Hydroformylation is the transformation of an alkene to an aldehyde via the addition of both hydrogen and carbon monoxide. The final aldehyde has one more carbon atom than the precursor alkene. Two isomeric products can result. The regiochemistry of the hydroformylation reaction is believed to be controlled by the olefin insertion step. A reaction mechanism is usually studied by finding the reactants, products, intermediates, and transition states. Alternatively, a chemical reaction can be studied from the redistribution of the electron density along the reaction path connecting the stationary points. The aim of this work is to describe the reaction mechanism of the insertion process by the structural evolution defined by the changes in the electron density during the reaction.