Knowing what the products are in the reaction between hydroxide and HBr, we can make our first attempt at using curved arrows to show a mechanism that takes account of which bonds are formed and broken. This general idea will be used extensively throughout the Organic sequence. The electron-rich hydroxide base is attracted to the electron-poor proton on H-Br (H EN = 2.1; Br = 2.8) so they interact to begin forming a bond. Since we know only one bond needs to form and one needs to break, we can be sure this won’t be a complicated mechanism. In fact, everything can happen at once in a concerted process, which is confirmed by kinetic data, that shows the reaction to be bimolecular. Two curved arrows only will be needed here to give the reaction mechanism.