I am new to LaTeX and intend to use it to create articles in the field of chemistry. Which immediately brings me to my question. Suppose I want to include these two images (which I just googled):

I would off cource like all the rings to be off the same size. Is there a smart way to do this? I use ChemDraw and export as .eps.
The only thing I could come up with is to use the ratio between the picture of the smallest molecule and the largest molecule as the scaling factor but I am unable to find how to retrieve the size of a picture.
Any help is appreciated.
Martin