Vol. 119 No. 3 (2023)

A summary of some methods used in the synthesis of bioactive natural products of marine origin is presented. The article is structured according to the order in which the most important bonds in the oxygenated heterocycles are introduced. The similarity of some synthetic methods used with those used by living organism producers is also discussed.

Keywords: Enantioselective synthesis, natural products, cyclic ethers, stereochemistry, metals, catalysis

The design of ordered porous architectures as heterogeneous catalysts for sustainable organic transformations is an interdisciplinary research area in the frontier between catalysis and nanomaterials. On the one hand, this review presents different families of ordered porous architectures, such as silicates, mesoporous silicas, and metal-organic frameworks, describing examples of geometries and compositions. On the other hand, its catalytic behavior is exemplified in the transformation of organic molecules by multi-step (C-C, C-O, and C-N bond formations) organic synthesis of high-added value oxo- and aza-compounds of interest in fine chemistry and pharma industries.

Keywords: Heterogeneous catalysis, porous solids, metal-organic frameworks, organic synthesis, green chemistry

Nowadays, photoredox catalysis is an essential tool to synthesize high-value compounds as it enables the activation of those compounds that were traditionally inaccessible. More specifically, photoredox catalysis has emerged as a major supplier for carbon centred radicals, which are increasingly necessary to meet the most demanding synthetic challenges in organic chemistry. In addition, computational chemistry has become a crucial tool to understand and develop this chemistry. Particularly, Density Functional Theory (DFT) has been widely used for this purpose. Herein, we describe four mechanistic studies based on photoredox catalysis analyzed by means of DFT, showing the importance of these techniques that are at the forefront of photoredox chemistry.

Keywords: Halogen Atom Transfer, Hydrogen Atom Transfer, Carbon centred radicals, Photoredox Catalysis, Density Functional Theory (DFT)

University entrance exams (known in Spain as PAU) exert a proven influence on the way of teaching the different subjects in upper secondary education. This article presents some questions taken from chemistry exams proposed in the PAU that follow a competence approach adjusted to the requirements of the LOMLOE. The inclusion of questions of this type is considered a necessary condition, although not sufficient, to make aspects such as experimental work, chemistry applications and STEM learning, more relevant in the classroom.

Keywords: Assessment, chemistry teaching, competencies, STEM learning, university entrance exams

The rising of water inside an inverted vessel that contains a burning candle is a typical recreational experiment whose result is well known. Water ascends due to a pressure reduction inside the vessel, but the contribution of different (physical and chemical) processes to this explanation is still under debate. In this work we present a quantitative detailed discussion of the main processes involved in this experiment, concluding that the major contribution to the pressure decreasing causing the rise of the water level in the inverted vessel is due to the hot air escaping from its interior (~ 20% pressure reduction), whereas the consumption of oxygen in the chemical reaction has only a minor role (7% as a maximum). This result is practically independent of the vessel volume, the ambient temperature and, for practical purposes, the type of paraffin with which the candle is made.

Keywords: Vessel on a candle, Air escape, Combustion of paraffin, Fraction of oxygen consumed by a candle