Synthesis of dimethyl acetal of ketones: design of solid acid catalysts for one-pot acetalization reaction

The synthesis of dimethyl acetals of carbonyl compounds such as cyclohexanone, acetophenone, and benzophenone has successfully been carried out by the reaction between ketones and methanol using different solid acid catalysts. The strong influence of the textural properties of the catalysts such as acid amount and adsorption properties (surface area and pore volume) determine the catalytic activity. The molecular size of the reactants and products determine the acetalization ability of a particular ketone. The hydrophobicity of the various rare earth exchanged Mg–Y zeolites, K-10 montmorillonite clay, and cerium exchanged montmorillonite (which shows maximum activity) is more determinant than the number of active sites present on the catalyst. The optimum number of acidic sites as well as dehydrating ability of Ce3+-montmorillonite and K-10 montmorillonite clays and various rare earth exchanged Mg–Y zeolites seem to work well in shifting the equilibrium to the product side.

Studies on the Solvent Dependence in the Reaction of a Few (Anthracen-9-yl)MethyLamines and Sulfanes with Reactive Acetylenes

The thesis entitled ‘Studies on the Solvent Dependence in the Reaction of a Few (Anthracen-9-yl)methylamines and Sulfanes with Reactive Acetylenes’ is divided into six chapters. ln Chapter l a general survey of electron transfer reactions, Diels-Alder reactions and Michael-type additions is presented. A detailed discussion on the synthesis of several (anthracen-9-yl)methylamines is presented in Chapter 2. In Chapter 3, results of preliminary photophysical studies on a few (anthracen-9yl) methylamines are compiled. A detailed discussion on extensive examination of dependence in the reaction of (anthracen-9-yl)methylamines with reactive acetylenes is presented Chapter 4. Details on the synthesis and reaction of a few (anthracen-9-yl)methylsulfanes with DMAD are described in Chapter 5.

Studies on nonlinear dynamics of certain reaction systems

The nonlinear dynamics of certain important reaction systems are discussed and analysed in this thesis. The interest in the theoretical and the experimental studies of chemical reactions showing oscillatory dynamics and associated properties is increasing very rapidly. An attempt is made to study some nonlinear phenomena exhibited by the well known chemical oscillator, the BelousovZhabotinskii reaction whose mathematical properties are much in common with the properties of biological oscillators. While extremely complex, this reaction is still much simpler than biological systems at least from the modelling point of view. A suitable model [19] for the system is analysed and the researcher has studied the limit cycle behaviour of the system, for different values of the stoichiometric parameter f, by keeping the value of the reaction rate (k6) fixed at k6 = l. The more complicated three-variable model is stiff in nature.

Pulsed-field studies of the magnetization reversal in molecular nanomagnets

We report experimental studies of crystals of Mn12 molecular magnetic clusters in pulsed magnetic fields with sweep rates up to 410^3 T/s . The steps in the magnetization curve are observed at fields that are shifted with respect to the resonant field values. The shift systematically increases as the rate of the field sweep goes up. These data are consistent with the theory of the collective dipolar relaxation in molecular magnets.

Ground and Excited State Electron Transfer Reaction Between a few Anthracene Appended Tertiary Amines and Suitable Electron Acceptors

the thesis entitled “Ground and Excited State Electron Transfer Reaction Between a few Anthracene Appended Tertiary Amines and Suitable Electron Acceptors” portrays our attempts to explore the solvent, concentration and temperature effect of the reaction between a few (anthracen-9- yl)methanamines with electron acceptors like DMAD, DBA and DBE. We have also studied the effect of solvent and percentage fluorescence quenching in the photoinduced electron transfer reactions of these ‘donor-spacer-acceptor’ systems. Finally we look in to the intramolecular electron transfer reactions of a few tertiary amine appended dibenzobarrelenes and bisdibenzobarrelenes

Novel [3+2] annulation reaction of nitrones with Burgess reagent and a few related reactions

