How many of the following alkenes on addition of HBr would give the same product in the presence or absence of peroxide? Propene, 1-butene, 2-butene, 3-hexene, 2,3-dimethyl-2-butene,  1,2-dimethyl cyclohexene, 1,4-dimethyl-2-cyclohexene, 3,4-dimethyl-3-hexene, cyclohexene.