Regeochemistry is basically the study of the different pathways that our two reactants can take. Now, in the reaction above, pathway one is more favorable, it's more likely to occur. And that's because this intermediate carbocation, this tertiary carbocation is more stable than this primary carbocation. And we'll examine that in a future lecture. So because pathway one is more favorable, it's more stable, it's more likely to take place. And generally, when a reaction can occur in several ways and one of the pathways predominates the reaction is called regioselective.