Burgess reagent first prepared by E. M. Burgess in 1968, is a mild and selective dehydrating agent for secondary and tertiary alcohols and due to the amphipolar nature it is gainfully employed in a number of creative synthetic ventures. A close examination of the structure of Burgess reagent reveals that it can act as a 1,2-dipole. To the best of our knowledge, no attempts have been made to tap full synthetic potential of the amphipolar nature of this reagent and no reports on 1,3-dipolar addition to a σ-bond in acyclic systems are available in literature. In this context, we propose to unravel novel applications of Burgess reagent based on its amphipolar nature. Rich and multifaceted chemistry of nitrones form the basis of many successful chemical transformations used in attractive synthetic strategies. For the last 50 years special attention has been given to nitrones due to their successful application as building blocks in the synthesis of various natural and biologically active compounds. Our interest in nitrones stems out of its unique character: i.e. it is a 1,3-dipole exhibiting distinct nucleophilic activity. We reasoned that 1,3-dipole possessing significant nucleophilicity should react with amphipolar Burgess reagent with elimination of triethylamine to give the corresponding five-membered ring product by formal dipolar addition to a σ bond. To test this hypothesis we studied the reaction of nitrones with Burgess reagent. This thesis reveals our attempts to explore the [3+2] annulation reaction of nitrones with Burgess reagent which was found to be followed by a rearrangementinvolving C-to-N aryl migration, ultimately resulting in diarylamines and carbamates. We have also examined the reaction of cyanuric chloride with nitrones in DMF with a view to exploit the nucleophilicty of nitrones and to unravel the migratory aptitude, if any, observed in this reaction

Semi-algebraic methods for symbolic analysis of complex reaction networks

The identification of chemical mechanism that can exhibit oscillatory phenomena in reaction networks are currently of intense interest. In particular, the parametric question of the existence of Hopf bifurcations has gained increasing popularity due to its relation to the oscillatory behavior around the fixed points. However, the detection of oscillations in high-dimensional systems and systems with constraints by the available symbolic methods has proven to be difficult. The development of new efficient methods are therefore required to tackle the complexity caused by the high-dimensionality and non-linearity of these systems. In this thesis, we mainly present efficient algorithmic methods to detect Hopf bifurcation fixed points in (bio)-chemical reaction networks with symbolic rate constants, thereby yielding information about their oscillatory behavior of the networks. The methods use the representations of the systems on convex coordinates that arise from stoichiometric network analysis. One of the methods called HoCoQ reduces the problem of determining the existence of Hopf bifurcation fixed points to a first-order formula over the ordered field of the reals that can then be solved using computational-logic packages. The second method called HoCaT uses ideas from tropical geometry to formulate a more efficient method that is incomplete in theory but worked very well for the attempted high-dimensional models involving more than 20 chemical species. The instability of reaction networks may lead to the oscillatory behaviour. Therefore, we investigate some criterions for their stability using convex coordinates and quantifier elimination techniques. We also study Muldowney's extension of the classical Bendixson-Dulac criterion for excluding periodic orbits to higher dimensions for polynomial vector fields and we discuss the use of simple conservation constraints and the use of parametric constraints for describing simple convex polytopes on which periodic orbits can be excluded by Muldowney's criteria. All developed algorithms have been integrated into a common software framework called PoCaB (platform to explore bio- chemical reaction networks by algebraic methods) allowing for automated computation workflows from the problem descriptions. PoCaB also contains a database for the algebraic entities computed from the models of chemical reaction networks.

Generalization over contrast and mirror reversal, but not figure-ground reversal, in an "edge-based

Baylis & Driver (Nature Neuroscience, 2001) have recently presented data on the response of neurons in macaque inferotemporal cortex (IT) to various stimulus transformations. They report that neurons can generalize over contrast and mirror reversal, but not over figure-ground reversal. This finding is taken to demonstrate that ``the selectivity of IT neurons is not determined simply by the distinctive contours in a display, contrary to simple edge-based models of shape recognition'', citing our recently presented model of object recognition in cortex (Riesenhuber & Poggio, Nature Neuroscience, 1999). In this memo, I show that the main effects of the experiment can be obtained by performing the appropriate simulations in our simple feedforward model. This suggests for IT cell tuning that the possible contributions of explicit edge assignment processes postulated in (Baylis & Driver, 2001) might be smaller than expected.

