[brasarehot]

If you're given a complex molecule, Ex: GTP, how do you calculate how many possible resonance structures exist before attempting to draw them all? I was just wondering if this was possible so I could make sure I draw ALL possible forms and I didn't leave any out.

[fledarmus]

It isn't the size or complexity that determines how many resonance structures you can come up with, it is the functionalities present in the molecule.

You just need to get familiar with structures that have resonance structures and learn to recognize them in the molecule. Like chess - don't memorize all the moves in a game, learn to recognize the patterns and apply them to whatever position you are in.