969 resultados para [3 4] cycloaddition


Relevância:

100.00% 100.00%

Publicador:

Resumo:

The work described in this thesis has been divided into seven sections. The first section involves the preparation of N'-acyl-N'-arylN- benzothiohydrazides by the acylation of N'-aryl-N-benzothiohydrazides and is followed by a brief discussion of their possible conformation in solution. The second section deals with the preparation of 1,3,4-thiadiazolium salts by the action of perchloric acid/acetic anhydride on N'-acylN'- aryl-N-benzothiohydrazides and also by the reaction of N'-arylN- benzothiohydrazides with nitriles in an acidic medium. The preparation of 2-methylthio-I,3,4-thiadiazolium methosulfate by methylating the corresponding thione is also described. The third section deals with the reaction of 2-phenyl- and 2-methyl-I,3,4-thiadiazolium salts with alcohols in the presence of base. The stability and spectra of these compounds are discussed. Treatment of the 2-methyl-I,3,4-thiadiazolium salt with base was found to give rise to a dimeric anhydrobase and evidence supporting its structure is given. The anhydrobase could be trapped by a variety of acylating and thioacylating agents before dimerization occurred. In the fourth section, the reaction of N'-acyl-N'-aryl-N-benzothiohydrazides with a variety of acid anhydrides is described. These compounds were found to be identical with those obtained by acylating the anhydrobase. The mass spectral fragmentation of these compounds is described and the anomolous product obtained upon thiobenzoylation of 3-methyl-l-phenyl-pyrazal-5-one is also discussed. The fifth section deals with thioacyl derivatives of the anhydrobase which were prepared by the action of phosphorus pentasulfide upon the oxygen analogues and also obtained as the major product of the reaction of thioacetic acid with compounds related to N'-aryl-N-benzothiohydrazides. The mass spectra and p.m.r. spectra of these compounds are discussed. In the sixth section, the reaction of the 2-methylthio-l,3,4- thiadiazolium salt with active methylene compounds to give acyl and diacyl derivatives of the anhydrobase is described. Some aspects of these compounds are discussed. The seventh section describes the synthesis of ncyanine~' type dyes incorporating the l,3,4-thiadiazole ring and their spectra are briefly discussed.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The work herein has been divided into five sections. In the first section, a new method of converting N-aroyl- hydrazines to hydrazidic halides is described. The second section deals with the products of reaction of hydrazidic halides with thioacetate ion in acetonitrile at room temperature. A number of new acetylthiohydrazides has been isolated together with corresponding hyclrazidic sulphides. Examination of x-ray data for bis-[~ -(2,6- dibromophenylhydrazono) - benZYl] sulphide revealpd the symmetrical structure as the most probable. In the third section, which consists of the three subsections, the synthesis of the 4H-l,3,4 benzothiadiazine ring system has been extended to 4H-l,3,4 benzothiadiazines with substituents in the 5 and 6-positions. Extension of synthesis also involves 4H-l,3,4 benzothiadiazines with mora than one substituent. Nuclear magnetic resonance spectra of 5 and 6 substituted 4H-l,3,4 benzothiadiazines have been ,. recorded. The section ends with a discussion of the mass spectra of some 4H-l.3,4 benzothiadiazines. In the fourth section, which is divided into two sub- -sections, preparation of 7-nitro substituted 4H-l,3,4 benzothiadiazine from N-thiobenzoyl hydrazine and2,4-dinitro -fluorobenzene is found to be satisfactory. Thiohydrazides react with acetic anhydride, in some cases, to give products identical with acetylthiohydrazides obtained from the hydrazidic halides with thioacetate ion at room temperature. In most of the cases thiohydrazides are found to give anomalous products on reaction with acetic anhydride and mechanisms for their formation are discussed. In the fifth section, which forms three subsections, the 4H-l,3,4 benzothiadiazine ring system with a halogen substituent in the 7-position undergoes electrophilic attack preferentially in 5-posi tion. \fuen the 5-posi tion is occupied by a halogen atom, electrophilic substitution occurs at the 7-position of 4H-l,3,4 benzothiadiazine ring system. Substitution at the 4-nitrogen atom in 4H w l,3,4 benzo- -thiadiazine is extremely slow, probably due to delocalisa- -tion of the nitrogen lone pair in the system. Oxidation of 4H-l,3,4 benzothiadiazines occurs at the sulphur atom under relatively mild conditions. t The Appendix deals with the reaction of N-benzoyl-N - -(2,5-dibromophenyl)hydrazine with p-nitrothiophenol~ The proposed p-nitrothiophenoxy - intermediate may undergo benzothiadiazine formation in a proton exchange system.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Tesis (Maestría en Ciencias con Especialidad en Química Orgánica) UANL

