificultan la comunicación en el aula. Así mismo, se analizará con otros dos ejemplos cómo el discurso con el que se enseña la disciplina también es potencial generador de errores en los estudiantes, cuando ellos construyen sus modelos mentales idiosincrásicos a partir de un discurso recortado y simplificado, desde las mejores intenciones de realizar buenas transposiciones didácticas. Se plantea que un enfoque de análisis de la situación de aula como un encuentro comunicativo entre experto y novato conduce a una necesaria diferenciación entre "hablar química" y "comprender química".Palabras clave: Enseñanza de química. Comunicación. Discurso. Didáctica. Aprendizaje. Abstract:A class of chemistry can be considered as a forum for communication between the expert teacher and novice students, where the languages used are explicit and observable interface of a communicative exchange. In this paper we show, with two examples, how the diversity of chemical languages, instead of promoting student understanding, it can act as a source of barriers to communication in the classroom. Also, will be discussed in two examples how the speech with which the discipline is taught is also generating potential errors in students when they build their idiosyncratic mental models from a cut and simplified speech from the best intentions of make good didactic transpositions. It is argued that an approach to analysis of the situation in the classroom as a communicative encounter between expert and novice leads to a necessary distinction between "talking chemistry" and "understanding chemistry."
Some novel 3‐substituted benzoquinoxalinones [R = H, CH3, C6H5, (CH2)2COOH] were synthesized by the Hinsberg reaction between 2,3‐diaminonaphthalene and several α‐dicarbonyl compounds. The course of the reactions was followed by the second uv/visible Derivative Spectroscopy Method at different pH values (‐0.89 to 9.0) and also in organic solvents at 25°. The compound non‐substituted at C‐3 was the only one that could be obtained in every media in good yields (80%), having pseudo first‐order anelation rate constants of relative high values (1 × 10−1 — 1 × 10−2 min−1). On the other hand, only methanol could be used as the organic solvent for the synthesis of all of the other compounds; aqueous media always provided better results. In the 3‐methyl derivative, as well as in the 3‐phenyl derivative the change of the reaction pH medium modified the stoichiometry of the anelation, turning a non‐quantitative reaction into a quantitative one. This is explained by a change in the mechanism of the reaction on going to lower hydrogen concentrations, a fact that was supported by complementary quantitative hptlc experiments. In general, pseudo first‐order rate constants for the anelation were one or two logarithmic units lower than those of the non‐substituted compound (RC‐3 = H), but yields were above 60% in every case. A reaction scheme is presented which includes a probable mechanism.
Kinetic studies on the anelation of quinoxalinone derivatives 3a‐c and pyrido[2,3‐b]pyrazinone derivatives 5a‐c and 6a‐c synthesized by the Hinsberg reaction is reported. o‐Phenylenediamine or 2,3‐diaminopyridine were treated with bifunctional carbonyl compounds such as glyoxylic, pyruvic and benzoylformic acids under different experimental conditions. When pyridopyrazine derivatives were synthesized both position isomers were achieved applying regioselective reactions. Mixture were avoided by looking for special experimental conditions that led unambiguously to only one of the components of the classic “Hinsberg mixture”. Quinoxalinone derivatives 3a‐c were obtained at room temperature in good yields (>90%) using anhydrous methanol or ethanol as solvents. On the other hand, only pyrido[2,3‐b]pyrazin‐3(4H)‐one (5a) was regioselectively attained in aqueous buffer of pH 7 while 3‐methylpyridopyrazinone derivatives were regioselectively separated using anhydrous methanol for one isomer, 5b, and anhydrous chloroform for the other isomer, 6b, at room temperature. Yields were higher than 80%. Reactions with benzoylformic acid did not give good yields and only 2‐phenylpyrido[2,3‐b]pyrazin‐3(4H)‐one (5c) could be obtained using anhydrous chloroform (yield <30%) as the solvent. Steric hindrance exerted by the phenyl group of the benzoylformic acid is supposed to be responsible of our difficulties to obtain 2‐phenylpyrido[2,3‐b]pyrazin‐3(4H)‐one (5c) in good yields applying this technique. The other isomer, 3‐phenyl[2,3‐b]pyrazin‐2(1H)‐one (6c) was always formed together with the former isomer and could not be isolated from the mixture, when other solvents than chloroform were used as the reaction media.
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