Photolysis of 1-alkylcycloalkanols in the presence of (diacetoxyiodo)benzene and I-2. Intramolecular selectivity in the beta-scission reactions of the intermediate 1-alkylcycloalkoxyl radicals

The C-C beta-scission reactions of 1-alkylcycloalkoxyl radicals, generated photochemically by visible light irradiation of CH2Cl2 solutions containing the parent 1-alkylcycloalkanols, (diacetoxy)-iodobenzene (DIB), and I-2, have been investigated through the analysis of the reaction products. The 1-alkylcycloalkoxyl radicals undergo competition between ring opening and C-alkyl bond cleavage as a function of ring size and of the nature of the alkyl substituent. With the 1-propylcycloheptoxyl, 1-propylcyclooctoxyl and 1-phenylcyclooctoxyl radicals, formation of products deriving from an intramolecular 1,5-hydrogen atom abstraction reaction from the cycloalkane ring has also been observed. The results are discussed in terms of release of ring strain associated to ring opening, stability of the alkyl radical formed by C-alkyl cleavage, and with cycloheptoxyl and cyclooctoxyl radicals, also in terms of the possibility of achieving a favorable geometry for intramolecular hydrogen atom abstraction

Early stages in the TiO2-photocatalyzed degradation of simple phenolic and non-phenolic lignin model compounds

The TiO2-photocatalyzed degradation of phenolic and non-phenolic benzyl alcohols, which can be considered simple lignin model compounds has been studied in aqueous solution under a variety of conditions, with the aim of acquiring fundamental information on the early stages of the degradation process. The role of the electron scavengers O-2, K2S2O8 and N2O on the degradation process as well as the influence of pH have been investigated. A major role in the degradation process is played by (OH)-O-. and O-2(.-), while SO4.- plays a minor role. (OH)-O-. plays a fundamental role in the conversion of non-phenolic substrates into phenolic ones, while O-2(.-) exerts its role mainly by reacting with phenoxyl radicals to give aromatic ring-opening products. Addition of K2S2O8 as electron scavenger allows substantial substrate degradation also in the absence of O-2, while N2O which is an excellent scavenger for the hydrated electron seems to be a very poor electron scavenger under the heterogeneous conditions employed. A general mechanistic scheme which proceeds through the formation of aromatic radical cations via one-electron oxidation of the neutral substrates by TiO2 (h(+)), accounting for all the experimental observations has been proposed. (C) 2004 Elsevier B.V. All rights reserved

The effect of ring substitution on the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals. A product and time-resolved kinetic study

A product and time-resolved kinetic study of the effect of ring substitution on the reactivity of 1,1-diarylalkoxyl radicals has been carried out. The radicals undergo an O-neophyl shift to give the isomeric 1-aryl-1-aryloxyalkyl radicals from which the corresponding aromatic ketones are formed. The rearrangement rate constants are influenced by ring substitution, increasing in the presence of electron-withdrawing substituents and decreasing in the presence of electron-donating ones. From the results of product and kinetic studies, the following migratory aptitudes have been obtained: 4-trifluoromethylphenyl; phenyl; 4-methylphenyl ; 4-methoxyphenyl. Excellent Hammett-type correlations between the sigma(+) substituent constants and both the visible absorption band maxima and the rearrangement rate constants have been obtained. The experimental results indicate that the rearrangement is governed by electronic effects in the starting 1,1-diarylalkoxyl radicals, whereas the stability of the rearranged carbon-centered radical plays a minor role, in line with a reactant-like transition state, strongly supporting the hypothesis that the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals proceeds through a concerted mechanism

Programa educativo sobre sexualidade e DST: relato de experiência com grupo de adolescentes Programa educativo sobre la sexualidad y Enfermedades Sexualmente Transmisibles: relacto de experiencia con un grupo de adolescentes Educative program about sexuality and Sexually Transmitted Diseases: experience report with a group of adolescents

O objetivo deste estudo foi relatar a experiência com grupo de adolescentes através de oficinas vivenciais sobre educação sexual. Realizamos 10 oficinas com adolescentes de baixa renda do Município de Aparecida de Goiânia/GO, que aconteceram a partir de reflexões e socialização do conhecimento sobre esta temática. O trabalho foi embasado na metodologia participativa de Paulo Freire e potencializado pela atenção dos coordenadores ao movimento do grupo, considerando suas necessidades e possibilidades. Concluímos que para o sucesso do trabalho interativo o coordenador de grupos deve ter uma escuta sensível aos anseios do grupo, especialmente o de adolescente. É necessário estimular a participação para a aquisição de conhecimentos o que favorecerá o exercício da cidadania e transformação da sua realidade social.<br>El objetivo de este estudio fue relatar la experiencia con grupo de adolescentes a través de talleres vivenciales sobre educación sexual. Realizamos 10 talleres con adolescentes de bajo poder adquisitivo del Municipio de Aparecida de Goiânia-GO, que se dieron a partir de reflexiones y socialización del conocimiento sobre esta temática. El trabajo fue realizado en base a la metodología participativa de Paulo Freire y potenciado por la atención de los coordinadores del movimiento del grupo, considerando sus necesidades y posibilidades. Concluimos que para el éxito del trabajo interactivo el coordinador de grupos debe tener una escucha sensible a los anhelos del grupo, especialmente de los adolescentes. Es necessário estimular la participación para la adquisición de nuevos conocimientos favoreciendo así el ejercicio de la ciudadanía para transformación de su realidad social.<br>The object of this study was to give an account of the experiment with a teenage group by using sexual education experiences of their own. Ten workshops were made with low-income teenagers of Município de Aparecida de Goiânia /GO, which happened because of the socialization and reflections about the contents of this study. The work was based on Paulo Freire's Participative Methodology and made better by the attention of the coordinators to every single group, considering their special needs and possibilities. We conclude that for the success of this work, the coordinator must listen to the group with a very sensitive prospect, especially when dealing with a teenage group. It is necessary to stimulate the participation, so that more can be learnt and the citizen work can be able to change its social reality