Computational chemistry addresses chemical problems by modelling chemical processes through calculations, and has proven to be an excellent tool for conducting chemical research. This thesis focuses on the modelling of chemical reactions using density functional theory. These chemical reactions are divided into two categories: two reaction mechanisms in organometallic catalysis, and three different binding and/or mechanistic studies involving supramolecular cavitands. The calculations uncover mechanistic details and origins of selectivity which experiments alone could not have explained.

The first organometallic reaction studied concerns the dehydrogenation of amines with (cyclopentadienone)iron carbonyl. The results show a stepwise mechanism involving a rate-limiting hydride transfer followed by a much faster proton transfer. The calculations contribute to a more nuanced understanding of the reaction mechanism in general.  The second reaction studied is the gold-catalysed cycloisomerisation of acetylenic acids to lactones. A detailed mechanism of the cycloisomerisation reaction was calculated, and the origins of the observed regioselectivity and stereoselectivity were uncovered. The results show a strong favouring of a mechanism involving an anti-addition of the carboxylic acid to the alkyne moiety, yielding (Z)-exo-alkylidene γ-lactones in the case of substituted alkynes. 

The first reaction in a supramolecular cavitand considered here is the aforementioned cycloisomerisation of acetylenic acids, this time in a gold-functionalised resorcin[4]arene-based cavitand. The calculations give insights into the structure-activity relationship between the cavitand and several substituted alkyne-acids. Furthermore, the calculations show that the cavitand itself has a modest catalytic power. A binding study of several hydrophilic molecules in a resorcin[4]arene-based cavitand with pyridinyl-benzimidazole panels was conducted. It was found that the water molecules form a hydrogen-bonding network between the panels of the cavitand, as well as on the hydrophilic rim. These interactions explain the high binding affinity of hydrophilic molecules to a hydrophobic cavitand. Finally, the mechanism for the hydrolysis of acetylcholine in a similar resorcin[4]arene-based cavitand was investigated to discern possible catalytic applications. The calculations show that the hydrolysis reaction is associated with prohibitively high barriers inside of the cavitand, and hence the cavitand cannot catalyse this reaction.