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Tesis (Maestría en Ciencias Químicas, con especialidad en Química Orgánica) U.A.N.L.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Tesis (Maestría en Ciencias con orientación en Química Analítica Ambiental) UANL, 2014.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Poly(6-tert-butyl-3,4-dihydro-2H-1,3-benzoxazine) was synthesized by thermally activated cationic ring opening polymerization. The structure of the polymer was confirmed by spectral and thermal studies. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were estimated using cyclic voltammetry and optical absorption. Modulated photocurrent measurement technique was employed to study the spectral and field dependence of photocurrent. Photocurrent of the order of 1.5 micro A/m2 was obtained for polymer at a biasing electric field of 40 V/mico m.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Colección de cinco tebeos que sirve de material de apoyo para el tratamiento de la prevención de accidentes infantiles en la escuela. Este documento está integrado en los documentos de apoyo al desarrollo de la Educación para la Salud. El objetivo es que los alumnos tengan útiles necesarios para adquirir estilos de vida sanos y responsables acerca de su salud y la de los demás. El carácter lúdico que se plantea con estos tebeos, facilita el desarrollo de los temas de prevención desde una perspectiva personal, teniendo en cuenta los niveles de maduración del alumno. Los títulos que componen esta serie giran en torno a una familia (Martín Castaño), con los contenidos siguientes: las caídas, las quemaduras, la carga del trabajo, los productos tóxicos y los riesgos eléctricos.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Abordar el nacimiento y desarrollo de los primeros trazados del niño, habitualmente conocidos como garabatos, dentro de los cuales es posible discernir aquellos que configurarán un lenguaje gráfico básico de comunicación, que se manifestará en los primeros dibujos infantiles y en la escritura, dentro del trazado de las letras manuscritas, tanto mayúsculas como minúsculas. Los sujetos de la investigación son niños y niñas del tramo de Educación Infantil, con edades medias de 3, 4 y 5 años. Su número por curso oscilaba entre 24-25. Las pruebas se agrupan en cinco grandes bloques: 1.- Grafismos 2.- Relaciones geométricas 3.- Relación garabato-escritura 4.-Dibujo 5.- Escritura. A lo largo de los dos años se realizan 25 pruebas con 79 aplicaciones y con un total de 1.715 láminas realizadas por los niños: 15 de ellas con criterios de tipo cuantitativo-estadístico y 10 con un enfoque de corte eminentemente cualitativo. El amplio número de pruebas responde, por un lado, a la necesidad de variar las actividades ante los niños de edades pequeñas y, por otro, a la de alcanzar con cierto rigor conclusiones que estén suficientemente fundamentadas tanto cualitativa como cuantitativamente. Las conclusiones responden a los tres bloques de los objetivos planteados como respuesta final a las interrogantes que han marcado este trabajo 1.- Grafismos 2.- Dibujo 3.- Escritura. Se llega a sólidas conclusiones referidas tanto a los aspectos psicomotores en la gestación de los garabatos, como en las formas de representación de los dibujos y de la escritura, sistemas expresivos y comunicativos fuertemente entrelazados en los inicios del aprendizaje infantil.