Answer to Question #84583 in Organic Chemistry for Amit patra

Question

b) With the help of examples explain the following terms:
i) Regioselectivity
ii) Stereoselectivity

Answer 1

i) Regioselectivity in organic chemistry refers to the favoring of a reagent to bond to one atom over another.

For example in the reaction of propene with hydrobromic acid (HBr), two possible products are possible, both of which are called regioisomers. It turns out, however, that only one of the products is formed as the major product and only trace amounts of the minor is observed (according to Markovnikov's rule):

Because of the preference for the formation of one product over another, the reaction is selective. This reaction is regioselective because it selectively generates one constitutional isomer rather than the other.

ii) When a reaction is said to be stereoselective it means that a single stereoisomer is formed even though more than one may be possible. Stereoisomers are compounds that have the same chemical formula and the same atom connectivity, but different three-dimensional orientations.