# Question #019dd

As you can see, steam typically reacts with alkenes by adding $H$ on one double-bonded atom and $O H$ on the other. But there are two possible choices for which atom gets the single hydrogen atom and which gets the $O H$ group. In some cases like (A) there is a perference (the Markovnikov rule), but the only sure way to get 100% of one product is to have the double bond in the middle of the molecule so that the two possible molecules are the same by symmetry. (C) does that.