This article provides a comprehensive review of aliphatic nucleophilic substitution (SN1 and SN2) and elimination (E1 and E2) reactions. It delves into the fundamental mechanistic principles governing these transformations, including kinetics, stereochemistry, and the factors influencing reaction pathways. The interplay between substitution and elimination is explored, highlighting the roles of substrate structure, nucleophile/base strength, solvent effects, and temperature. Furthermore, this work examines recent advancements in computational chemistry and artificial intelligence (AI) that are revolutionizing our ability to predict and understand these complex reactions.

This report offers a critical and reflexive assessment of the application of gender as a category of historical analysis in Brazilian historiography, focusing on the Republican period from 1889 to 1989. The analysis demonstrates how gender analysis has enabled innovative reinterpretations of key processes in Brazilian history, incorporating critical perspectives on masculinities and intersectionality. The report concludes that citizenship definition, labour organisation, authoritarian projects, and struggles for democracy have been profoundly gendered processes.

This article provides a comprehensive review of addition reactions to carbon-carbon multiple bonds, a fundamental class of transformations in organic chemistry. We delve into the electronic structure of alkenes and alkynes, elucidating the inherent reactivity of the π-bond. The discussion encompasses a detailed examination of various addition reactions, including hydrohalogenation, hydration, halogenation, halohydrin formation, hydroboration-oxidation, and catalytic hydrogenation. We explore the principles of regioselectivity and stereochemistry, with a particular focus on Markovnikov's rule and anti-Markovnikov additions.

This report examines the historiography of social struggles in Republican Brazil from 1889 to 1989, analysing how different theoretical frameworks have shaped our understanding of labour movements, peasant resistance, and urban social mobilisation. The study traces the evolution from traditional labour history to more nuanced approaches incorporating gender, race, and everyday resistance, demonstrating how historiographical debates have reflected broader transformations in Brazilian society and academic discourse.

This article explores the fundamental principles of molecular evolution, examining how genetic material changes over time and drives biological diversity. The work integrates classical evolutionary theory with modern molecular biology, discussing mutation rates, natural selection at the molecular level, neutral theory, and the molecular clock hypothesis. The article provides insights into how DNA and protein sequences reveal evolutionary relationships and inform our understanding of life's history.