The Kineticist's Workbench: Combining Symbolic and Numerical Methods in the Simulation of Chemical Reaction Mechanisms

The Kineticist's Workbench is a program that simulates chemical reaction mechanisms by predicting, generating, and interpreting numerical data. Prior to simulation, it analyzes a given mechanism to predict that mechanism's behavior; it then simulates the mechanism numerically; and afterward, it interprets and summarizes the data it has generated. In performing these tasks, the Workbench uses a variety of techniques: graph- theoretic algorithms (for analyzing mechanisms), traditional numerical simulation methods, and algorithms that examine simulation results and reinterpret them in qualitative terms. The Workbench thus serves as a prototype for a new class of scientific computational tools---tools that provide symbiotic collaborations between qualitative and quantitative methods.

Estudio sobre indicadores de validez del Reversal Test.

Comprobar la siguiente hipótesis: si ciertamente el Reversal es un test de madurez, sus resultados pueden constituir un índice predictivo del rendimiento en otras áreas. 740 alumnos de primero de EGB de centros de la región asturiana a través de un procedimiento aleatorio por conjuntos. La población se estratificó según: sexo, hábitat, régimen de enseñanza y asistencia o no de los alumnos a centros preescolares en el curso anterior. Para comprobar la hipótesis planteada, se relacionan los datos obtenidos en este test con los resultados de aquellos otros indicadores del rendimiento de los alumnos de primero de EGB: evaluación o exploración inicial de los alumnos efectuada por el docente al comenzar primero de EGB, los resultados del test de aptitudes cognoscitivas primaria I, y finalmente, la evaluación final al terminar el nivel de primero. Cuestionario 'ad hoc' con respuestas cerradas en escala y paramétrica, destinado a los docentes. Reversal y Test de aptitudes cognoscitivas primaria I. Calificación final en el área de Matemáticas, Lenguaje y global y calificaciones obtenidas por los alumnos en dos pruebas objetivas (Lenguaje y Matemáticas) expresamente preparadas con este fin. Análisis de las relaciones entre el reversal y las puntuaciones obtenidas en los demás indicadores. Cálculo de la validez de este test como instrumento predictivo a través de sus correlaciones con los demás indicadores utilizados.. Diferencias en función del nivel de maduración y el sexo: los alumnos clasificados con bajo nivel de maduración por el Reversal, obtienen las puntuaciones inferiores en todas las variables utilizadas; superioridad de las niñas respecto a los niños, aunque las diferencias no llegan a ser significativas. Interacción de variables en función del grado de madurez y el sexo: las correlaciones más elevadas se dan entre los índices de rendimiento y la madurez cognoscitiva evaluada por los docentes al comenzar el curso; se obtienen coeficientes diferentes con los diversos grupos entre rendimiento y test de aptitudes cognoscitivas, en los índices entre personalización y rendimiento se refleja claramente la influencia del nivel de maduración y el sexo. Relaciones entre el reversal y otros indicadores del rendimiento en función de la preescolarización: las correlaciones más altas se dan entre el Reversal y el Test de inteligencia primaria I; respecto al rendimiento de fin de curso los índices también son claramente representativos; los índices tienden a ser más bajos y desiguales en las relaciones entre el Reversal y la madurez cognoscitiva inicial evaluada por los docentes. Gran utilidad del Reversal como instrumento de diagnóstico y predicción. Se recomienda su utilización en los docentes por su facilidad de aplicación, valoración e interpretación. Este test permite obtener una información sobre el nivel de maduración del niño y 'pistas' de posibles anomalías o retrasos en las áreas perceptiva, espacial, etc..

Reaction times as a measure of uncertainty. 'Tiempo de reacci??n como una medida de incertidumbre'

Resumen tomado de la publicaci??n

El Reversal Test y la Ficha de Observaci??n de G. Yoakam en la determinaci??n de la madurez para la lectura

Resumen tomado de la publicaci??n