10. A reaction mechanism describes the sequence of steps occurring during a reaction. Gaining an intuitive understanding of reaction mechanisms allows the accurate prediction of products for new reactions, a key goal of any organic chemistry course. Most mechanisms involve combinations of the four elementary steps described as: 1) Make a bond, 2) Break a bond, 3) Add a proton or 4) Take a proton away. Learning how to predict which of these four, or perhaps some other less common elementary step, is appropriate at a given stage in a mechanism requires recognition of the properties of the participating molecules. When writing mechanisms, arrows are used to indicate the redistribution of electrons during each step.