The crystal and molecular structure of delta-9-tetrahydrocannabinolic acid b.

The crystal and molecular structure of the title compound C-22H-30O-4, has been determined by X-ray methods using 1106 reflections above background level collected by counter methods. The crystals are orthorhombic, space group P2-12-12-1 with cell dimensions a equals 16.514(2) A; b equals 14.324(2) A; c equals 8.744(1) A; there are four molecules per unit cell. The structure was refined to an R of 0.084 (weighted R-w equals 0.068). The cyclohexene and the pyran part of the molecule occurs in the half-chair conformation. The bond distances and angles, and a slight twist of the benzene ring, indicate considerable stains in the aromatic system. Both the phenolic and carboxylic group are significantly out of the plane through the aromatig ring. The angle between this plane and a plane through the cyclohexene ring is 37.7 degrees. The pentyl sidechain occurs in an extended gauche conformation, and the thermal parameters of this part of the molecule are very high. The molecules are held together by van der Waals forces in the c-directions, and hydrogen bonds (2.688 A) from phenolic to carboxylic groups in the a-b plane. There is a short ultra-molecular hydrogen bond (2.490 A) from the carboxylic group to the pyran oxygen.