Δ-Tetrahydrocannabinolic acid A, the precursor to Δ-tetrahydrocannabinol (THC).

While Δ-tetrahydrocannabinolic acid A (THCA-A) has been reported to be difficult to crystallize and/or amorphous, we have obtained THCA-A in a pure crystalline form by extraction of marijuana and selective fractionation with liquid CO. THCA-A (systematic name: 1-hydroxy-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c]isochromene-2-carboxylic acid, CHO) crystallizes in the orthorhombic space group P222, with Z = 8 and Z' = 2. The two independent molecules are related by a pseudo-twofold axis centered between the two -COH groups, but the conformations of the two -CH chains are quite different (tgt and ttg; t is trans and g is gauche).