In chemistry, regioselectivity's the preference of one direction of chemical bond making or breaking over all other possible directions . It can often apply to which of many possible positions a reagent will affect, such as which proton a strong base will abstract from an organic molecule, or where on a substituted benzene ring a further substituent will add. A specific example's a halohydrin formation reaction with 2-propenylbenzene : » The reaction product's a mixture of two isomers and the r… (More on Regioselectivity)