When are you forbidden from making a Brocha Rishona on a food item,and obligated to make a Bracha Achrona after eating it?
The earlier answers may be right but not what i was looking for.
The Mishna Berurah in Siman 196 s”k 4 says that if you steal wheat and grind it into flour, although he is required to return it. Hallachicly he is its new owner, nevertheless he may not, make a brocha on food produced from that stolen wheat.The reason for this is based in the concept of “Ein zeh Mevareich elah menaeitz”(he’s not blessing, rather he is being disgusting). This concept is only true for Brocha Rishona; as far as the Bracha achrona is concerned, if one made bread out of stolen wheat and ate to the point of satiation, since he’s now obligated from the Torah to say Birkas Hamazon, he is not absolved of his obligation, and he still has too ‘bentch’.