ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 22, Number 2
JKCSEZ 22(2)
April 20, 1978 

The crystal and molecular structure of theophylline hydrochloride has been determined from X-ray data by Patterson techniques. The structure has been refined by block-diagonal least-squares and Fourier synthesis on three dimensional data. The unit cell is orthorhombic, space group Pna21, with a = 14.01, b = 11.49, c = 6.77Å, and contains four molecules. The final R value based on 743 observed reflexions is 12.2%. The intramolecular distances are similar to those in other compounds containing a purine or pyrimidine group. The molecules are nearly planar and are stacked in layers parallel to the (001)plane. The chlorine atom is coordinated to N(1) atom at a distance of 3.06Å. The structure is stabilized mainly by van der Waals interactions; however, a short N…Cl contact of length 3.06Å, which is slightly less than the expected van der Waals separation, suggest that weak charge transfer interaction may be present. The relationship between this structure and the known structures of theophylline monohydrate and caffeine monohydrate are discussed.