to the OP..the alpha proton (one on the carbon next to the carbonyl) is the most acidic proton. This proton is replaced with a Cl, Br, or whatever halogen. If it is an acid..it adds once (unless xs is used). If it's Br2 and OH- you should expect multiple halogens on the neighboring alpha carbons.
You were thinking of an aromatic ring. That's when those rules apply. For A.rings you would do, Br2 and FeBr3 (or any lewis acid) and you would get the meta electrophilic substitution. This is aromatic rings only. So the 4n+2 rule applies.