The structures of the pyrimidines and purines. VII. The crystal structure of caffeine

Abstract

Caffeine crystallizes in the monoclinic space group P21/a with a = 14.8, b = 16.7, c = 3-97 A, fl = 97"0 °. The crystal structure was solved by an application of the isomorphous-replacement method and a consideration of the possible hydrogen bond system in the crystal. A comparison is made of the intramolecular distances with those in other purines and a pyrimidine, and indicates that steric hindrance must be allowed for in a theoretical calculation of bond lengths in relatively complicated molecules of this type. Evidence for and against the existence of a short hydrogen bond between water molecules is given.A C 11 32

Structural chemistry of N(7)-substituted purines: the crystal and molecular structure of 7-methylxanthine hydrochloride monohydrate

“…Complete heavyatom bond lengths and angles are given in Table 2. The C-H bond lengths average to 0.97 (4) caffeine (Sutor, 1958;Shefter, 1968) and theobromine (Shefter, Brennan & Sackman, 1971)]. As expected however (Kistenmacher & Shigematsu, 1974, 1975, there are significant adjustments in the interior bond angles in the imidazole ring due to the protonation at N(9).…”

X-ray and Neutron Diffraction in the Study of Organic Crystalline Hydrates

“…Since this process is accompanied by pseudomorphosis, i.e., the destruction of the mother crystal into a multi-crystalline powder of the same shape, indicated by the clear single crystal turning opaque, the loss of water is connected with a major change in structure as is characteristic for stoichiometric hydrates. Caffeine 0.8 hydrate [35][36][37] and theophylline monohydrate [38,39] form channels in their structure as well. Both materials are isostructural and stoichiometric, while the water release behaviour from the channels differs significantly [40][41][42].…”

Molecular structure of caffeine as determined by gas electron diffraction aided by theoretical calculations

“…Although it is a common understanding that the above-mentioned effect of caffeine is brought about by its structural resemblance with adenosine and cyclic-AMP, no reliable experimental molecular structure even in the crystal has been reported. The crystal structures of caffeine hydrate have been reported [7,8], but the structural determination of pure anhydrous caffeine has not been successful because of the difficulty in preparing the fully ordered crystal [5,6].…”