One of the biggest challenges in astrochemistry is to gain a better understanding of the chemical processes that take place in space. This could ultimately help to answer the question: What is the origin of life on Earth? This thesis has aimed to get an idea of the formation of polycyclic aromatic hydrocarbons in space. This has been done by envisioning that that gaining a better understanding of related earthlike processes will help to obtain a more complete picture of analogous processes within an astrochemical context. An example of a chemical reaction that is commonly used in laboratories to create six-membered ring motifs is the Diels-Alder reaction. This thesis is, therefore, dedicated to obtaining a better understanding of how different types of Lewis acids catalyze Diels-Alder reactions by using state-of-the-art quantum chemical techniques. The results obtained in this thesis completely contradict the traditional view of Lewis acid-catalyzed Diels-Alder reactions and thus present a paradigm shift in organic chemistry. In fact, it turns out that Lewis acid catalysts accelerate Diels-Alder reaction not by increasing the attraction between the reactants but rather by reducing the steric repulsion between them. These, and other finding emerging from this thesis, not only provide a more complete understanding of the formation of polycyclic aromatic hydrocarbons in space but also contribute to the development of more economically and environmentally sustainable Lewis acid-catalyzed Diels-Alder reactions.
