I seem to have a problem with caffeine. I tend to experience a lot of the negative effects, like diuresis, extreme hunger suppression and paranoia, at two or three cups of coffee, while I don't experience the positive effects, like alertness and focus, without drinking as many as five or six cups. Are there chemicals with similar effects, but that aren't caffeine?
There is a substance similar to caffeine - theobromine, found in cocoa. They are chemically similar, and have some similar effects*:
the formula above shows theobromine,
and this is caffeine.
Of course, there is the concern if you react like you described to one xanthine derivative (caffeine), would you react in a similar way to another compound from this group. Also the atypical reaction to caffeine might be something you want to have checked further (i.e. consult a physician about it).
There are many chemicals (some found in various herbs) that have various sorts of stimulating effects on the central nervous system, but tampering with the CNS can be very dangerous, and indeed many of these substances have serious side effects, far more serious than caffeine.
An aside: depending on how alert one needs to be, a lemonade can be a quick home remedy: water will keep you hydrated (necessary for alertness), sugar (or honey) will keep your brain "fueled", vitamins will help your metabolic processes, and sour taste does have a short-term awakening effect. Of course, like with anything, moderation is the key.
*Various research papers show controversial results regarding the stimulating effects on theobromine (some show some effect, some don't, and some show opposite effects in certain doses). They mostly agree that the effects are weaker than in caffeine, dose dependent, and may depend on previous use of products containing caffeine and/or theobromine. (see ref 4, 5 and 6). Ref:
Dr. Duke's Phytochemical and Ethnobotanical Databases at United States Department of Agriculture
Formulae from Wikipedia
Hendrik J. Smit, Elizabeth A. Gaffan, Peter J. Roger: Methylxanthines are the psycho-pharmacologically active constituents of chocolate, Psychopharmacology, November 2004, Volume 176, Issue 3, pp 412-419
Geoffrey K. Mumford, Suzette M. Evans, Barbara J. Kaminski, Kenzie L. Preston, Christine A. Sannerud, Kenneth Silverman, Roland R. Griffiths: Discriminative stimulus and subjective effects of theobromine and caffeine in humans, Psychopharmacology, June 1994, Volume 115, Issue 1, pp 1-8
Matthew J. Baggott, Emma Childs, Amy B. Hart, Eveline de Bruin, Abraham A. Palmer, Joy E. Wilkinson, Harriet de Wit: Psychopharmacology of theobromine in healthy volunteers, Psychopharmacology DOI 10.1007/s00213-013-3021-0