How do I know how many isomers to draw for a molecular formula? My professor said there was a formula, but he did not know it off the top of his head. He said to google it, but I CANNOT find a formula, and I have about 12 opened windows with diff. searches *rolls eyes*. Ex. I know C3H5F2Br has 9 isomers. But how would I know it had that many (9)? And is there a way to draw these better? I am getting about 2/3 of the isomers, and my professor says he wishes there was a way he could explain it, but he can't. All he said was, no flipping and no rotating isomers bc they are the same thing. But Why are there no set ways to do this? *sadness* :( Any advice, I greatly appreciate. Fridays/saturdays I spend doing homework.