State a detailed mechanism for the electrophilic addition of HBr to 1-butene using the usual conventions. Explain the observed regiochemistry as well as stereochemistry and state whether the reactant(s) and product(s) are chiral and if they are optically active. Your mechanism and explanations should be sufficiently clear as well as complete that a reader is left with no doubt that you understand the chemical basis for these observations. Avoid simple decrees.