1.3 Chemically speaking, what is caffeine?

Caffeine is an alkaloid. There are numerous compounds called alkaloids, among them we have the methylxanthines, with three distinguished compounds: caffeine, theophylline, and theobromine, found in cola nuts, coffee, tea, cacao beans, mate and other plants. These compounds have different biochemical effects, and are present in different ratios in the different plant sources. These compounds are very similar and differ only by the presence of methyl groups in two positions of the chemical structure. They are easily oxidized to uric acid and other methyluric acids which are also similar in chemical structure.

Sources: Coffee, tea, cola nuts, mate, guarana.
Effects: Stimulant of central nervous system, cardiac muscle, and respiratory system, diuretic Delays fatigue.

Sources: Tea
Effects: Cariac stimulant, smooth muscle relaxant, diuretic, vasodilator

Sources: Principle alkaloid of the cocoa bean (1.5-3%) Cola nuts and tea
Effects: Diuretic, smooth muscle relaxant, cardiac stimulant, vasodilator.

(Info from Merck Index)

The presence of the other alkaloids in colas and tea may explain why these sometimes have a stronger kick than coffee. Colas, which have lower caffeine contents than coffee are, reportedly, sometimes more active. Tea seems the strongest for some. Coffee seems more lasting for mental alertness and offers fewer jitters than the others.

A search in CAS and produced these names and synonyms:
N   58-08-2  REGISTRY
CN   1H-Purine-2,6-dione, 3,7-dihydro-1,3,7-trimethyl- (9CI)  (CA INDEX NAME)

CN   Caffeine (8CI)
CN   1,3,7-Trimethyl-2,6-dioxopurine
CN   1,3,7-Trimethylxanthine
CN   7-Methyltheophylline
CN   Alert-Pep
CN   Cafeina
CN   Caffein
CN   Cafipel
CN   Guaranine
CN   Koffein
CN   Mateina
CN   Methyltheobromine
CN   No-Doz
CN   Refresh'n
CN   Stim
CN   Thein
CN   Theine
CN   Tri-Aqua

MF   C8 H10 N4 O2

The correct name is the first one, 1H-Purine-2,6-dione, 3,7-dihydro-1,3,7-trimethyl- (This is the "inverted name") The "uninverted name" is 3,7-Dihydro-1,3,7-trimethyl-1H-purine-2,6-dione

Merck Index excerpt...

Caffeine: 3,7-dihydro- 1,3,7-trimethyl- 1H-purine- 2,6-dione; 1,3,7-trimethylxanthine; 1,3,7-trimethyl- 2,6-dioxopurine; coffeine; thein; guaranine; methyltheobromine; No-Doz.

C8H10N4O2; mol wt 194.19. C 49.48%, H 5.19%, N 28.85%, O 16.48%.

Occurs in tea, coffee, mate leaves; also in guarana paste and cola nuts: Shuman, U.S. pat. 2,508,545 (1950 to General Foods). Obtained as a by-product from the manuf of caffeine-free coffee: Barch, U.S. pat. 2,817,588 (1957 to Standard Brands); Nutting, U.S. pat. 2,802,739 (1957 to Hill Bros. Coffee); Adler, Earle, U.S. pat. 2,933,395 (1960 to General Foods).

Crystal structure: Sutor, Acta Cryst. 11, 453, (1958). Synthesis: Fischer, Ach, Ber. 28, 2473, 3135 (1895); Gepner, Kreps, J. Gen. Chem. USSR 16, 179 (1946); Bredereck et al., Ber. 83, 201 (1950); Crippa, Crippa, Farmaco Ed. Sci. 10, 616 (1955); Swidinsky, Baizer, U.S. pats. 2,785,162 and 2,785,163 (1957 to Quinine Chem. Works); Bredereck, Gotsmann, Ber. 95, 1902 (1962).

Hexagonal prisms by sublimation, mp 238 C. Sublimes 178 C. Fast sublimation is obtained at 160-165 C under 1mm press. at 5 mm distance. d 1.23. Kb at 19 C: 0.7 x 10^(-14). Ka at 25 C: <1.0 x 10^(-14). pH of 1% soln 6.9. Aq solns of caffeine salts dissociate quickly. Absorption spectrum: Hartley, J. Chem. Soc. 87, 1802 (1905). One gram dissolves in 46 ml water, 5.5 ml water at 80 C, 1.5 ml boiling water, 66 ml alcohol, 22 ml alcohol at 60 C, 50 ml acetone, 5.5 ml chloroform, 530 ml ether, 100 ml benzene, 22 ml boiling benzene. Freely sol in pyrrole; in tetrahydrofuran contg about 4% water; also sol in ethyl acetate; slightly in petr ether. Soly in water is increased by alkali benzoates, cinnamates, citrates, or salicylates.

Monohydrate, felted needles, contg 8.5% H2O. Efflorescent in air; complete dehydration takes place at 80 C. LD50 orally in rats: 200 mg/kg.

Acetate, C8H10N4O2.(CH3COOH)2, granules or powder; acetic acid odor; acid reaction. Loses acetic acid on exposure to air. Soluble in water or alcohol with hydrolysis into caffeine and acetic acid. Keep well stoppered.

Hydrochloride dihydrate, C8H10N4O2.HCl.2H2O, crystals, dec 80-100 C with loss of water and HCl. Sol in water and in alcohol with dec.

Therap Cat: Central stimulant.

Therap Cat (Vet): Has been used as a cardiac and respiratory stimulant and as a diuretic.