#"Regioselectivity"# refers to the preference of a chemical reaction to proceed in ONE direction as opposed to another. Consider a simple reaction...the hydrohalogenation of propylene by #HX#...for which TWO products are possible, and are observed...
#"H"_3"CCH=CH"_2 + "HX" rarr "H"_3"CCHXCH"_3+ "H"_3"CCH"_2"CH"_2"X"#
MORE of the secondary alkyl halide is obtained....
This major product is the so-called #"Markownikow product"#, and the reaction proceeds in this direction of the basis of the enhanced stability of #2^@# carbocation...#H_3C-stackrel(+)CH-CH_3# versus the primary carbocation...#H_3C-CH_2-stackrel(+)CH_2#
If there is a specific issue or observation, please refine the question... As for any physical or chemical phenomenon, you do the experiment FIRST, and then try to interpret it.
