Does a Dark Roast Coffee have more caffeine then a Light Roast Coffee?

@meJess A chemistry graduate student once told me that the caffeine in tea and the caffeine in coffee are different stereoisomers. That is, the molecules have the same chemical formula but the atoms are arranged in one shape in tea and in another shape in coffee. The isomer is tea is not as readily absorbed by the body as the one in coffee.

I have some experience that verifies this. I dislike coffee and drink only tea. But years ago, someone offered me some "Irish coffee" -- coffee, Irish whiskey, and sweet cream. I had some at night -- the whiskey was so strong that i did not even taste the coffee! lol. But when I tried to get to sleep that night, I felt a buzz that kept me awake. On the other hand, I regularly drink black tea at night and have no problem falling asleep afterward.