Pure anhydrous caffeine is a white colorless powder with a melting point of 227° C to 228° C. Caffeine is moderately soluble in water at room temperature (2 g/100mL), but very soluble in boiling water (66 g/100mL). It is also moderately soluble in ethanol (1.5 g/100mL).
Caffeine is an achiral molecule without stereoisomers.
There are two amide groups of caffeine. They exist predominately as zwitterionic resonance structures where the nitrogen and carbon atoms are double bonded to each other so that both nitrogen atoms are essentially planar (in sp2 orbital hybridization).
Common sources of caffeine are coffee, tea, soft drinks and energy drinks, and (to a lesser extent) chocolate derived from cocoa beans.
Tea contains more caffeine than coffee by dry weight. A typical serving, however, contains much less, since tea is normally brewed much weaker.
One of the world’s primary sources of caffeine is the coffee “bean” (which is the seed of the coffee plant), from which coffee is brewed.
Tea contains more caffeine than coffee by dry weight. A typical serving, however, contains much less, since tea is normally brewed much weaker. Also contributing to caffeine content are growing conditions, processing techniques, and other variables. Thus, certain types of tea may contain somewhat more caffeine than other teas.
Caffeine is also a common ingredient of soft drinks, such as cola, originally prepared from kola nuts. It is also the operative ingredient in energy drinks, which offer 80 milligrams of caffeine per serving, whereas soft drinks contain 10 to 50 milligrams.
Various manufacturers market caffeine tablets, claiming that using caffeine of pharmaceutical quality improves mental alertness. These effects have been born out of research that shows caffeine use results in decreased fatigue and increased attentiveness.