Caffeine is a member of the class of compounds
organic chemists call alkaloids. Alkaloids are nitrogencontaining
basic compounds that are found in plants. They
usually taste bitter and often are physiologically active in
humans. The names of some of these compounds are
familiar to you even if the structures aren’t: nicotine,
morphine, strychnine, and cocaine. The role or roles these
compounds play in the life of the plants in which they are
found is not well understood. In some cases they may act as
pesticides; nicotine is found in tobacco and has been sprayed
onto other plants, in which it is not found, to function as an
insecticide. The structure of caffeine is shown to the right. It
can be considered to be constructed from the purine ring
system, which is important biologically, being found in
nucleic acids and elsewhere.